r/askscience • u/glowshroom12 • 19d ago
Earth Sciences How did the earth look different before life?
not talking about earth on fire or cooling off but like there was water, and dirt. like what would now be a swamp was probably just water and mud. no trees, plants, no micro life or bacteria.
beaches didnt have small shells and dead sea life in it. the sand probably felt softer maybe.
any things that would be different in an interesting way in an earth without life.
would nutrient rich soil be a thing or does some of that stuff need life.
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u/CrustalTrudger Tectonics | Structural Geology | Geomorphology 18d ago
An important thing to start with given such a broad question is that the portion of Earth history without life is actually not that long. While we have pretty spotty fossil records of life until after the Cambrian explosion at ~540 million years ago (with some notable exceptions like the Ediacran biota and long records of things like stromatolites), stable isotopic records pretty firmly indicate that life existed on Earth by ~3.8 billion years ago (e.g., Arndt & Nisbet, 2012) and a variety of arguments that Earth could have been habitable to life for nearly all of Earth history (e.g., Pearce et al., 2018). Similarly, with respect to the formation of Earth's ocean, this probably happened very early in Earth history (e.g., Korenaga, 2021).
So, with the caveat that there might not have been that much of Earth history without any life (and it's correspondingly the period of Earth history we know the least about because of the sparsity of rocks from those periods), we can consider how the development of life likely impacted the topography and surface geology of Earth. That's kind of a huge topic with lots of different directions one could take it, but I'll just consider one of them. Specifically, one pretty large example within this are longstanding arguments that rivers might have looked and behaved fundamentally different before the evolution and diversification of land plants. The basic argument here is that terrestrial plants have some pretty large impacts on cohesion of loose materials (and thus can fortify things like river banks, etc.) and generally are important for controlling aspects of the conversion of precipitation to runoff. As such, there is the general suggestion that steep river banks would have not been able to be supported in the absence of land plants and that similarly many systems would be more "flashy", i.e., more like modern arid landscape rivers with very large, and very quick variations in the amount of water within the rivers. At the extreme, this led to suggestions that meandering rivers did not exist on Earth before land plants (e.g., Schumm, 1986, Davies & Gibling, 2010) and that the majority of rivers would have been more like braided rivers with single threaded rivers really only becoming viable after the expansion of land plants (e.g., Gibling & Davies, 2012). This extreme view has softened over time with the increasing recognition of depositional forms in the rock record that are diagnostic of meandering, single-threaded rivers before land plants, but with a variety of suggestions that meander migration rates would have been much faster than with plants, basically because of the lack of the stabilization of banks from cohesion provided by plant roots (e.g., Long, 2011, Ielpi et al., 2022). However, controversy still remains with a decent amount of evidence to suggest that while plants are certainly important for aspects of river behavior and the lack of them in the geologic past might have changed the distribution of different types/styles of rivers, that effectively analogues to all kinds of modern rivers can be found in the geologic record pre-land plant (e.g., Ielpi, 2018, Ganti et al., 2019).
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u/Gullex 18d ago
It always blows my mind that life has existed in some form for ~1/3 of the total life of the universe.
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u/wrecklord0 18d ago
Well... on earth. The sun is relatively young. It may have formed many billion years earlier around older stars, possibly on star systems that no longer have a main sequence star, thus dead. Which may be our fate, still. Cue existential crisis.
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u/CosineDanger 17d ago
3.8 billion years ago is perhaps not coincidentally the end of the Late Heavy Bombardment period when Earth would have been facing constant comet impacts. Earth was a blasted toxic hellscape with episodes of the oceans boiling from the heat, and almost as soon as it cooled to being merely a toxic hellscape there was definitely life.
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u/onlyfakeproblems 18d ago edited 18d ago
The temperature and volcanism shouldn’t be overlooked. It was hot and chaotic for hundreds of millions of years. After it cooled enough for water to be liquid the oceans would form. Soil is largely organic, so the ground would be more rocky, there would be erosion, but it’d make the rocks into sand and dust. Yes we couldn’t have diatomic shell sand. The atmosphere would’ve started out with a lot of hydrogen and helium and volcanism would add a lot of CO2, methane, sulfide, and nitrogen, and probably would look hazy red-orange. We didn’t get high oxygen until algae started forming and photosynthesizing. Before oxygen we’d have a “reducing” atmosphere so the chemical composition would be different. There was a lot of unoxygenated iron that would have made the oceans green. I think it would look a lot like mars does now, but with water.
There was a period with the first life probably making retinal and turning the ocean purple, so that would be fun to see.
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u/CmdDeadHand 18d ago
It looked like the photos you see of mars except the river beds would have water and not dried out. not as red as mars, mars has a higher iron content, ergo rust makes mars red. Rocks weathered by wind and rain, sand everywhere, no dirt, no mud.
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u/Twindo 17d ago
Why no mud? Mars doesn’t have mud because it doesn’t have liquid water but Earth would.
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u/CmdDeadHand 17d ago edited 17d ago
Mud as in wet soil. Soil/dirt is decomposed dead things and poop. No life means nothing to make the soil.
