Environment: We shouldn’t be cast as the bad guys.
Date Published:
Synopsis: Nature only provides a small window for life’s only hope, human science & technology.
Much discussion of the environment focuses on anthropic climate change with subtext that we humans are the bad guys destroying our wonderful planet, but this is about looking at our role in perspective, which may even help reconcile both sides of the debate, although that is a challenge! Science, and the Monty Python universe has put our place in the universe in perspective, and the goal here is to put our time and our current environment in perspective within the timeline of the Earth.
The focus is on natural climate change and leaves the more divisive topic of anthropogenic climate change and human impact on the Environment to other discussions. While our technology may possibly bring about our own end, without technology, nature will definitely limit our existence to less than 1% of the Earth’s history, just as it has with every other species of complex life. Either way, unless we managed to use our technology to extend our time on Earth instead of cutting short our own time, the negatives from our technology will have very little impact on the “bigger picture” of the cycle of life on Earth. We may cut short the survival of our own societies, but it is nature that will end life on Earth.
Nature is amazing and wonderful, but it is also destructive. Realising that we humans are not living on an all-caring planet almost perfect planet, but rather, on a planet normally uninhabitable for us humans, gives another perspective.
Perhaps more surprisingly, as explained in detail in the section “the big picture” below, the record of the past shows Earth’s environment has mostly been hostile to “visible life”, which is why we call the most recent 10% of the Earth’s history the Phanerozoic Eon, with Phanerozoic meaning “visible life”.
As covered in detail in the section “Even during the Phanerozoic, climate always changes” below, even with the “visible life Eon” most of the time the climate is not suitable for humans. Our species has survived 300,000 years only because during that the climate has remained close to the climate experienced when we first evolved, and we have thrived this last 10,000 years because the climate of the place and time we first evolved has become present across the globe and this length of stable temperatures at current levels is to our knowledge unique in Earth’s history. While Earth is for a brief window of time providing an almost perfect environment for us humans, nature will inevitably close that window ensuring we, like all species of complex life before us, exist for less than 1% of the Earth’s history.
Ok, so what about the future?
To grasp that reality of how harsh nature really, I had break from my long-held assumption that Earth’s environment and climate must normally be like it is now, has been quite like this from when life began billions of years ago, and will remain this way until the time the Sun explodes in around 5 billion years.
But gradually as I looked deeper, what I found was that those long held assumptions were based misinterpreting data, and it turns out the world we see now is as misrepresentative of Earth as a burst of visible life in the desert after rainstorm is of the natural state of a desert. For Earth, the current already declining burst of visible life is representative of how the Earth is around 10% of the time.
Having heard that in around 5 billion years the Sun will explode to a size so large it almost swallows the Earth, I had assumed that event would be the end for life like us humans. For me, the plot thickened when I learnt, as can now be found from an internet search, that life on Earth will far earlier, in around end long around 1.5 billion years. Spoiler alert, the author who concluded that if it takes 1 billion years until the oceans boil, that does not mean humans have 1 billion years left. While we may be able to than more than +2oC increase, we sure can’t handle the around +80oC needed to boil all the oceans! Using this and looking back raises the question “if the Sun is always getting hotter, does that mean Earth has always been getting hotter, and was therefore colder in the past?”
The green line shows global average temperatures past and future using data from thepaper by Franck et al.
In fact, instead of the Earth having been continually getting hotter as the Sun turns up the heat, Earth began with surface temperatures like those still underground in volcanoes, and instead of getting hotter, so far, the surface has overall been getting colder. We can only be confident they Earth has been cool enough for visible life during the most recent 10% of its timeline.
life has the surface consistently provided a climate cool enough to be suitable for “visible life”, and while we are now in the Phanerozoic Eon, from the Greek for “visible life”, temperatures are about to start rising again.
Combine the past that was too hot with a future where the oceans will boil away, and the picture is a planet that has only a relatively short dip in the middle to temperatures suitable for visible life.
From Ted Talk by Johan Rockström: “We’ve had a 10,000 year where our civilization had developed where we have had an enormous privilege of a planet at 14°C +-0.5°C”.
The section below “Even during the Phanerozoic, climate always changes” below covers the details, but the takeaway is that the time of conditions on Earth that can support the human civilization around the globe, as Earth does now, began only just over 10,000 years ago. These conditions have definitely never previously occurred in the time since humans evolved, and almost certainly not ever before in the entire history of the Earth. After looking at data on the past that can be verified from multiple sources, it becomes clear we can’t count on current conditions that support our society naturally, continuing for even another thousand years. The reality is that if you arrived at Earth in a spaceship at a random time, there is a less than 5% chance anywhere on Earth would be naturally habitable for humans, and an around 0.0002% of encountering a planet able to support billions of humans around the globe.
Many of us get our first ideas on creation from traditional creation stories where Earth was basically like it is now almost from the outset and could supported humans as it does not almost the entire time. There is more up to date science, and most education systems provide mostly history within the time of civilization, which is just 10,000 years of a 4.5-billion-year history, but the thought that the Earth is normally like it is now can still linger despite knowing better. Even the information science provides on the bigger picture can be very misleading, with words such as “life” and “Ice Age” having very different meanings in geological history than the same words are taken to mean in day-to-day usage, and concepts such as the Earth being in the “Goldilocks zone” being quite misleading.
If, like me, you first assumed that the current quite agreeable climate as observed not just for the last few centuries but throughout recorded history, must be “normal” for Earth, then the idea that what we are experiencing now this is a brief and atypical window of conditions where Earth supports the life we see around us, and that this planet is normally hostile to any life beyond single celled organisms, is going to require both time and supporting information.
However, as covered in detail “the big picture” below, yes, the current Earth environment is in some ways like a desert in bloom with flowers and other life after a rainstorm, with the supporting information on the how and why explained covered below, the current Phanerozoic of Eon of visible life is exits in a cool period on planet where temperatures that have fallen to reach the current low are about to start rising until they are too hot for life.
But even during this Phanerozoic Eon where the Earth provides an environment that allow for visible life, constant climate changes lead to continued extinctions, with the current atypical climate that supports our civilization something that would soon end naturally even if human activities don’t hurry things along.
The paradise for us that Earth is now is the result of a period of exceptional stability, but natural environmental change is like a sleeping “grizzly bear” that periodically wakes and disturbs the environment, causing extinctions, and forcing evolution to adapt for any life to survive. While now is “paradise” for humans, within the blink of an eye on nature’s timescale, “the bear” will wake and the time Earth naturally support humans in such record number will end.
Whilst the less than +2°C since the start of the industrial age increase is worrying for us humans, it is very modest relative to past climate changes. Even within the Phanerozoic Eon of “visible life” has seen global temperatures of +20°C higher and -8°C colder than the current +14°C.
Much of the current wave of species extinctions are due to habit loss and other aspects of human impact, as human technology and the atypically stable climate of the past 10,000 years has enabled “accessorised evolution” to advance civilization and human population growth to a level that, within a biosphere that itself is not growing, means displacing other species. But this civilization depends on the current atypically stable climate, and few species as vulnerable to the impact of climate change as human societies with cities and farms and infrastructure making it far more difficult than ever for humans to relocate.
Humans alone are unlikely to induce climate change much beyond around +2°C because the impact on climate would from that point disrupts the human civilization driving the change. It takes not that long at anything beyond +2°C for the changing climate to disrupting farming and sea levels would soon after cause a dramatic reduction in the human population, which in turn would limit the further impact of humans on the climate. The fact that human civilization is so sensitive to climate change makes any risk from humans alone, mostly a risk only to humans. For most of rest of nature, while humans are the current risk, over time, the real risk is natural climate change.
