Synopsis: All planets that support life, only do so for a relatively brief time.
On a timeline mapped to a year, for only three months would there be any oxygen in the air on Earth for humans, and for only one month living things on land. The time since peak life and the dinosaurs to now would be just over two days, and the entire time homo sapiens have existed maps to less than one hour.
It is believed that both Venus and Mars could have at one time also supported life, but the window for life on both seems long closed.
From humanity’s perspective, we have only just begun, and, without some disaster, the planet will still support us for a few million more years. However, from the perspective of the 4 billion years there has been life so far, the end is very near, and when projected onto an annual calendar means as little as 2 more days left on the calendar before the Earth no longer naturally supports life. This is a dying planet.
Key Timeline Observations & Key Interesting Events.
The timeline is based on the life of the Sun from its formation as a ‘faint young sun‘, through to the end of its life as a ‘main sequence’ star when it will become so large as to either engulf, or almost engulf the Earth. Time, as mapped onto a year, and the actual dates are available in the table of events below.
Although the early Earth supported very primitive life in the oceans since soon after formation (the orange highlight on the calendar), ‘life as we know it‘, the yellow highlight section representing the Phanerozoic era, and life on land (the green highlight on the calendar) are both very recent in geological terms. Very early animals like trilobites, only came into existence in the Phanerozoic era, in the most recent 12% of the Earth’s life.
Reality, it is only recently that the Earth was able to support life as we know it on the surface and Earth cannot support life for much longer, with the amount of complex life already in decline. Temperature regulation while orbiting the Sun with its the slowly, but perpetually, increasing radiation relies on the continual reduction of CO2. We are running out of CO2 to reduce, and we already need to be at less than 0.05% to keep things sufficiently cool. Within as little as 25 million years, either CO2 levels become too low to support plant life at our temperatures, or the Earth becomes unbearably hot as happened with Venus.
To humans who have not even began the first civilizations even 25 thousand years ago, 25 million years is an almost unimaginably long time, but it is such a short time for live overall, that it is less than 2 days when projected onto the solar system calendar.
On the one-year timeline, we humans, our pets and other current complex forms, all need to find another home by the end of tomorrow, and that is without anthropogenic climate change, or any problems created by humans.
Some key points:
- Life on Earth began early, without any oxygen present, and evolution was initially very slow.
- Cyanobacteria: The first photosynthesis, and first phytoplankton. Still, today, phytoplankton are more important than all forests in absorbing CO2.
- It took around half the time there has been life, to evolve to multicellular life, as Evolution started very slowly.
- It took almost 3 billion years before even single cell animals first appeared on Earth.
- Life as we know it, and organisms that could be seen without a microscope, is relatively recent, and confined to the Phanerozoic era, or yellow highlighted month of June on the timeline.
- Peak life at over 500,000 years ago, with the total amount of life falling ever since.
- The Brief Burst of Life on Land following the ozone layer creating a radiation shield.
- Thermal Runaway: When further reductions to CO2 are no longer possible, life will end, and far earlier than most people assume.
- Eventually the Sun will expand to eventually become briefly a red giant before collapsing to become stable as a ‘white dwarf‘.
- Note that the Sun is a ‘Yellow Dwarf star‘ that happens to be white, which is confusingly very different from becoming a ‘white dwarf‘.
First Life on Earth Began Early: But it was not life as we know it.
Initially, life was only possible under the sea due to radiation the atmosphere.
Earth was originally hostile to life as we now know it.
Despite this, as time progresses, new evidence of early life continues to emerge:
- Oldest fossils ever found show life on Earth began before 3.5 billion years ago
- Oldest Evidence of Life Found in 3.95-Billion-Year-Old Rocks
- Earliest Evidence Of Life On Earth ‘Found’
Life began within around 500 million years of the Earth forming around 4.5 billion years ago, which may sound like life took a long time to begin, but considering the Earth was formed as a result of a sequence of collisions, things would have taken quite some time to become even close to stable.
- Early Earth’s Atmosphere Was Surprisingly Thin
- We May Have Seriously Underestimated How Hostile Conditions on Early Earth Were
- What Was it Really Like on Early Earth?
