Last Universal Common Ancestor (I Reincarnated into the Least Universal Common Ancestor and Now I Have to Prepare for the Late Heavy Bombardment?!)

[dhasenan]

New research in Nature: "We estimate the date of the LUCA at approximately 4.2 billion years ago."

A discussion of its characteristics, also in Nature.

A more readable description of the research.

The last common universal ancestor (LUCA) is the most recent organism from which everything currently alive descended from. This research identifies about 2500 likely genes that this organism included, which gives us a pretty good picture of what it was like:

• It was probably a prokaryote instead of something more primitive.
• It had an acetate-based metabolism, consuming hydrogen for energy.
• It probably used organic compounds from other life forms.
• It may have been able to turn into a spore to handle temporary environmental problems.
• It probably produced carbon dioxide and methane as waste products.
• It probably lived in deep sea vents or on the ocean's surface. It has some adaptations to protect against UV damage, but those are also seen in organisms that don't get any significant UV radiation. Deep sea vents aren't a renewable source of hydrogen, though, so if that was its native environment, I'm guessing it had to spread throughout the ocean in spore form to find new vents periodically. If it lived near / on the ocean's surface, waste methane would have broken down thanks to solar radiation to provide more hydrogen, forming a stable cycle.
• It had to deal with viruses and had some protections from them.
• It probably was carbon-fixing, taking in more carbon from the environment (carbon dioxide dissolved in water) than it released.

The 4.2 billion years ago figure is especially relevant if the Late Heavy Bombardment happened, since it would indicate that life can survive and diversify even through repeated high-energy impacts. It's also half a billion years earlier than previous estimates of the emergence of life based on radioisotopes.

 

[Somebody]

How did they figure out the timing for the LUCA?

Prokaryotes can mutate pretty fast due to how often they divide, and then we have horizontal gene transfer. This is very different from eukaryotes, to say nothing of multicellular organisms.

The bigger issue is, their timing for the LUCA suggests that abiogenesis, and the appearance (or is it serendipitous self-assembly) of prokaryotes occurred within 300 to 400 million years after the Earth was formed. Which has massive delays along the lines of "the planet needs to cool down enough for water to condense and fall down as rain".

 

[dhasenan]

How did they figure out the timing for the LUCA?

Prokaryotes can mutate pretty fast due to how often they divide, and then we have horizontal gene transfer. This is very different from eukaryotes, to say nothing of multicellular organisms.

Click to shrink...

They say (and apparently the editors of Nature find it reasonably plausible) that genetic mutation rates with respect to time are pretty consistent. Since they're only comparing within bacteria and archaeans, this is significantly more plausible than if they were comparing mammals and archaeans.