I have more thoughts and additional information!
(actually I've had these more thoughts since like the day after my first reblog, but I'm finally getting around to posting them!)
most of this comes from Wikipedia, btw. I've provided links :)
okay Thought The First. if LUCA was alive during the Hadean, the organisms that retained the most similarities are probably, like, the deep volcanic vent microbes. anaerobic little beasties living on sulphuric acid or some shit. LUCA lives on Mustafar, pass it on.
Thought The Second. we are talking about the planet where one kind of organism produced a TOXIC GAS and suddenly ended up poisoning like, 99% of the rest of life on the planet, and now the Earth is TEEMING with life again and 99% of that life depends on that toxic gas.
because that toxic gas is oxygen. we live in a post-apocalyptic setting where the atmosphere became deadly and killed the majority of organisms at the time of the apocalypse! and it permanently changed life on this planet because we all just got used to the horribly toxic gas and now we can't live without it. we have gone through several more mass extinction events and we're still all toxic-gas-breathers. insane.
in fact it changed more than that, because prior to the Great Oxygen Catastrophe (yes, people really call it that), we had no chlorophyll. like... chlorophyll is kind of what kickstarted oxygen production and created the Great Oxygen Catastrophe. so before chlorophyll, organisms had a different molecule that generated energy from sunlight. that molecule is anaerobic and thus isn't super great in an oxygen-saturated environment like, well, most of Earth's surface. (it's pink, there's a very cool artist's rendition you can see here.) but don't worry, we actually still use it! it's called retinal and we use it to see instead of to breathe. :)
(also, btw, the Great Oxygen Catastrophe actually is not included in the list of mass extinction events, because nothing prior to the Cambrian Explosion is really included in known mass extinction events, because we don't have enough fossil evidence to say how much life perished. so that's neat. there's probably many more mass extinction events that we just don't count because we don't have enough evidence to know they happened.)
Thought The Third. NOW FOR THE EXTRA FUCKED UP STUFF. we really are a Lifeworld, guys! :D
because there is something called the ~*~deep biosphere~*~
it is exactly what you think it is! a biosphere that is very deep! it reaches from a few meters below the surface (both continental and sea floor) to a depth between 6 and 12 miles. temperatures go from "normal" ground temperature (in the 50s Fahrenheit) to ~250 Fahrenheit (120 Celsius). why yes that is above water's boiling point at sea level! not here in the deep biosphere, though. the pressure from the miles of Earth's crust above it means water boils at 400 Celsius instead of 100. :)
and yes, there's life down there. :) all three domains, in fact! Bacteria, Archaea, and even Eukarya, complex cells with nuclei. :)
about 90% of the biomass of Bacteria and Archaea is in the deep biosphere. please pause and consider just how many bacteria are here, on the surface, on a single human. please recall some scientists estimate that we are more bacteria/virus/etc by weight than human cells. now consider how much more are in 12 miles of crust of the entire Earth that the deep biosphere contains 90% of their biomass.
but wait, there's more! I said the domain Eukarya is represented down there, right? complex cells? complex life?
there's fungi down there, miles beneath the surface. there's fucking animals down there, invertebrates, mostly worms and arthropods.
there are aerobic organisms down there. microbes that split nitrates into nitrogen and oxygen, then use the oxygen to metabolize methane. some of that oxygen leaks into the environment for other organisms.
speaking of methane! in fact, the deep biosphere serves a very important function! about 90% of methane is metabolized as an energy source before it reaches the surface; it can be produced by biological processes but also by chemical processes deep in the mantle (where there really isn't any life). this is a very important cap on greenhouse gas emissions that are not human-derived. we'd probably be much hotter without miles of microbes eating methane. :)
so yes, literally nowhere on Earth is free of life. you have to get down nearly to the literal molten rock to find a place life cannot survive. (I am exaggerating, but not much - the deep biosphere's lower limit ranges from 5km beneath continents to 10.5km beneath the ocean. the upper mantle's upper margin ranges from 7 to 35 km beneath the surface.)
15% of biomass is in the deep biosphere. 15%!!! when all the plants and big animals are up here, on the surface! that's insane! this planet is insane. I love it here.
