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What if all life (plants, animals, bacteria, fungi, and everything from the smallest cell to the largest whale) disappeared instantly?

And here I don't mean things related to the disappearance of humans such as the erosion of buildings and the fall of satellites, but I mean something related to climate change due to the disappearance of plants and bacteria and things like that within tens of millions of years

question here: What will the Earth look like after 50 million years of the disappearance of all life?

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    $\begingroup$ Does the biomass disappear, or does everything die instantly? $\endgroup$
    – outis
    Nov 19, 2021 at 20:56
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    $\begingroup$ Also, if it was "just everything died instantly", how deeply did it go? Did aminoacids remain? How about proteins? Nucleic acids? DNA? Viruses? I.e. if enough building blocks of life remained (but nothing "alive"), and environment remained habitable, it is quite possible life would spontaneously reappear during that timeframe. Or did something (for example) removed all water from Earth causing death in that way? Or so highly irradiated everything that most non-trivial chemical bonds broke? The results vary heavily on that state... $\endgroup$
    – Matija Nalis
    Nov 19, 2021 at 21:54

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Without lifeforms continuously cracking oxygen from gaseous oxides (mainly CO2, and Sulfur and Nitrogen Oxides) the atmosphere would revert to something like it's preoxygenation composition as much, all?, of the carbon currently in long-term sinks like peat and coal will be oxidised. The exception is probably methane, there will be little to none because there will be no methanogens producing it and it oxidises to CO2 and water relatively quickly. The atmosphere is going be high in greenhouse gases and will warm rapidly, and continuously. After 50MA Earth will be a wetter, lower pressure, version of Venus, the atmosphere will be actively acidic and there will be higher surface pressure due to high levels of water vapour and the liberation of gas forming elements from biogenic minerals and existing organic deposits. The high levels of sulfur and nitrogen oxides in the atmosphere will give it a brown/yellow haze/smog.

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It would look like a barren planet, something along Mars, with just a thicker atmosphere and maybe more water.

Though all life is gone, so there is no biological agent to decompose organic matter, geology is still active: sediment deposition will cover and hide any biological trace, and what will remain will be rock in different stages of weathering.

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Basically what you can see in most of our current dry deserts. With at most ice/snow where it falls.

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    $\begingroup$ Also, on this time scale most if not all of the free oxygen would be gone, so I guess the atmosphere would be almost entirely nitrogen. $\endgroup$
    – ShellGhost
    Nov 19, 2021 at 11:23
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    $\begingroup$ @LDutch you show a desert world.. All traces of life ended up in the sediment. But when sediments exist, there are rivers. Large lakes could persist for millions of years, and fjords.. I actually doubt if the idea underlying this question is plausible. Without magic, life will not completely disappear. As long as there is any fluid water left on the planet, species will adjust to live there. $\endgroup$
    – Goodies
    Nov 19, 2021 at 11:38
  • $\begingroup$ Dead soil turns red in the presence of O2, then w/o O2: no change, then gray provided there's microbes (which there aren't) and finally, "rotten egg color".... Red like Mars, +1. soils4teachers.org/files/s4t/color-changes.pdf $\endgroup$
    – Mazura
    Nov 20, 2021 at 1:10
  • $\begingroup$ O2 will quickly be converted to co2 by the oxidization of biological remains. without life the atmosphere will be nitrogen and co2 just like the early earth. $\endgroup$
    – John
    Nov 20, 2021 at 3:09
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If we're talking specifically about what the planet would look like, then fields of grass would be reduced to nothing but soil, forests would be reduced to deserts or barren wastelands, and there would be no more coral reefs dotting the ocean floors. As you'd probably expect, anywhere life has once stood is now desolate and empty.

Considering that this is only going to affect biological life, anything manmade or artificial will probably still be standing proud for a while, but after millions of years, erosion would eliminate most of it. Buildings, even the most well-made ones, would surely be reduced to rubble. Only the sturdiest manmade items would survive.

Photosynthesis would come to a complete stop, so there would be no new oxygen made. We have also eliminated life breathing out carbon dioxide, so it seems like the levels of it would be stable. However, volcanoes would most likely be pumping out large amounts of CO2, though, so the balance would undoubtedly be thrown off. Without plants constantly making more oxygen, the air might be near unbreathable after a while, especially after millions of years.

One thing I have not seen mentioned yet is the effect of nuclear power plants or other similar things would have after being abandoned and falling into disrepair. Humans have a lot of toys that they mess with. If they are completely abandoned for thousands of years, even the most well-made ones will break apart and contribute to this wasteland. Artificial materials would erode bit by bit and add a lot of unique features to this land of desolation.

Without life, the world would be a living hell, but, at the same time, if no one's there to witness the destruction, then there's no reason left to care.

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  • $\begingroup$ Soil has living microbes in it- without those it would be mud and sand. $\endgroup$
    – user2617804
    Nov 19, 2021 at 22:25
  • $\begingroup$ That's a good point. $\endgroup$
    – Nyctophobia457
    Nov 19, 2021 at 22:40
  • $\begingroup$ yes the air would be like the earths ancient atmosphere dominated by co2 and methane. but nothing man made is going to survive unless it gets buried and "fossilized" $\endgroup$
    – John
    Nov 20, 2021 at 3:07
  • $\begingroup$ I know that rust and erosion would probably reduce most buildings to rubble, but wouldn't the materials themselves still exist, or would they just be so degraded it hardly counts as manmade anymore? $\endgroup$
    – Nyctophobia457
    Nov 20, 2021 at 3:39

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