John Carlos BaezWho are we all descended from? And I mean πππ - people, birds, plants, bacteria, archaea....
It's called ππ¨ππ: the last universal common ancestor. And people have been trying to track it down. By comparing the genomes of different organisms you can infer a tree of life and guess where it leads back to.
This new paper suggests that LUCA lived about 4.2 billion years ago, with a genome having about 2.5 million base pairs.
They guess it was a prokaryote: a single-celled organism with no nucleus. They guess it was anaerobic. Neither of those are at all surprising. More interestingly, they guess it was an acetogen! I hope you know acetic acid is what makes vinegar sour. Nowadays, 'acetogens' are bacteria that power themselves by converting carbon dioxide and hydrogen to acetic acid and water:
2 COβ + 4 Hβ β CHβCOOH + 2 HβO
This produces less energy than fermentation, which converts glucose to acetic acid. But hey: sometimes there ain't no glucose around.
The paper says that the metabolism of LUCA could have provided a niche for other microbes living at the time, and recycled hydrogen they made. It's the blue box in the web of chemical reactions carried out by early organisms in the picture at left.
At right you see how if bacteria called methanogens were also also around, they could put methane (CHβ) into the atmosphere, which gets broken down to Hβ by sunlight. When this dissolved in water, acetogens can eat it!
The paper is open access:
β’ The nature of the last universal common ancestor and its impact on the early Earth system, https://www.nature.com/articles/s41559-024-02461-1
The nature of the last universal common ancestor and its impact on the early Earth system - Nature Ecology & Evolution
Integration of phylogenetics, comparative genomics and palaeobiological approaches suggests that the last universal common ancestor lived about 4.2 billion years ago and was a complex prokaryote-grade anaerobic acetogen that was part of an ecosystem.
Bartosz Milewski