First life had to form in the oceans or at hydrothermal vents, given that land was inhabitable due as the original atmosphere was not breathable and provided no protection from cosmic rays and other space radiation.
Evolution started slowly: It took 4 billion years for life to become abundant.
Although life began quickly, you would need a microscope to be able to see individual living things.
Given how quickly life arose, it seems surprising that it took another 2 billion years to have even single celled organisms, and 3 billion years to get to multicellular organisms. For 3/4 of the time there has been life, all life was single cell life, and there were no animals at all. Evolution was slow to get started!
Complex life on land took 4 billion years to be possible.
Firstly, it had to wait until just over 500 million years ago for the atmosphere to develop enough oxygen to provide the ozone layer and protection from cosmic rays and other space radiation to allow complex life to even exist on the surface, without wearing a spacesuit.
Even then, plants could not grow until there was soil and persistent moisture before plants and then animals could colonise the land.
It is also in the Silurian [Silurian from the end of the Ordovician Period, at 443.8 million years ago (Mya), to the beginning of the Devonian Period, 419.2 Mya] that we find the first clear evidence of life on land. While it is possible that plants and animals first moved onto the land in the Ordovician, fossils of terrestrial life from that period are fragmentary and difficult to interpret. Silurian strata have provided likely ascomycete fossils (a group of fungi), as well as remains of the first arachnids and centipedes.
Berkely: Life of the Silurian
Photosynthesis: Turning CO2 into O2 is not about plants.
Photosynthesis started way before there were plants.
Humans could not exist, if not for fact that life long ago converted almost all of the CO2 in the atmosphere into oxygen. Yet, given that ‘life as we know it‘ has existed only in the ‘yellow’ month of June on our calendar, it clearly cannot have been plants was not plants that converted all that CO2 into oxygen.
It turns out, we are not as reliant on modern plants for oxygen as could be assumed.
We tend to think of the world’s rainforests as the ‘sinks’ that that convert CO2 into oxygen and save use from the evils of high levels of CO2. It is a great story, and while the rainforests are essential to maintaining ecosystems that are essential to our existence, almost all of the oxygen in the atmosphere was produced by organisms that existed way before pants as we know them. Even today, most photosynthesis is done by phytoplankton, not plants.
The first photosynthesis: From 3.4 billion years ago.
Fossils of what are thought to be filamentous photosynthetic organisms have been dated at 3.4 billion years old,[4][5] consistent with recent studies of photosynthesis.[6][7] Early photosynthetic systems, such as those from green and purple sulfur and green and purple nonsulfur bacteria, are thought to have been anoxygenic, using various molecules as electron donors. Green and purple sulfur bacteria are thought to have used hydrogen and hydrogen sulfide as electron and hydrogen donors. Green nonsulfur bacteria used various amino and other organic acids. Purple nonsulfur bacteria used a variety of nonspecific organic and inorganic molecules.[8]
Wikipedia: Evolution of photosynthesis
Cyanobacteria and other phytoplankton: Still our main source of oxygen today.
Cyanobacteria (at this time, Wikipedia has some errors on this topic), also known as ‘blue-green algae took over as the lead oxygen factory from around 3 billion years ago. While it takes a microscope to see individuals, water becomes distinctively coloured. Early cyanobacteria had no cell nucleus and are one of the simplest forms of life on Earth but performed most of the all-important task of oxygenating our atmosphere.
Although today there are also other types of phytoplankton, these together make up the most important factory for converting CO2 into oxygen.
Despite all our likely justified fears of the impact of deforestation, the ability of life to turn CO2 into oxygen does not appear to have ever depended on photosynthesis by land plants.
Phanerozoic and Peak life on Earth: 540 Myr ago.
The Dawn of the Phanerozoic Era: Peak life on Earth
540 million years ago the dawn of the Phanerozoic era began, marking the beginning of life as we know it. Phanerozoic translates as ‘visible life’.
‘Peak life’ occurred very soon after the beginning of the Phanerozoic, as can be seen from graph here, with levels having now in the present having fallen to half those levels of around 500 million years ago.