However, once the climate starts changing, and even if we don’t “poke the bear” it will relatively soon, all data confirms that effects like the albedo effect usually take hold to amplify the changes. The danger of “the grizzly bear” of natural climate change waking is the real threat, even without humans.
Nature is the real bad guy big grizzly bear of climate change, and while it has been in hibernation for around 10,000 years, either we are witnessing the real bad guy of natural climate change as a grizzly waking by itself, or humans poking that bear. Either way, while humans could start process, the threat from nature is far greater than from humans. Natural climate change normally means either dropping into full glaciation Ice Age with sea levels 170m lower, but huge parts of the Earth covered in glaciers, or temperatures between +4°C and +20°C higher which even at the lowest levels restrict where humans can live produce sea levels 70 meters higher. While some significant consequences of natural climate change could take decades, unless it could be reversed at the very least devastate our society and dramatically reduce the population we can sustain.
Every species with the complexity of a vertebrate so far has only ever enjoyed a very short span of existence before becoming extinct. On the other hand, humans being the first species with accessorised evolution are the first with the potential to control the climate and extend their existence, that is provided the technology is not used instead to destroy accelerate our own demise.
Sooner or later humans will either take the role of the good guys and commit to being gaining the ability to impact the climate and even become a multi-planet species or admit defeat and just accept that all this will end.
The big picture: We in a rare cool moment for Earth’s surface.
Earth’s environment is usually hostile to “visible life”.
You may be as surprised as I was to discover that no, the Earth’s current environment that results in a planet teaming with life is less representative of what is “normal” than a brief bloom of life after rain in a desert is representative of a desert.
The 4.5 billion years of Earth have only supported “visible life” for 0.5 billion of those years, and the future will only provide for a similar ratio of support for “visible life”.
Not only is the core or the Earth still hotter than the surface of the Sun and volcanos remind us that intense heat is also never that far from the surface, but only in this small window in the middle of the life of the Earth circling a main sequence star are temperatures on the surface cold enough for us.
For the entire 10-billion-year period from the formation of the Earth until of the “death” of the Sun:
47%, or just under half of the time the Earth supports any form of life
Mostly the Earth is home only for microorganisms invisible to the human eye.
12% of the time the Earth supports some form of “visible life”.
<3% of the time the Earth provides naturally conditions that could support human life.
Here is a brief summary of Earth’s past and future environment:
4.6 billion years ago the Earth formed and entered 0.8 billion years of the Haedon “hell on Earth” Eon of massive bombardments and intense heat.
3.8 billion years ago, the first life had formed to launch the 1.3 billion years of Archean “beginning of life” Eon as single celled life began on a still around 60°C hot planet with atmosphere of almost entirely carbon dioxide but under less heavy bombardment from space.
3.2 billion years the S2 meteorite 50 to 200 times larger than the one that triggered the end of the age of dinosaurs slammed into Earth, but unlike the mass extinction of complex life of 60 million years ago, the hardy microbes of the time were boosted by the impact, and the disturbance helped the single celled life properly take hold on Earth.
2.5 billion years ago, oxygen began to appear in the atmosphere at the beginning of the 2.3 billion years of the Proterozoic “earlier life” Eon that transforming the Earth into a planet capable of hosting complex life.
2.4 billion ago the emergence of free oxygen in the atmosphere caused the “Oxygen Catastrophe”, which forced the single celled life, that was then the only life on Earth, to evolve to survive in an atmosphere with oxygen or perish.
Between 0.75 billion and 0.55 billion years ago, as the Earth continued cooling towards temperatures that could allow for complex life and even humans to survive, it is believed during “icehouse climate events” the Earth even experienced “Snowball Earth” events with almost the entire surface covered in ice.
0.55 billion years ago the Phanerozoic Eon of “visible” life began, with what we normally think of as life finally taking hold as the Cambrian explosion. The early Phanerozoic was a time of more life on Earth than ever before or ever since.
550 million years ago despite a cooler Sun than that of today, average global temperatures were at over 35°C, which is over 20°C higher than the 14°C of today, due to CO2 levels several times higher than those of today. The higher temperatures and higher CO2 levels supported a biosphere double that of today, but unfortunately would not support humans.
Around 450 million years ago temperatures plummeted causing a mass extinction in the first “ice-age” of the Phanerozoic, the
Then another hot period with av temps over +25°C until either one long ice or a series of ice ages, with temperatures swinging between +18°C and -8°C.
Then 250 million years ago temperatures again rose above +30°C and kick off the age of the dinosaurs which continued until without an ice-age for over 180 million years until the meteor impact 65 million years ago.
temperatures continued to fall for around 30 million years after the meteor until the beginning after the meteor until around 33 and the current Late Cenozoic Ice Age (Wikipedia).
Anytime between now and around 25 million years from now, the Late Cenozoic Ice Age will end, threatening the survival of humans.
Between 50 and 150 million years from now it would be logical to declare the end of the Phanerozoic Eon, but unless technology can override nature to an amazing extent, neither humans nor any other mammals would be present to name the new Eon.
The last complex life, probably something like tardigrades, would become extinct within around 600 million years.
The very last microbes would be extinct within just over 1 billion years.
Around 5 billion years from now, the Sun would come to the end of its “main sequence” and “explode”.
This picture is at odds with the idea of a perpetually nurturing planet given by repeated messaging of “we are on this very rare and special planet with an environment and climate that supports us, and we need to appreciate look after our planet”. Perhaps that message should be replaced with a message of “we are in this very brief and special time where the environment and climate at supports on our planet, and we need to appreciate the moment and take advantage of it while it lasts”.
Religions have normally been mostly interpreted as suggesting we are in the centre of the universe, and that Earth’s environment was from the outset on Earth was suitable for us humans. Of course it was all about humans, as even most gods credited with playing a role in creation are depicted as looking very much like humans.
It can be hard to grasp how far from “normal” conditions are on Earth today. Conditions on Earth now are even very different than it was for the dinosaurs, and vastly different from those during most of the time life has existed on Earth.
We think of conditions like those of today being necessary for life, and it follows from that that if there has been life on Earth for billions of years, then the environment of today must also have been around for billions of years.
Concepts like being in the “Goldilocks zone” sounds like being in the zone where temperatures are suitable for us humans, but the misleading part is that being in the Goldilocks zone and supporting life doesn’t actually require conditions at all suitable for an actual human Goldilocks, doubt about one so fussy as to find papa-bear’s porridge is too hot. For billions of years the only life on Earth was just microbes, Earth has only supported the visible organisms we usually think of what we see think of as “life” for a relatively brief time.
ProcaryotesEucaryotesFor billions of years the only life was just microscopic single cells.
The misleading part comes from the idea that supporting “life” means having conditions that allow us humans, our pets and farm animals to survive, when instead it means having conditions that allow the survival of single celled life that almost 30 minutes at over 120°C (250°F) in a sterilizer to eliminate.
At one time I thought early life was like trilobites or something, but it turns out even trilobites are considered modern complex life.
The graphs here show how that even today, more than half the total biomass of all living things is single celled organisms that are each too small to see with the naked eye. Even our own bodies contain 10x more non-human bacteria cells than human cells, although these simple cells are smaller so by mass, so we are still mostly human cells by mass.
While the Earth has supported single celled life since almost the beginning, it is only in the Phanerozoic Eon which is the most recent 10% of Earths life, that Earth has been home to complex multicellular organisms like us, or any of the plants and animals we can actually see as individual living things.
This is not just because complex life had not yet evolved, but also because there was too little oxygen, no ozone layer to stop the radiation killing life on the surface, and for creatures like us, almost the entire time up to the Phanerozoic eon, as can be seen from green line on the diagram, Earth has been just too hot.