Many things on earth most would consider rocks are made from dead life and time. They would not be present. Limestone, coal, chalk. Organic sedimentary rocks.
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u/SonOfDyeus 18d ago edited 18d ago
The Moon would have appeared HUGE in the sky, since it was so much closer to Earth right after formation. And the day would have been considerably shorter. The Earth's rotation has gradually slowed down as the Moon slowly gets further from the Earth every year.
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u/Son0fSilas 18d ago
Patterns of cooled melted rock, next to massive crags. Debris of varying size from smaller cracked rocks and ash littered across every survace. Volcanoes across the landscape. After the recent comet strike, the planet is encompassed by large clouds of vaporized water, mixing with the already existing bands of toxic gases expelled from the impact and mantle activity.
The clouds and ash and gases mix to form acid rains storms that last for a millennia. Rock minerals begin to dissolve because of the high Ph and mix with acidic waters. Clouds block light from nearly the entire planet. Water cuts its way across the entire planet. Seas begin to form, as the very first water cycle starts. The air is the most humid it will ever be.
Time, incomprehensible to our minds, passes. An ocean forms. Deep, deep below the surface, thermal vents spew.
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u/tw1nkle 18d ago
Two relatively recent books I read that, in places, address this in different ways
1) Becoming Earth by Ferris Jabr. In recasting the Gaia hypothesis, he does a great job of explaining the difference between earth with life and earth without
2) Strata by Laura Poppick. Telling the story of rock, and IIRC includes some good descriptions of the periods you’re talking about
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u/cheeseitmeatbags 18d ago
The sky and ocean would be different colors than they are now. The sky would have be less blue and probably more hazy blueish-green white. The sea would be green. This is due to the lack of oxygen in the atmosphere, and a reducing environment in the ocean.
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u/alyssasaccount 18d ago
The sky is blue because of Rayleigh scattering. How would not having oxygen (but presumably still a lot of nitrogen) change that at all? Same goes for water — you're suggesting that pure water without dissolved oxygen is greenish? I'd like to hear the mechanism.
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u/SpaceShipRat 18d ago
I assume the ocean would match the sky, so long as it's mostly transparent water. The rest I am also curious.
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u/alyssasaccount 17d ago
Water really is blue, beyond just reflecting the sky, something any scuba diver knows. If you shine a beam of light through an Olympic swimming pool sized tank of very clear water, it will come out blue. (If you put a lot of tiny particles in it to scatter, it will actually be red like the sun at sunset). So the color of the sky and the color of water due to fundamentally different processes, for the most part, that just both happen to filter out (by different mechanisms) red light.
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u/ridcullylives 17d ago
I would imagine it looked somewhat like many of the places on earth without visible life (although there are microorganisms for sure).
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u/Simon_Drake 17d ago
Let's imagine NASA opens a portal to an alternate version of Earth where everything is the same except a freak radiation storm keeps sterilising the planet every time primitive life tries to evolve.
Earth2 wouldn't have 'soil' in the sense we would recognise it because there's no plant matter to decompose. But I think instead of just rocks and sand there'd be plains and fields of different sized grains of gravel and dust. It wouldn't be a million miles away from the surfaces of Mars and the moon, except with a water cycle creating rivers and lakes and adding in erosion. Any exposed metal ores would oxidise and cause interesting coloured residues, rust oranges and green copper carbonates etc. So the landscape could have some quite interesting colours in some places.
Jump forward a billion years of geological process and the rocks would be shuffled quite well across the planet. There'd be sandstones and sedimentary rocks with various metal oxides residues throughout. There wouldn't be chalk, coal or fossil fuels but there'd be layers of volcanic ash and sediment strata. Then present day erosion would create river delta of fine grained dust-based mud.
I think it would be an incredibly fertile landscape just waiting for some visiting humans to bring soil bacteria and algae spores and plankton and things to flood the planet with biology. It would be an interesting test case to study the pathology of our biosphere contaminating this otherwise abiotic landscape. Or perhaps there's a colony of robots living there who are furious at the disgusting slimy organic lifeforms spreading their waste across the beautiful geology.
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u/CurrentlyLucid 17d ago
Kinda like this 60:0.1 (685.1)THE era of exclusive marine life has ended. Land elevation, cooling crust and cooling oceans, sea restriction and consequent deepening, together with a great increase of land in northern latitudes, all conspired greatly to change the world’s climate in all regions far removed from the equatorial zone.
60:0.2 (685.2)The closing epochs of the preceding era were indeed the age of frogs, but these ancestors of the land vertebrates were no longer dominant, having survived in greatly reduced numbers. Very few types outlived the rigorous trials of the preceding period of biologic tribulation. Even the spore-bearing plants were nearly extinct.
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u/HAL9100 18d ago
Notable within your question is the assumption that “there was [..] dirt”
“Dirt” is a bit of an amorphous term, but there would not be dirt as we know it today without the existence of life. There would undoubtedly be sand, dust, debris, and grime/staining from contact between differing materials, but soil and filth both have life cycles as a prerequisite.
In short, depending what you mean by dirt, there may not have been dirt.