Nature of the last universal common ancestor
I read a paper: The nature of the last universal common ancestor and its impact on the early earth system
The citation is:
Moody, E.R.R., Álvarez-Carretero, S., Mahendrarajah, T.A. et al. The nature of the last universal common ancestor and its impact on the early Earth system. Nat Ecol Evol 8, 1654–1666 (2024). https://doi.org/10.1038/s41559-024-02461-1
It’s open access, here’s the PDF version.
It’s another attempt to figure out what the Last Universal Common Ancestor (LUCA) of everything alive today looked like. It’s not a bad paper. I did not understand their methods of assigning probabilities to the presence or absence of particular pieces of genome, but the rest of it was clear and interesting.
The authors use genome sequencing data from 350 Bacteria, and 350 Archaea
They came up with an age for LUCA of 4.2 billion years ago, which is pretty old. Lots of other estimates of when LUCA was around are much younger than this because of the Late Heavy Bombardment. The authors of this paper suggest that the Late Heavy Bombardment may not have been very heavy, or even happened at all. This suggestion isn’t all that surprising, there is no single geologic or paleontologic theory that does not have a large opposition faction.
The authors come up with LUCA about as complex as a modern prokaryote organism and a metabolism that produces acetate as waste product. It was a heterotroph, it did not have chlorophyll. The authors have LUCA much more complex than a pregenote organism, using DNA for replication. They give a couple of different places for LUCA to have lived, first in the chemical-laden water near a ocean bottom vent, second on the surface of the early earth’s ocean, settling on the ocean surface as most likely.
This is different than other attempts at reconstructing LUCA, but the authors go further, trying to figure out what the implications of such a common ancestor. They think LUCA’s metabolism means it lived in an ecosystem, with other forms of life that have no descendants today.
There are weird implications to all this, like life evolving very early in earth’s history, and very rapidly. Since LUCA had a DNA genome, LUCA evolved after DNA evolved. LUCA didn’t have some weird RNA-based replication, or a mixed RNA and DNA replication.
For some reason, I’m saddened by the thought of a whole ecosystem of different types of life that have no descendants today. There’s lots of extinct clasess of animals, like trilobites, but in this case, we’re possible talking entire domains or kingdoms of life that no longer exist.