The “faint young Sun paradox” (see – Wikipedia) is that when life on Earth began 4 billion years ago, Earth was far warmer than it has ever been since, despite the early Sun only generating around 70% of the energy it does today. Two factors explain how it is that average temperatures on Earth have so far been continually falling despite energy from continually increasing as the Sun, like all main sequence stars, continually heats up through its lifetime as it heads towards an eventual explosion:
As can be seen from the graph from the Wikipedia faint young Sun page, CO2 levels have fallen dramatically over time. Note the scale for the CO2 levels is logarithmic, so the time to reduce from 100x current levels to 10x current CO2 levels is similar to the time from 10x current levels until the now 1x level. That, the fall in CO2 level is proportionate the CO2 level itself, and in absolute terms the fall is slowing.
The big picture is that for the whole 4.5 billion years since the Earth formed, while temperatures have bounced around a lot, the overall trend has been that despite orbiting an ever-warning Sun, temperatures on Earth’s surface have been progressively falling, although, as the green line on the diagram above shows, they are about to start rising again.
We are at what is basically the lowest point on the graph of long the long-term trend of temperatures on Earth. This diagram recaps on this big picture of the entire life of the Earth from the perspective of life, with the coldest points marked in blue, and note that we have been in the Quaternary glaciation for over 2.5 million years:
While Earth has so far been progressively getting cooler, through reducing CO2 levels and the greenhouse effect at a rate fast enough to override that heat from the Sun has been increasing, as CO2 levels fall, so does the impact of further CO2 level reductions. We have now reached the point where CO2 levels fall at on average about the rate needed for stable temperatures, which has enabled this Phanerozoic eon “fully Goldilocks window” to provide a period of relatively stable temperatures and finally enabled the evolution of complex life.
While that in the past, Earth was most of the time not the nurturing home for complex life that the narrative suggests, after 4 billion years of cooling and with temperatures over the longer term having “bottomed out”, we are currently experiencing in this Phanerozoic “fully Goldilocks window” a planet that is for now, finally supportive of what most people consider “life”. But it is not because it took so long for the Earth to provide this environment that I declare nature to “be the real bad guy”, but because this current atypical environment won’t last, and the Earth is soon to start naturally returning to the higher temperature of the past.
“The flip” from cooling to warming that will progressively end all life on Earth.
So why will the Earth flip from cooling to warming in order to become this “true bad guy”?
The why is because with CO2 levels now down to being measured in parts per million, the scope for further reductions is running out as there is little CO2 left to reduce. While dropping CO2 by 4 parts per million can keep Earth’s temperature stable and offset Solar increases, another 25 million years of such reductions would result in record low levels of CO2 and the lowest levels that at which photosynthesis could continue. What this means is that within 25 million years, we reach the end of the long-term trend of global cooling, and switch to global warming, because reducing, because 25 million years is the longest possible time that plants can tolerate continual reductions in “excess” CO2 to counter the warming sun. Within 25 million years, Earth switches, from the cooling trend of over 4.5 billion years, to a warming trend of another 5 billion years until the Sun explodes, that will end all life within 1.5 billion years.
Any informative internet search on “how long will life on Earth survive” reveals that, as can be seen from the green temperature line in the diagram above, all life on Earth will end in around 1.5 billion years.
I think most people have heard how the Sun will explode in around 5 billion years, which is so far off that it feels entirely academic, and little different from forever. The “why” life will on Earth will end in 1.5 billion years is because, instead of “all is fine and then the Sun explodes in 5 billion years”, as the Sun is getting progressively hotter and the Earth’s compensation mechanism will have ended, in 1.5 billion years the Earth will be too hot for all life.
Again, it is not like “all is fine and then in 1.5 billion years life ends”, but instead it gets progressively hotter, and while the first procaryote life that began when the Earth was hottest can last 1.5 billion years, it is only the single celled “just slime”, that can last over 700 million years. Stilla long time. Of course, again it is not all perfect and one day 700 million years from now suddenly all the visible life from the “fully Goldilocks” Phanerozoic, multi-celled life dies at once.
Now is the coldest of the coldest, at the bottom right.
The timeline of extinctions from the flip to the Earth heating instead of cooling is discussed in more detail below, but just as different forms life arrived ass the Earth cooled, they will become extinct as the Earth warms. This means the first forms of life to exist will be the last to become extinct, and the most recent arrivals are the first to become extinct.
As we humans evolved during the 2.5 million years of the very coldest Glacial period, the Pleistocene glaciation (which is technically an ice age), of the already overall coldest time Eon in Earth’s history, the Phanerozoic, we are one of the species least equipped to deal with increasing temperatures, and as such would naturally be one of the first to become extinct if our technology cannot save us.
Earth in the current state is like a desert bursting with flowers and life after unique rain event. Instead of gloating about how we live on a wonderful planet, we should probably just be thankful we live at a unique and wonderful time on what is normally a hostile planet.
But this “bloom in the desert” won’t last, and while the prospect of humans being the “bad guys” and tarnishing the bloom a small fraction before nature ends it once and for all will make no significant difference on geological timescales and would not even end the “bloom” of visible life of the Phanerozoic, doubt all those single celled organisms. No, nature will play the role of the true bad guy unless we can intervene.
Even during the Phanerozoic “bloom”, climate always changes.
As already discussed, there is the long-term climate change from way too hot, to “just right” and back to way too hot, but on that big picture the temperature shown by the green line, at least during this relatively small “just right” Phanerozoic time of “visible life”, looks like it doesn’t change very much.
Although the around 10% of the Earth’s full life that is the “fully Goldilocks” Phanerozoic time of “visible life” does provide the only period when Earth supports what most of us think as “life“, it is still a time of change of climate so severe it causes waves of mass extinctions.
Most times you hear “the climate always changes” it is intended to dismiss the idea that climate change presents any significant threat and is made by people who have not really “done their own research” and tend to assume climate change means events such as the “Medieval warm period” and the “Little ice age”, and not realise our civilization has emerged during an unprecedented period of near perfectly stable climate.
25 million more years of Phanerozoic means not paradise, but real climate change.
While there is still 25 million years’ worth of time where CO2 reductions can keep temperatures from rising before “the flip” become inevitable, this oasis of visible life Phanerozoic eon has not always been the paradise for us we see today, and nor can we count on current conditions continuing for even another 1,000 years, because even within this Phanerozoic time of the “bloom of visible life” on our the normally lifeless looking planet, the climate always changes.
Graph 1, of the diagram here shows the long-term outlook from the Frank et al paper. At this resolution climate look stables, but that is mostly because this is the entire lifetime of the Earth graph and as such only shows long term trends.
The blue funnel shows mapping from graph 1 to graph 2, with graph 2 showing the more detail of temperatures of the past 500 million years, as compiled by Scott Wing of the Smithsonian. This illustrates how temperatures in the Phanerozoic have swung back and forth between over 20oC hotter than the current global average temperature to 4oC cooler.
Most recent 2000 years
Graph 3 from showing temperatures calculated from Vostok ice cores provides an explosion as shown by the yellow funnel of the most recent 420,000 years from the “now” section from graph 2, the graph by Scott Wing of the entire Phanerozoic temperatures, revealing that temperatures over the entire time of humans have always been far cooler than typical temperatures, with the purple funnel to graph 4 of the past 24,000 years showing the path to the current period of stable temperatures.
Temperatures during this Phanerozoic window for visible life are the coolest the Earth will ever experience, but as can be seen from graph 1, fluctuate between widely between 20°C warmer and over 4°C colder than then current global average of around 15°C, with the continual changes causing continual extinctions and rapid changes that create major extinction events.