From that ‘peak life’ level, that total amount of all life will continue to fall until the increased Solar radiation can no longer be offset by reductions in CO2 levels.
While CO2 is the villain of global warming today, more CO2 does help plants grow and photosynthesise better, which is one reason plants grow better in a greenhouse. The better plants can grow, the more plants, and the more animals that can eat those plants, so therefore, the more total life.
It is necessary for CO2 levels to keep slowly falling to counter every increasing radiation from the Sun, but the downside is the ever-falling levels of CO2 result in an ever-falling total amount of life on Earth.
Land Plants: Not the main CO2 sequestration factory.
Land plants were not even present during the first 3 billion years of life, with green plants on land only known to exist from around 550 million years ago.
This means that almost all of the oxygen in the air was produced before green plants on land even existed.
Only a brief burst of life on Land.
On the ‘annual calendar’ life on land is possible for only three weeks. Life on land becomes possible in early June and becomes no longer possible before the month is over. The entire time phytoplankton and are continually transforming CO2 in the atmosphere to oxygen, at a pace regulated by rate of increasing heat arriving from the Sun. If the CO2 and greenhouse effect is reduced faster than the Sun warms, the Earth would freeze, if the process is too slow, the Earth warms.
The brief window for life on land is the result of their only being enough to oxygen produced from the CO2 to allow ozone to block deadly radiation reaching the Earth’s surface, at the point with further reduction in CO2 becomes impossible, ending the time temperatures on Earth can be kept in check despite the increasing heat arriving from the Sun.
For the entire duration of life on Earth, photosynthesis has been reducing CO2 level, which has reduced the greenhouse effect, which has compensated for the ever-increasing solar radiation from the Sun. However, we are running out of CO2, limiting our ability to keep further reducing CO2.
Reduce CO2 too much further and plants can no longer continue photosynthesis, stop reducing CO2 and we can no longer adjust for the ever-increasing solar radiation. As little as 25 million years remains, and although it is possible life could survive longer, it is inevitable that the ever-increasing solar radiation will make the Earth too hot for life.
Humans: from 300,000 years ago?
The oldest Homo sapiens fossils that anthropologists have found thus far date to around 315,000 years ago. That means we can say that modern humans are at least that old. But our lineage likely extends further back in time — we just don’t have the fossils to prove it.
DNA evidence drawn from comparisons of different human genomes, as well as those of close cousins like Neanderthals and Denisovans, put the split between the three groups at at least 400,000 years ago. So it’s possible that H. sapiens is over half a million years old.
Discover.
Past Extinction Events: How have we survived this far?
Setbacks happen.
Not only has the earth only been home to life as we know it for a small minority of time, and able to support life on land for an even shorter time, but even in those small windows, there have been catastrophes that resulted in mass extinction for a large percentage of all life. How close has life of earth been to total extinction in the past, and how is the inevitable end for life on a planet orbiting an ever-changing star?
The Oxygen Catastrophe and other early extinction events.
Normally, only extinction events during relatively short Phanerozoic era (yellow on the timeline) are counted as official extinction events, but this brief window is the era of ‘life as we know it’.
Prior to the Phanerozoic era, what life did exist was very simple, and you would think therefore very robust. There may have been countless extinction event, but it is hard to be certain how many, as this very simple life did not have bodies that would result in any fossil record, so any number of mass extinction events could have gone unnoticed.
We are aware of at least one mass extinction, the Oxygen Catastrophe resulting from a planet previously without free oxygen experienced a rise in the amount of oxygen level. This can be inferred to have caused a mass extinction as oxygen would have been poisonous to most previous forms of life, proof is difficult.
Snowball Earth events are also hypothesised to have occurred prior to the Phanerozoic era and would have also caused mass extinctions, but again the lack of fossil records makes certainty problematic.
Meteors and volcanic activity would both have almost certainly triggered may mass extinction events, but all we know is that somehow, life made it through.
Phanerozoic Era events: Event in the yellow, with far more to lose.
