If life never emerged on Earth, would the continents still be more or less the same today? In other words, does life affect the formation and movement of continents significantly?
I'm not sure how much of a difference that would make. That's less than the total cumulative CO2 emissions of China and the US, and it's 1% of 1% of the total mass of the atmosphere
That’s a good point. My number is all of the current biomass (according to Wikipedia), but all the CO2 we’ve produced since the Industrial Revolution was also originally captured by living things. So add all the gas and coal that ever existed on earth to that number.
So a few things that are missing from the current answers. I’m not a geologist, but I have had graduate level paleobotany training, and quite a bit geology coursework. I also worked in paleobotany lab. I do currently do research in biogeochemical cycling, so while I can’t speak to the nature of continent or mountain building, but I can speak to how our planet has changed chemically, and that in many ways, life on earth has already fundamentally altered major components of the biogeochemical processes that result in geologic formations. This is not quite what you asked, but I think a geologist with the right training could weigh in on the back to further the conversation.
So the two processes I would speak to are the formation of bituminous coal , and the formation of limestone, both of which are biological in origin.
Coal as a type of sedimentary rock involves the conversion of dead vegetation in wetlands, when vegetation dies and is submerged in an anoxygenic environment. The basic process is that vegetation grows, dies, and is buried in a low oxygen environment, and eventually turns into coal, which has retained most of the C-C bonds that were originally present in the plant tissue (cellulose). So how important is evolution and life to the formation of coal? Well consider that 90% of coal beds were deposited during the Carboniferous and Permian periods, representing only a brief fractions of earths geological history. Why would this be the case? Well, it was during the Carboniferous that plants evolved lignin, a plant molecule that is not only very resilient to decomposition, but is a structural tissue that allows for the building of large, indeterminate plant parts. This resulted in the first “trees”, which is to say, tall woody plants that could extend a significant distance above the ground because they now had a strong reinforcement polymer they could integrate with cellulose. So all of a sudden, plant life was like “Fuck yeah, trees upgrade unlocked”!
HOWEVER fungi and bacteria had not yet evolved to degrade lignin. Which meant, for around 160 million years, trees were going gangbusters, but no organism had yet evolved to significantly decompose lignin; this resulted in the wood just kind of piling up, and where you had wetland conditions suitable for coal formation, you got coal. So for around 2% of earths history, we had trees, but we didn’t have wood-decomposing fungi. There are other factors at play here like the high oxygen levels from all the plants, and extremely high CO2 levels from ongoing volcanism (I believe the Kamchatka volcanics?), but if not for the evolution of lignin, we would not have coal, and if not for the evolution of wood-decomposing fungus, the formation of coal would not have been curtailed significantly.
I know much less about the formation of limestone, except that there a shit ton more of it than there is coal, but I can speak to it enough to make a few points. Limestone forms mostly in shallow marine environments. Limestone is made from coral and forminfera, basically shell bearing microorganisms. Anything with a shell that lives and then eventually dies in a marine environment can lead to the formation of limestone. Limestone makes up around 25% of the sedimentary rocks on planet earth, which is a shit ton of shells. Its been forming for a very long time.
So a few more considerations. Consider that sedimentary rocks like coal or limestone are much lighter than igneous rocks. Continental crust is like rafts of light rock floating in a sea of heavier oceanic crust. So there is a kind of geological selection process for these lighter rocks to accumulate as continental crust rather than be subducted and then stay subducted. I’m going to stop there because that’s too deep into the geology for me to speculate further on. I can speak to the biogeochemical aspects, but I’m not a geologist.
So from a chemical perspective, the contents of the minerals that make up continental crust have ABSOLUTELY been altered by the trajectory of evolution on planet earth. Now if that would fundamentally alter the outlines of the continents or their movements? That’s beyond what I know about earth history. What I can say is that evolution has had a direct impact on the chemical composition of the atmosphere, and the makeup of major rock and mineral formations that represent a significant portion of the earths crust.
I just want to add all of the organic material that makes soil different from sand. Erosion will turn rocks into small rocks which we call sand. It's plants, fungus and animals that make that into soil. They all work together to digest and excrete what makes up soil. Not to mention that it's fungi that dissolve minerals to make them bioavailable to everything else. So there's lots of ways life changed the surface but I don't know about the base continents
Adding all of that coal and limestone trapped a lot of carbon underground. If that carbon was CO2 instead, the Earth would be much hotter. Perhaps hotter than the boiling point of water and thus there would be no ocean between the continents, like Venus.
The atmosphere sure changed a lot because of life, which might have had its effects on incoming solar radiation? Which might have changed the temperatures of some ocean currents/continental plates? I don’t think it would differ significantly
I think pretty much everything on land would be different: plant induced precipitation, river bank stabilization, carbon sequestration changing the climate and the timing/duration of ice ages and hydrocarbons being ignited by flood volcanism events. All of that would be gone, could even rearrange whole mountain ranges over time by by altering the pressure of glaciers ice on tectonic plates.
I’m no earth doctor, but wouldn’t it be the other way around? Continental drift would affect the lifeforms abilities to survive and adapt, and that in turn would affect the continents surface features, but not the drifting itself?
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