Humans evolved and have only ever existed in colder than normal temperatures that technically qualify as an Ice Age.
The most recent 10,000 years during which humans developed civilization have provided the only time in the past 500,000 years with this level of temperature stability temperature stability, and almost certainly the only such period ever at close to a global average temperature of +14oC.
The bottom line is what we are now experiencing is an unprecedented period of temperature stability at a temperature that allows humans to live on most of the planet, and plant crops and build cities without the constant need to relocate as climate changes.
All this during an unusual state within an ice age, on a planet where not only are ice ages not the normal state, but the entire window for visible life is itself atypical.
Even in the Phanerozoic, constant changing climate produces constant extinctions.
It is well reported that in addition to events like the Oxygen Catastrophe and Snowball Earth events that took place even before the Phanerozoic, there have been 5 mass extinction events during the Phanerozoic, and each of these is about climate change triggered by volcanoes or even meteors, poking the bear and triggering nature into extended runaway climate change. The most severe Permian-Triassic extensions of 250 million years ago saw a rapid jump from temperatures of the typical coldest to the typical warmest levels of the Phanerozoic.
After the Permian-Triassic “great dying”, dinosaurs dominated the Earth for over 180 million years, even surviving the next mass extinction of the Triassic-Jurassic. Note that the 180 million years of the dinosaurs was the longest period of in the Phanerozoic time of visible life without an actual ice-age. Ice ages are indicated as the blue highlighted areas of the timeline on the graph of Phanerozoic temperatures by Scott Wing.
Also note that where were over 1,000 species of dinosaurs, so 180 million years of dinosaurs surviving was a succession of different species, and no one species lasted anywhere near 180 million years, as although those 180 million years represent the longest time span of the Phanerozoic Eon without an ice age, climate there was still always climate change sufficient to cause extinctions.
While the greatest mass extinctions normally follow the switch between full ice-age and maximum temperatures, the Triassic-Jurassic mass extinction followed a fall from near highest temperatures to the brink of an ice-age, and as there is always changes to climate, there is also always a proportionate rate of extinctions.
Individual species did not survive anywhere they were different species did not that could survive kept changing with, for example, Triceratops surviving 3 million years (68-66Ma), Stegosaurs 10 million years (155-145Ma), and various Tyrannosaurus including T-Rex combined survived almost 6 Ma (72.7-66 Ma). Even with species we think of as having been around since the age of the Dinosaurs like Crocodiles, while the crocodile class of animals has been around for hundreds of millions of years and current species look their ancestors to us, individual crocodile species alive today have typically existed less than 10 million years.
Ice ages: not necessarily what you think, and we are in one.
The graph in the sections on extinctions above shows the three ice ages of the Phanerozoic, but the term ice-age in geology differs from now common popular use, leading to some ambiguity between the terms “glacial period” and “ice-age”.
There are actually two meanings of the term ice age:
The technical Earth scientist “ice age” meaning anytime the Earth is partially covered by glaciers, including now and all of the past 33 million years of the Late Cenozoic Ice Age (Wikipedia).
The general non-scientific wider use of fully “ice age” referring to the last glacial period or any of the past glacial periods when the Earth was even more covered with ice than now, as in the film “Ice Age“.
Now is the coldest of the coldest, at the bottom right.
All agree that an ice-age is a significant time period when there is far more ice on Earth than “normal”.
For most people now is normal, so an ice-age is time with much more ice than now, but for scientists studying the history of the Earth, normally the Earth has no significant ice at all, so any time when there is significant ice, including now, is an “ice-age”.
This means for scientifically, it is now still an ice age, the Late Cenozoic Ice Age (Wikipedia), but the adoption of the term “ice-age” to mean “colder than now” has led to “glacial period” being sometimes used instead of “ice-age”.
We are currently in the middle of a glacial period (although it’s less intense now than it was 20,000 years ago) but this is not the only period of glaciation in Earth’s history; there have been many in the distant past, as illustrated in Figure 16.2. In general, however, Earth has been warm enough to be ice-free for much more of the time than it has been cold enough to be glaciated.
This means, overall, from the perspective of climate, we humans are thriving in so far unique period of stability during the least common climate phase of an interglacial period of glaciation, and just being in a glaciation is already a rare state for Earth. How long can this stability of the least common phase of a rare event last?
As can be seen from the graphs of different timescales with ice ages marked with blue highlighter, most of the time the Earth is not in any level of ice-age.
The entirety of these light blue blocks are areas described by geologists as “ice ages”, although as can be seen from glacial-interglacial diagram, they consist of both “glacial” (marked in dark blue) and “interglacial” periods marked in yellow. In popular culture, we only refer only to the dark blue “glacial” periods as an “ice age”, because since we are now in an interglacial, the “yellow” areas are like now and to us seem normal. We are currently in a warmer interglacial phase of the current Quaternary glaciation.
While the dark-blue glacial phases have colder temperatures, than the usually relatively brief yellow highlighted “interglacial periods” as we are in now, that is not the only difference. During glacial periods as well as large areas of the globe being either covered with ice or too cold for us humans, sea-levels during glacial periods can be 130 metres lower than now. , and much of the planet would be too cold us, returning to a glacial period sounds less appealing than returning to a “greenhouse” period without ice, but for humans, the “greenhouse” would be worse with temperatures +8oC above current levels and sea levels 70 metres higher.
In addition to the 3 ice ages of the Phanerozoic, there were at least two ice ages that could have even been “snowball Earth” events prior to the Phanerozoic, but overall, the Earth is usually too warm for ice.
The normal pattern for the Earth, even during the is to be warmer than now, and without any significant glaciers on the surface. The black area to the right covers the entire time for complex life on Earth, with the blue areas covering the glacial periods.
The above “full Earth history” scale shows a much higher percentage of the Pherozoic as being an ice-age, and the overall trend of the wiggly line of the graph by Scott Wing of the Smithsonian shows the trend has been for a fall in temperature during the Phanerozoic, this is all due to the CO2 levels having fallen faster than required for stable temperature, but with “the flip” fast approaching, ice-ages will are about to end forever.
The chart to the by Scott wing shows the full pattern of climate during the Phanerozoic, with the three significant dips into the blue area, corresponding to the Andean-Saharan, Karoo, and the current Cenozoic glacial periods. Apart from those glacial periods and the small dip into blue around 180 million years ago, the rest of the graph is red with temperatures at least 4oC above current levels and no polar ice caps.
Humans are warm blooded creatures of an Ice Age.
This current late Cenozoic ice-age includes the entire time period when humans have existed, and even the period when human ancestors evolved prior to homo sapiens.
The entire Cenozoic era or “age of mammals”, not just the current ice age, has been a time of ice-age or near ice-age conditions far colder than the average temperature of the Phanerozoic and always colder than the coldest temperatures experienced during the reign of the dinosaurs.
New Evidence We Are Entering An Ice Age Termination Event – EXPLAINED
As on mid 2024, global temperatures have reached +1.5°C above the average of the previous 10,000 years, and every time in the past temperatures have reached +2.0°C from that average, either the ice age has ended, or the Earth has gone into full glacial “what everyone calls an ice age” with large sections of areas of the Earth where there are currently billions of people becoming covered with ice.
In fact, the entire time humans and the immediate ancestors have existed has been during a glacial period, on what is normally an ice-free planet, so while we know for certain that humans can survive during the cold climate that differs from the normal climate during this “fully Goldilocks window” called the Phanerozoic when conditions are best for complex life like us.