Life did make it through to the Phanerozoic era: the surprisingly recent explosion of complex life. At 540 million years ago, at the beginning of the current month on the 12-month calendar projection, this era marks the earliest date of ‘official’ extinction events, as this is when there is sufficient variation on types of life, and sufficient fossil records, to be able to record how many species were affected.
We are aware of major mass extinction events in the just over since the start of the start of the Phanerozoic era 540 Ma (Ma = million years ago), which means, on average, one every 100 million years:
- Ordovician–Silurian extinction events: 440-450 Ma, volcanic triggered, most likely global cooling.
- Late Devonian extinction: 360-375 Ma, unclear, but possibly volcanic triggered cooling.
- Permian–Triassic extinction event: 252 Ma, the largest extinction event of the Phanerozoic era, generally agreed as triggered by warming from increased CO2 arising from volcanic activity.
- Triassic–Jurassic extinction event: 201 Ma, source not clear, but could be an asteroid that this time helped the dinosaurs become dominant.
- Cretaceous–Paleogene extinction event: 66 Ma, what perhaps one asteroid gave, another took away, although dinsoausrs were already in delcine, potentially through volcano induced climate change..
This makes 5 mass extinction events in the past 500 million years, or one event every hundred million years, and there could easily have been a total for 40 times number in the past, and life has survive them all.
Fortunately, even the worst mass extinction event we know of, the Permian-Triassic event, meant the end for as many as over 80% of all, but still only just over half, 57%, of all families of species were completely wiped out.
The Fossil Fuel Extinction: Potentially number 6 of the Phanerozoic era?
For whatever reason, the world is currently experiencing what could count as another mass extinction.
WASHINGTON, D.C. (October 12, 2022) – Monitored populations of vertebrates (mammals, birds, amphibians, reptiles and fish) have seen a devastating 69% drop on average since 1970, according to World Wildlife Fund’s (WWF) Living Planet Report 2022. Populations in Latin America and the Caribbean have fared worst, with an average decline of 94%. Global freshwater species have also been disproportionately impacted, declining 83% on average.
69% average decline in wildlife populations since 1970, says new WWF report
Bad as it sounds, most species are endangered rather than extinct, so they are still saveable. The problem is despite all the discussions, global emissions still continue to rise. True nett zero by 2050 may happen in some a few countries, the China and India are not even aiming for nett zero at this time.
All species lost is not caused by global warming, and not all species loss will on a successful transition away from fossil fuels alone.
While it does seem inevitable that global temperature will rise by at the very least 3°C, and this will at the very least be extremely ‘inconvenient’, it seems inconceivable that this current human driven ‘extinction event’ will be left continue to the level of even the smallest of the big 5 above.
Future Extinction Events: Has life has remarkably little time left?
Sooner or later: an 100% extinction event is a certainty, and the only question is when.
At some point, the ultimate extinction event awaits. Our star will end its main sequence lifetime, and life on Earth cannot survive.
It is often explained how the Sun will, as the end approaches, expand to a size so large it could even engulf the Earth, and if there was life at that time, it would surely fry. Looking more closely, it is clear that the Sun will continue to increase the heat it sends our way as it transforms from initially fusing only hydrogen, to running low on hydrogen and instead fusing heavier elements, and it will get far too hot on Earth well before the Sun at end of its life as a main sequence star.
You may have heard of the ‘goldilocks zone‘. The distance from a star that is ‘not too hot’ and ‘not too cold’. In reality, for any star, the zone keeps moving as the star increases its heat throughout its life.
The Earth is now at the hot, very edge of that zone, as the Goldilocks zone continues to move further away, and quite soon on a geological scale, Earth will be outside the zone.
The good news, on a human timescale, the increasing heat from the Sun is insignificant. At the very least we have 25 million years left before our ultimate extinction event.
Extinctions leading up to thermal runaway: But not all life need be extinct at once.
Life could disappear in reverse order to arrival.
It is not like one day, the Earth would be like it is now, and the next, everything has changed. That could happen with another meteor or asteroid, but not with Solar warming which, unlike current global warming, does arise from the very gradual increase in solar radiation that happens over millions of years.
