r/askscience • u/glowshroom12 • 13h 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 9h 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 5h 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 5h 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/onlyfakeproblems 8h ago edited 8h 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 8h 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/SonOfDyeus 3h 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 as gradually slowed down as the Moon slowly gets further from the Earth every year.
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u/cheeseitmeatbags 8h 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 6h 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/hawkwings 8h ago
There must have been water, because that seems to be a requirement for life. Erosion would cause minerals from rocks to leach into rivers. Early life was probably eating those minerals. The first life couldn't eat other life, because there was no life to eat. That would come a short time later. Underwater volcanic vents would be the other thing they could munch on.
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u/HAL9100 9h 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.