Plus, we have only thrived and had civilization and billions of humans during the only 12,000 years ever in the Earths 4-billion-year history with a stretch of 12,000 years at this temperature.
While ending the current ice age may sound preferable to things getting colder, every time in the past an ice age has ended, the loss of polar ice caps not only raises sea levels by 70 metres, but it also reduces the effect of the ice reflecting heat from the Sun which sees global average temperatures continue to rise to at least +8.0°C above that average human civilization has experience, and +6.0°C from what humans have ever survived in the past. The over 1,000 who died from heat during the Hajj in 2024 may provide a small preview of what happens to warm blooded mammals that evolved during an ice age once temperatures increase.
At the very least, no matter which direction temperatures move, it would only take what is historically a remarkably small shift in temperature to restrict where on the planet humans can live and/or farm, forcing a dramatic fall in the human population and devastating societies around the globe.
For us humans it has been all ice age, but it has still also been all climate change.
Humans having been around for 300,000 years, and, prior to the most recent 12,000 years, have had the very real experience of the climate always changing. The fact that common usage of the term “ice age” is to refer to a time just over 15,000 years ago serves as a reminder how much colder Earth has been during the time humans have been on Earth.
Perhaps around 150,000 years ago, ice records indicate near this current level of climate stability, but at temperatures around 8°C (14.6°F) cooler than today. but generally, at times in human history prior to the past 12,000 years, temperatures were almost always either rising or falling and the climate was continually changing.
Graph of reconstructed temperature (blue), CO2 (green), and dust (red) from the Vostok Station ice core for the past 420,000 years: Wikipedia
At no previous time has the temperature remained at the “+0” point for anywhere near the current 12,000-year stretch.
Further, the reconstructed temperature and CO2 data shows that maximum temperature during the past 450,000 years of the Quaternary glaciation is at most 2 degrees above current levels, which last occurred around 130,000 years ago.
Given humans have existed for over 300,000 years, it is clear that humans can at least tolerate a changing climate and a brief period of temperatures +3.0oC above current levels, and as much as -8.0oC below current levels.
Humans and our civilization: How long have we got?
We are on a 4.5 billon year old planet, where until the past 0.5 billion years, a human would need to wear a spacesuit to survive because there was no oxygen, too much radiation and it was too hot. But that is the past, and we live in the present with an ozone layer, an ideal level of oxygen for us to beath, and temperatures that enable us live almost anywhere on the planet. The question for the future, is how much longer conditions will be so suitable for us humans given the planet is about to switch from the cooling phase to warming phase.
The end of the current ice age, if we cannot prevent it, would end almost all of our current civilization, and if as suggested by Dr Ben Miles, that end has already begun, civilization could end within a century.
Even during these “good times”, as I have said, climate change means no species of complex life has ever existed for 1% of Earth’s history, and as 1% would equate to 45 million years, it is a reality that we know of nothing that has come close.
“I don’t think there is evidence that any single species has been around for more than a few million years,” Africa Gómez, an evolutionary biologist at the University of Hull and senior author of the 2013 tadpole shrimp study, told Live Science.
Studies of the fossil record suggest that species typically last between 500,000 years and 3 million years before they succumb to extinction or are replaced by a descendant, according to an article in the magazine American Scientist.
Earth is a challenging, ever-changing place, and everything from the temperature of the oceans to the amount of oxygen in the atmosphere is constantly in flux. And in this world of change, every living creature is running, swimming, slithering or flying to adapt and survive — or ends up dead.
All of this is about the survival of our species, but our civilization of over 8 billion could collapse well before conditions are sufficiently harsh to make all humans extinct.
Civilization has only thrived during the current unprecedented climate stability.
Looking at the history, clearly humans can survive climate that does really change “all the time”, but human civilization has only ever existed during this recent unique period of time with extremely little change in climate, with the previous shift of more than 1°C in global average occurring over 10,000 years ago, at around the start of the Neolithic which began between 11,000 and 10,000 years ago, when after humans after finally progressed over 300,000 years of homo sapiens being in the Paleolithic or “old stone age” as the climate continually changed into the Neolithic new stone age as the climate stabilised.
It is not just civilization that has been only existed during this recent unique climate stability, but the population of humans was also constrained. As noted above, despite humans having existed for over 300,000 years, it was not until just over 6,000 years ago that the human population over the entire globe exceeded 8 million. Throughout the entire first 300,000 years, the population never reached 1/1,000th of the population of 8 billion reached in late 2022.
While humanity in much smaller numbers can clearly survive in some places on Earth with climate from anywhere between +3.0oC above, to as much as -8.0oC below current levels, it seems likely that at the climate extreme, there may be places where we cannot survive. When climate is coldest, glaciation may cover off some areas. When it is warmest, sea levels can be 70 meters higher resulting in less land, and perhaps some of the hottest areas simply become too hot.
The knowledge that the “climate changes all the time”, rather than being a reason for comfort, would seem to be very good reason for concern that a change in climate will significantly reduce the parts of the Earth where that will allow people to exist outdoors.
Particularly concerning when considering the changes in climate typical throughout the past 400,000 years would be something we have not experienced for 12,000 years!
Can civilization survive a return to a “normal” level of climate change?
Looking at data for the past 2,000 years, what stands out is not climate change that was evident throughout the other 300,000 years of homo sapiens existence, but a continuation of the most recent over 10,000 years or remarkable stability. It has been like as if we as came out of the last glacial period whatever normally causes climate to change went into hibernation.
Looking first at the most recent time 2,000 years, which is the period for which we have the most accurate temperature data, reveals the “medieval warm period” may have been warmer in Europe, but not noticeably warmer globally, and while the “little ice age” was colder globally, it was colder by no more than at the extremes around -0.5°C. Up until the 20th century, the temperature was remarkably colder. This data makes the recent rise in global temperature really stand out.
Expanding the time window provides a different perspective.
Looking at the picture expanded to cover the last 24,000 years makes the magnitude of rise in temperature of the last 50 years almost nothing in compared with the temperature rise from 16,00 years ago to 10,000 years ago.
Yes, as pointed out in the article on Phy.org, the rate of the rise in temperature in the last 50 years is more rapid than any previous rise in temperature in the last 24,000 years, but the magnitude of the change we have seen so far is actually quite small, and there is no suggestion humans were behind the rise in temperatures 18,000 years ago. Nature can change temperatures by far more than this recent increase.
If we soon reach +2°C change, this will simply match the rise between 12,000 years ago and 11,000 years ago. While that rise of +2°C took around 1,000 years, perhaps more alarming is those +2°C of rise was part of an overall rise of nearly +8°C. Could this rise continue and reach +8°C again?
That the recent stable period of stable climate at current temperatures is unprecedented, at least during human history, becomes clearer when again looking at the further expanded time window to cover the entire time of homo sapiens.
But looking closely at the history of temperatures during the whole history of modern humans, it seems every previous extended period of relative temperature stability was followed by significant rise in global temperatures.
Each area circled represents, a time of a degree of temperature stability, and each period of relative stability was followed by a rise in temperatures. Historically, the pattern seems to be that the longer the period of stability, the bigger the following jump in temperature. Stable periods 1 and 3 were much shorter the current stable period and followed by temperature rises of only around +3°C, and periods 2 and 6 were the longest periods of relative stability and followed by rises of around +10°C. However, the only thing that can be taken from the data is that small rises in temperature tend occur when something is making temperatures swing back and forth, and any previous time a rise was not a “rebound”, the temperature rise has been significant. Note that the more “jagged” appearance of the graph towards the right simply reflects that there is greater detail to the most recent data.