Since life began, life has been reducing CO2 levels on Earth from the initial mostly CO2 atmosphere, down to today’s level, with CO2 at less than a mere 0.05%. Soon on geological timeframes, temperatures on Earth will start to rise as CO2 levels will be too low to be able to continue to be reduced.
Life has time to evolve and relocate as the Earth warms. Currently, at least on land, there is little life at the poles, and far more at the equator. This could reverse as the Earth warms. Then there are extremophiles, proving life can survive “extreme temperature, radiation, salinity, or pH level.” (Wikipedia)
Some of the earliest known lifeforms would qualify as extremophiles, and it is highly likely so will some of the last.
A disturbing Eureka Moment: As little as 25 million years left for humans?
I first realised inability to keep reducing CO2 to compensate for increasing solar radiation, could be a limitation for life on Earth, while exploring natural climate change back in 2019.
However, that ‘eureka moment’ was initially based on quite simplistic calculations. The initial estimate was for about 70 million years for a very broad impact, and perhaps a little as 25 to 50 million years, before humans might be threatened. This was quite a surprise, as all I had seen previously, was projections of how the Sun would become a red giant around 5 billion years from now. Five billion years is a lot less threatening than perhaps as little as 25 million years, even though for one individual, both timeframes are so long they are hard to imagine. Even if my projections were seriously wrong, I had still found something new to me. But this still needed support from peer reviewed papers. The papers Lovelock and Whitfield, and Franck et al, as discussed in the next two sections, confirm that scientific consensus does exist that the amount of life on Earth has been on a path to collapse since peak life around 500 million years ago, and is expected to end on a timeframe consistent with my findings. However, the exact time range for humans, or what humans evolve into over such a long, is impossible to predict with any certainly. The changes will make life progressively more difficult, and even impossible for the humans of today within 25 million years, but perhaps with an artificial environment the radically smaller biosphere could support a very small population of human for even 100 million. However, evidence confirms, counting on any more than 25 million years, would be ‘courageous‘.
First Confirmation of a soon ending biosphere: Lovelock and Whitfield 1982.
Not surprisingly, if I could figure out the general principle, so could many others. The first paper as far as I am aware was by Lovelock and Whitfield in 1982:
Here we discuss possible links between the biological and geological control mechanisms. It is clear that whatever the mechanism, atmospheric CO2 is now close to its lower limit of partial pressure, so the biosphere may soon, in geological terms, be exposed without protection to the predicted progressive increase of solar luminosity.
Lifespan of the biosphere: Lovelock and Whifield.
In short, the Lovelock and Whitfield original assessment is for the biosphere will end in approximately 100 million years. That is the end for even the cockroaches, tardigrades and even most primitive single cell organisms. The threat of the biosphere ending in 100 million years sounded an alarm that perhaps 25 million years for humans was being too optimistic. All predictions are that the most complex and recent life, will be first go. More research was needed for a clearer picture on a safe time for humanity.
OK, doctor google, or better, S. Franck et al, how long have we got?
The best paper I have found on this topic is “Causes and timing of future biosphere extinctions”, by S. Franck, C. Bounama, W. von Bloh in 2006, and available here, and also here.
Further research. both in this and the preceding papers, pushes the end date for the biosphere out to possibly 1.5 billion years, but with all multicellular life ending which includes even the cockroaches and tardigrades within a maximum of half of that time. Much of the expanded time frame is allowance for adaption through evolution, and the possible persistence of extremophiles. What is clear is, that complex, Phanerozoic era life started falling from peak levels from around 200 million years ago and will be falling for even each of those next 25 million years.
Realistically, even in those next 25 million years, the carrying capacity of the Earth for mammals and other vertebrates will fall significantly, and likely fall quite noticeably.
For these charts from the Franck et al paper:
Case 1, (a) Evolution of global surface temperature (solid
green line). The green dashed line denotes a second possible evolutionary path triggered by a temperature perturbation in the Neoproterozoic era. The coloured area indicates the evolution of the normalized continental area according to Condie (1990). (b) Evolution of the cumulative biosphere pools for procaryotes (red), eucaryotes (green), and complex multicellular life (brown).
The result is almost a reversal of evolution.