Again, this current period of stability is different than any previous stable period. It is both at a higher temperature and shows greater stability than any previous event during the overall Late Cenozoic ice age. Perhaps these differences mean this time will be different, but there is certainly cause for concern.
Things could certainly be different this time, but previous events all suggest that once the temperature starts rising after being stable for as long as it has now, historically it has always risen by over +6°C. While that the temperature rise as recorded at the ice cores has on all previous been at a rate of around +1°C per century, these are ice-core temperatures, and it is quite likely ice-core temperatures rose much slower than global average temperatures.
Prior to 4,000 BCE, just 6,000 years ago, the entire human population had never exceeded 8 million. 1/1,000th of the population of today. With over 300,000 years for the population to grow, under constant changing climate, the population waxed and waned, but never approached the population of 8 billion that humans have managed to achieve in just 6,000 years under ideal climate conditions.
While so humans have proven through pretty much the coldest conditions outside a Snowball Earth event, it was not until an interglacial that civilization arose. It is unproven whether civilization would have ever arisen without this first extended stable temperature interglacial, but quite possible civilization could manage to adapt to a new glacial “full on ice-age”, although most likely with a vastly reduced population. What is less clear is the ability of creatures of an ice-age to maintain civilization, or even survive in a climate more like that of the dinosaurs.
Climate change humans have faced in the past would be devastating today.
Often the phrase “the climate is always changing” is frequently meant to imply that we humans have previously endured natural climate changes without significant impact. Yet the last major change of climate, the end of previous “glacial period” or ice age 12,000 years ago, did have an impact and would have an even bigger impact today because:
Previous changes to climate have had a significant impact and would have forced humans to relocate and migrate in ways that would be extremely difficult to replicate in the 21st century.
With 8 billion people now residing in locations all around the planet, should any significant areas become no longer suitable for human habitation it would cause an unprecedented crisis.
What happens when the ice age ends?
We are in the most recent of those blue blocks or “glaciations” from the 5 shown on the Wikipedia diagram above.
New Evidence We Are Entering An Ice Age Termination Event – EXPLAINED
Each glacial period represents a time when there are large glaciers on the surface of the Earth, and as can be seen from little of the diagram is marked in blue, and although we are in an “interglacial period” with less surface ice than the “full ice age” glacial period, we are still in one of the rare times when the Earth has any large areas of ice on the surface.
If we were to return to a “normal” non-glacial or “greenhouse” period, sea-levels would rise by around 70 metres and temperature could rise by +5.0°C or more.
As discussed in the video “New Evidence We Are Entering An Ice Age Termination Event“, there is evidence this process of warming may have already begun. Normal “non-glacial” periods are also called “greenhouse” periods, but considering how much of the timeline is not blue, the label “normal” does also seem appropriate.
However, while the huge change of Earth exiting an ice age and returning to “normal” could be happening already, for now, we are in the last of those intervals marked in blue, the current “Quaternary glaciation” of the Late Cenozoic Ice Age (Wikipedia).
How long would humans be expected to naturally survive on Earth?
While there are still up to 25 million years until “the flip” to the Earth hitting the path to the extinction of all life, looking at history, it is not like things will naturally be fine for 25 million years.
Even without a big dramatic change, or an extinction event, extinctions are still a part of nature.
Whether the current rise in temperatures continues and takes us out of what is perhaps surprising currently an ice-age as Dr Ben Miles predicts, or there is a return to our atypical time of climate stability for sooner or later, our time would naturally be up. One key reason why Earth scientist predict how long the Earth will support life, but not how long it would support humans, is it is just not the way of nature for a species like humans to hang around d for tens of millions of years.
The natural expectation, even ignoring the threat of an end to the Phanerozoic entirely, is that a primate mammal species like humans could expect to exist on Earth for an absolute maximum of 10 million years.
The oldest species of large mammal species still living today is the Okapi which is a member of the Giraffe family, and our relatives, Chimpanzees, Bonobos and Gorillas have all been on Earth for less than 2 million years.
Historical data reveals it is highly unlikely that any large mammal, humans included would naturally survive the entire possible 25 million years before “the flip“.
Warm-blooded animals: An additional vulnerability?
A key is “warmer than the environment”. Our body temperature is around 37°C, although over 20°C warmed than the global average, is not always higher than that of the current environment. Still our ability to handle temperatures over 37°C is quite limited, and generally requires low enough humidity for perspiration to be effective. Whilst ectotherms or “cold blooded” animals can more easily adapt to changing temperatures, we humans require our temperature to remain within a narrow range, and that can make us more sensitive to the environment. Our adaption of clothes has allowed us to handle colder temperatures than those in we initially evolved, but for higher temperatures we are fine indoors with air-conditioning, but always staying indoors is not ideal. Yet just a +5°C rise in temperature, and the number of occasions and locations when and where we need to remain indoors would skyrocket. At +10°C it would be catastrophic, yet if the “ice age” ends, the lack of reflective ice could soon enable such temperatures.
Can human society survive to allow us to become “the good guys”?
There is real reason to hope humans can break from the history of billions of years of climate change driven extinctions that has seen over 99% of all species that have ever existed already extinct. As humans have developed and entirely new form of evolution:
Humans can adapt and gain new capabilities, without biological evolution. As explained in the relevant webpaper, this “Accessorised evolution” is the key difference between humans and all other species, and gives humans not only the ability to adapt and evolve our capabilities whilst remaining the same biological species, it can even give humans to not just survive climate change, but perhaps even control climate change.
As the first species able to evolve and enhance our capabilities through tools that evolve from generation to generation, human “accessory” technology has reached the point where we are able to “tweak” the Earth’s climate, and potentially prevent either nature or ourselves “poking the bear” to the point where natural positive feedback produces significant climate change.
So far, we have demonstrated an ability to raise CO2 levels, and the technology to produce synthetic fuels could in theory be used to sequester CO2 and lower CO2 levels. While we not only have the technology but also the economy to raise CO2 levels, but while we have the technology to sequester CO2, the economics for lowering atmospheric CO2 levels if required are, so far, more questionable.
We know that volcanoes or meteors can “poke the bear“, and perhaps human emissions can also “poke the bear” of climate change, but that also would mean humans can, to some extent, influence climate, and therefore, potentially block natural events from “poking the bear”. Realistically, while our current capabilities to block natural climate change may not be up to the task, given time, we could get better.
No previous species of human, nor even any other large species of mammal has survived for 25 million years. Without the ability to at least delay or limit the impact of natural climate change, neither would we.
Unless we can block it, sooner or later, either us humans or some natural event will “poke the bear” and climate change will wake from hibernation.
If humans could prevent climate change from disruption society for even another thousand years, it could be all we need to be able to become a multiplanetary society.
At the other extreme, the worst humans could possibly do is themselves is themselves induce climate change.
While some suggest human induced climate change is an “existential threat”, as humans can only induce climate change whilst society functions, and human society is particularly vulnerable to climate change, the threat from human induced climate change alone is really for historically quite a small change in climate.
A bigger threat is that humas could “poke the bear” and trigger natural climate change, that in the most extreme scenarios, could see climate change continue after human society has collapsed and even cause many other species, particularly other warm-blooded animals, to become extinct.
Overall, while there are still as many as 25 million years before “the flip” that begins the process of making all life on Earth extinct, if humans were in that worst possible scenario, to launch the extinction process 25 million years earlier, than nature, that would still at worst on mean a 5% reduction the time window for “visible life”, which is very little compared to the potential for humans to extend the window for chosen species of Earth.
Not all life ends at once, but in mostly reverse order of arrival.
While Earth has had a remarkably long-time supporting “slime” of primitive life invisible to the naked eye, it is only during the most recent 1/10th of the time that Earth has naturally supported a species like humans. If a spacecraft were to arrive on Earth over 500 million years ago, humans on board would need a spacesuit to survive on the planet. Arrive on Earth 100 million years from now, and you would again need a spacesuit. However, at both these time, Earth would be home to some more primitive life.
We are on a 4.5 billon year old planet, where until the past 0.5 billion years, a human would need to wear a spacesuit to survive because there was no oxygen, too much radiation and it was too hot. But that is the past, and we live in the present with an ozone layer, an ideal level of oxygen for us to beath, and temperatures that enable us live almost anywhere on the planet. The question for the future, is how much longer conditions will be so suitable for us humans given the planet is about to switch from the cooling phase to warming phase.
How much time remains for “visible” complex life like us?
So how long does Earth have until the planet is swallowed by the sun? Expected time of death: several billion years from now. But life on Earth will end much, much sooner than that.
Earth will become unlivable for most organisms in about 1.3 billion years due to the sun’s natural evolution, experts told Live Science.
No, that the Sun will take 5 billion years to explode does not mean all is well until then, and that it will take 1 billion years of rising temperatures makes the oceans boil does not mean we will be fine until then either.
Here are the steps to realising how little time there is left for life of the Phanerozoic.
Not 5 billion years, because what happens to Sun is progressive.
Most people have heard that in around 5 billion years, the Sun will “explode” in size to nearly engulf the Earth, and clearly, life on Earth can’t survive that.
The catch is, that it is not like everything is fine for 5 billion years with nothing changing and then suddenly the sun explodes.
Last extremophiles on a barren planet extinct in 1.75 billion years.
The 1.75 billion years is when the last life of any form, the last extremophiles, finally becomes extinct from the very last location on Earth where they could exist.
1.75 billion years sounds long enough…but imagine how barren the planet must be for even those very last extremophiles to finally also be unable to survive anywhere!
Again, the catch is that instead of the Earth being perfectly habitable for nearly 1.75 billion years, and then suddenly some disaster strikes, Earth is becoming less and less habitable over the entire 1.75 billion years.
In fact, conditions for life began deteriorating 500 million years ago, and the Earth today only supports 1/2 the total life the Earth supported 500 million years ago.
Procaryotes: 1.5 billion years left.Eucaryotes: 1.2 billion years.Simplest plants: 750 million yearsHardiest animals: 600 million yearsModern plants: 350 million years.Insects: 200 million years.
Progressively life is restricted to simpler and simpler forms, mostly becoming extinct in reverse order to their first appearance on Earth.
1.5 billion years remain for procaryotes that first appeared 3.5 billion years ago.
1.2 billion years remain for eucaryotes which first appeared 2 billion years ago.
750 million years for the simple plants, which first appeared around 470 million years ago.
600 million years for the most robust “complex” animals that first appeared in the Cambrian explosion.
400 million years for the most basic modern plants, and for insects with both first emerged between 350 and 450 million years ago
350 million years for insect for insects.
200 million years for flowering plants which only emerged first emerged around 140 million years ago.
Warm blooded animals with body temperatures evolved to thrive during the
And humans and their ancestors who first appeared only within the last 3 million years of the glacial “Ice age” … could survive for 25 million years.
And human complex societies that first appeared within the last 10,000 years…….?
The risk for humans and human society is that even within the Phanerozoic, .
How climate tolerant are humans?
We humans could develop technology that prolongs our existence, either by managing to delay climate change or become a “multiplanetary species“, but fundamentally we are an ice-age species on a plnaet where icer-age are not normal, and things are about to start heating up;.
Without technology, in a best-case scenario, the last humans could perhaps exist as small group on what is currently the Antarctic even 50 million years from now, but humans spread all across the planet like today, around 25 million years for support of even 1 billion humans at a time would be more realistic optimism. While for life on Earth that has existed for billions of years, 25 million years is nothing, but for us humans, 25 million years is like an eternity.
Climate aside, the window for human society with modern science & technology.
Would we go back to life without modern medicine?
In 1900, life expectancy was just 32 years! No, this does not mean everyone died at around the age of 32, as the idea that life expectancy numbers from the past reveal shorter human lifespans is just confusion arising from averages. The reality is that in the past, around 50% of all people died as children. Average out the 50% who died as children at an average age of 5 years and the other 50% dying at an average age of 70 and you get an overall figure of 72.5 years. While it is not full story, it is close enough to understand why your grandparents and great grandparents probably lived to around the age of 70 despite that life expectancy for someone born in 1900.
Being born much before 1900 meant being born into a family where, globally, most children died. From an era without smallpox and where people get tetanus shots it seems hard to imagine, but I had appendicitis in early teens, so I can see how in earlier times I would have died.
Parents losing half their children made a far more tragic world. Beyond the loss of life, even simple things like a world where women had to have far more babies made gender equality more difficult, are hard to imagine today.
I don’t think people would suggest we should have avoided reducing infant mortality in order to avoid having the population explosion.
The near elimination of child mortality triggered a population explosion that has threatened our existence but presents nothing like the challenge of the population explosion that will result when achieve the near elimination of elderly mortality. It may today sound like science fiction that we could eliminate ageing, but in reality, it seems almost certain that this will be possible within the next few centuries, that is, provided civilization continues to enable progress. However, when people don’t automatically die at any age, then either having children is reduced to being reserved for when someone dies, or we have another, far more problematic population explosion.
Humans were able to limit and end the population explosion resulting from the change to most people surviving by dropping family sizes, but if everyone born could stay alive almost indefinitely, the only path to stable population would be almost zero children, or continually finding new space for people to live. It is very possible that within around 500 years, humans could need to expand beyond Earth.
While 500 years sounds a long time for establish at least one “Earth 2.0”, it is far more complex than most imagine, but if we can manage such expansion, from that point natural climate change on Earth would be a different type of problem.
In the meantime, we need solve the environmental factors that present an existential threat to, although probably not all life on Earth, but at least to a society capable of tackling big picture threat to all life on Earth.
It is not clear yet whether natural climate change or largely eliminating elderly mortality will be first to present an environmental threat, or whether other threats we humans create for ourselves emerge first, but there are some problems to tackle. What makes natural climate change different is that it will happen even without humans playing a role, and could happen anytime, most likely in the next 10,000 years according to the US Geological Survey, or perhaps even more dramatically even ending any form of ice-age within the next 100 as suggested by Dr Ben Miles. Statistically my house will not burn down even in the next 100 years, but still, I take out insurance every year. Should we be taking out insurance against natural climate change, or instead “poking the bear” by making our own changes?
Is life almost entirely “Just slime” or is that not what life means?
Phanerozoic life: The meaning in normal conversation of the word “life”.
I suggest for most of us, when we think of life, we think mean not the almost indestructible invisible microorganisms that we must kill to sterilize a needle or medical equipment, but species we may use that medical equipment to save.
Yet in the universe, the Earth historically and still today, and even inside our bodies, most life is microscopic single celled organisms, and very different than what most people picture when we think of life. I recall a joke about how the Dali Lama when driving a car seems to be always swerving and the punchline was, he was avoiding hitting and killing tiny bugs. Even in that joke no one even pictured the far greater amount of microscopic life. Partly because it is hard to imagine singled celled organisms which seem more like replicating chemical structures as having “karma”. Imagine a doctor in a hospital after being told he had saved a life declaring “Yes, I did manage to save one life, but unfortunately I had to cause the death of billions of bacteria”.
In some ways, we see less difference between “just chemicals” and the simplest procaryote singled-celled life I refer to as “just slime” than us and these single celled procaryotes.