However, the Franck et al paper does not attempt to predict when humans as we are now would become extinct or investigate nor rule out thermal runaway occurring before the predicated end date, accelerating the process. Both these points are beyond the scope of the paper, and predicting when humans, a species that evolved only less than 0.5 million years ago, and from a biological point of view would seem unlikely still exist in the current form even 10 million years from now, would be straying from pure science, and highly controversial.
What will happen to humanity over the next 25 million years humans beyond existing in a would whet the total amount of life is gradually falling, becomes just speculation, but the possibility of thermal runaway is very real, even though the Earth existed at high temperatures without thermal runaway in the past.
Yes, the Earth did encounter 60°C temperatures in the past without thermal runaway, but there was far less solar radiation was arriving at that time, and more CO2, so the conditions were not the same. This will be a new 60°C, with a very different atmosphere, that this time would be at 60°C even without greenhouse gasses and without a thermostat system to prevent thermal runaway.
Thermal runaway is where temperature increases add more water vapour to the atmosphere, starting positive feedback cycle far earlier that raises temperature even further, which in turn result in more water vapour. Since water vapour is a greenhouse gas, more water vapour heats the Earth even more, adding more water vapour as a result. The end result: At some point, Earth will become another Venus with temperatures rapidly soaring beyond those where life is possible.
The question is: “When?”. If there is no thermal runaway effect some of the simplest forms of life could still exist 1 billion years from now, although humans existing as we do now would have become extinct hundreds of millions of years earlier.
As for humans, there are many variables. CO2 has to keep falling over the next 25 million years to even come close to maintaining current temperatures. Most likely temperatures will rise, but slow enough that other have time evolve rather than become extinct. The total amount of life on Earth must continue to decrease, unless humans or some other sentient species can intervene. I do feel we can assume no more than 25 million years before we need to be in a position to intervene, but it is not like one day, 25 million years from now it all ends due to rising temperatures and/or thermal runaway the falling amount of plant life due to further reduced CO2 being unable to provide an atmosphere than matches what humans need. It is gradual, and there is no exact date, so I remain with 25 million years the most we can assume but believe humans could provide solutions much earlier.
Given the rapid pace of technological advancement, 25 million years should be more than enough time to find a solution, but in geological time 25 million years is not that long at all. All things considered for life on the planet; humans only just managed to evolve in time!
Timeline Data.
| Years Relative to Now | date | Time | Source | ||
| Sun Formed | -4,600,000,000 | 1st January | Discover Magazine | ||
| Earth Formed | -4,500,000,000 | 4th January | Discover Magazine | ||
| First Life | -4,000,000,000 | 23rd January | Livescience | ||
| Cyanobacteria | -2,700,000,000 | 13th March | Scientific American | ||
| o2 – Oxygen | -2,400,000,000 | 24th March | Great Oxygen Event | ||
| Eukaryotic (modern) cells | -2,000,000,000 | 8th April | New Scientist | ||
| Algae | -1,200,000,000 | 9th May | Scientific American | ||
| First Animals | -800,000,000 | 24th May | Natural History | ||
| Phanerozoic era begins | -540,000,000 | 3rd June | Phanerozoic era | ||
| Plant Life On Land | -470,000,000 | 6th June | New Scientist | ||
| First Insects | -406,000,000 | 8th June | AAAS.org | ||
| First Dinosaurs | -231,000,000 | 15th June | BBC Science Focus | ||
| First Mammals | -160,000,000 | 17th June | Livescience | ||
| Chicxulub Asteroid | -66,000,000 | 21st June | 09:17 | Chicxulub crater | |
| Humans | -500,000 | 23rd June | 21:03 | Discover Magazine | |
| Civilization | -10,000 | 23rd June | 21:29 | ||
| now | 0 | 23rd June | 21:30 | ||
| Thermal runaway | 25,000,000 | 24th June | 20:19 | ||
| Sun Is A Red Giant | 5,000,000,000 | 31st December |
Updates.
- 2022 October 27: Update more links to the paper ‘future biosphere extinctions‘ and added the possible fossil fuel driven extinction event.
- 2021 May 11: First release.