Yet discussions about whether life can or will survive, very often ends up misleadingly being about these single-celled organisms. It really depends on what life is taken to mean.
It may even be that life only ever begins in locations like deep sea vents at temperatures hostile to complex life like us.
Is “just slime” almost all there is out the in the universe?
While astronomers said there were about 20bn Earth-like planets in the Milky Way galaxy, “so we might expect life to be everywhere”, “almost every biologist I speak to says, ‘Yes, but all it will be is slime at best.’ We live in a violent universe and the idea you can have planets which are stable enough to have an unbroken chain of life might be quite restrictive.”
Most people have heard of the “Goldilocks Zone” as the zone where conditions are “not too hot or too cold”, but from my casual surveys, the term is misleading and quite misunderstood, with the most common response to what it means being “the zone where the Earth is and where it is suitable for us to live”, when it does not mean that at all.
For the first 4 billion years, all that lived on Earth was “just slime”.
Even today more than half the total biomass is made of single celled organisms too small to see individually with the naked eye. Even our own bodies contain 10x more non-human bacteria cells than human cells, although these simple cells are smaller so by mass, so we are still mostly human.
While the Earth has supported single celled life since almost the beginning, it is only in the Phanerozoic Eon which is the most recent 10% of Earths life, that Earth has been home to complex multicellular organisms like us, or any of the plants and animals we can actually see as individual living things.
Even today, life one Earth is “just slime”.
First the first 4 billion years the only life was singled celled primitive life, and even today over half the biomass of all life on Earth is made of organisms we can’t see with our own eyes. While it a biomass of is around 3.8 Gt of procaryote/eukaryote life to 2.1 Gt of complex multicellular life, once you consider the vastly higher number of individuals of the smaller celled animals per unit of biomass, it becomes clear well over 90% of organisms on Earth today are just single-celled.
Even human bodies contain more “just slime” cells than human cells.
Even our own bodies contain 10x more non-human bacteria cells than human cells, although as these simple cells are much smaller than human cells, so by mass, so we are still mostly human.
“Just slime” can live in extreme environments.
Earth is a planet where life began almost immediately and being in the Goldilocks zone of our star, nature inherently supports life. That is all true, but “life” is not what people think of as life.
Even complex life such as tardigrades can survive down to 0.01 K (−460 °F; −273 °C) (close to absolute zero), and up to 420 K (300 °F; 150 °C), but how resilient life can be.
Organisms exist in every part of the biosphere, including soil, hot springs, inside rocks at least 19 km (12 mi) deep underground, the deepest parts of the ocean, and at least 64 km (40 mi) high in the atmosphere.[96][97][98] For example, spores of Aspergillus niger have been detected in the mesosphere at an altitude of 48 to 77 km.[99] Under test conditions, life forms have been observed to survive in the vacuum of space.[100][101] Life forms thrive in the deep Mariana Trench,[102] and inside rocks up to 580 m (1,900 ft; 0.36 mi) below the sea floor under 2,590 m (8,500 ft; 1.61 mi) of ocean off the coast of the northwestern United States,[103][104] and 2,400 m (7,900 ft; 1.5 mi) beneath the seabed off Japan.[105] In 2014, life forms were found living 800 m (2,600 ft; 0.50 mi) below the ice of Antarctica.[106][107] Expeditions of the International Ocean Discovery Program found unicellular life in 120 °C sediment 1.2 km below seafloor in the Nankai Troughsubduction zone.[108] According to one researcher, “You can find microbes everywhere—they’re extremely adaptable to conditions, and survive wherever they are.”[103]
A full life cycle3, rather than only survival, can only occur to our knowledge in conditions when water is liquid, which is why the Goldilocks zone is generally considered to need temperatures to at least at times exceed 0°C (32°F), and while with sufficient pressure liquid water can exist up to 374 °C (705 °F), for planets close to the size of the Earth, temperatures usually below around 150°C (302 °F) seem a more realistic upper constraint .
More specific terms: From including “just slime” to only complex life or mammals.
With the term “Goldilocks” zone meaning conditions for any form of life, it may be useful to also have terms for the more restrictive conditions for “life we can see” as opposed to conditions that only support single celled organisms.
Geologists use the “Phanerozoic eon” for the time of life beyond “just slime”, with the “Phanerozoic” coming from the Greek for “visible life”.
Whilst there is some recent evidence that there may have been some examples of complex life even before the Phanerozoic Eon, it is almost certainly this was possible because there would have been small parts of the globe providing Phanerozoic conditions long before those conditions were sufficiently prevalent to enable the Phanerozoic eon. But what are “Phanerozoic conditions”?
Phanerozoic conditions are, logically, the conditions required by “complex” life of multicellular organisms visible to the naked eye, that constitute what most people think of as “life”. This is not an official term, but when used on this website, Phanerozoic conditions include the presence of oxygen, as there are no known multicellular organisms that rely exclusively on anaerobic respiration for their entire lifecycle. As “but no eukaryote appears to be able to complete its life cycle above ∼60 °C and most not above 40 °C“, I will also include “average temperatures lower than ∼40 °C” as another condition, since it appears only single celled eukaryotes are able to complete their lifecycle at over 40 °C.
The thermal limits to survival are well documented for many types of organisms, but the thermal limits to completion of the life cycle are much more difficult to establish, especially for organisms that inhabit thermally variable environments. Current data suggest that the thermal limits to completion of the life cycle differ between the three major domains of life, bacteria, archaea and eukaryotes. At the very highest temperatures only archaea are found with the current high-temperature limit for growth being 122 °C. Bacteria can grow up to 100 °C, but no eukaryote appears to be able to complete its life cycle above ∼60 °C and most not above 40 °C.
Few multicellular life forms are anaerobic, since only aerobic respiration can provide enough energy for a complex metabolism. Exceptions include three species of Loricifera (< 1 mm in size) and the 10-cell Henneguya zschokkei.[23]
The next term I find it would be useful to have, is a label term for the conditions that allow humans to exist. Humans require oxygen levels within well researched but surprisingly narrow limits of between 19.5 and 23.5 percent, large areas of exposed land as opposed to entire globe covered with oceans, low levels of ionising radiation as currently available due to Earth’s ozone layers, and temperatures between around 0°C and 40°C. Temperature is the one that could be the most debatable, as given humans are an “accessorised species“, it becomes debateable what level of accessories to deal with temperature extremes should be considered in determining the temperatures suitable for humans. While the heat side of this question is becoming a well-researched topic with facilities including:
Less research on cold is considered as this is not the current threat. Also, different studies assume “accessories” are available to deal with temperature extremes. Studies focusing on early humans consider only what clothing can be assumed to be available, studies on the future can assume better clothing, shelter and other technology. Generally, most papers and other resources do not regard reliance on air-conditioning to be included, but most often do assume people will access have modern clothes which provide better insulation than humans have had during most of their existence, and access to housing which, even without “air-con” can provide shelter.
With the right technology or accessories, clearly humans can survive a wide range of conditions, so there is no universal answer to temperature limits, but given just how widely temperatures on Earth can change over time, the range of an average between 0°C and 40°C over the longer term seems quite widely accepted as conditions for humans.
“The data shows that remdesivir has a clear-cut, significant, positive effect in diminishing the time to recovery,” Dr. Anthony Fauci said at the White House
Covid-19 has made many phrases like ‘flattening the curve’ become part of News broadcasts, political announcements, and even everyday conversations. But, what is the curve?
Media reports, and government data, repeatedly presents ‘numbers of Covid-19 cases‘. However, the data presented is not the number true count of all cases numbers,
blue highlighter, most of the time the Earth is not in any level of ice-age.
