Last universal common ancestor

The last universal common ancestor (LUCA), also called the last universal ancestor (LUA), cenancestor, or (incorrectly) progenote, is the most recent population of organisms from which all organisms now living on Earth have a common descent - wikipedia

Charles Darwin proposed the theory of universal common descent through an evolutionary process in his book On the Origin of Species in 1859, saying,

Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.

This is a image of the more or less current tree of life showing the 5 kingdoms and how genetic inheritance is now thought to be not exactly vertical but also includes horizontal gene inheritance via at least virus infection and maybe other routes such as the incorporation of mitochondria and plastids as symbiotic partners within Eukaryote cells. - wikimedia.org

LUCA is the most recent common ancestor of all current life on Earth. LUCA should not be assumed to be the first living organism on Earth.

The LUCA is estimated to have lived some 3.5 to 3.8 billion years ago (sometime in the Paleoarchean era).

The composition of the LUCA is not directly accessible as a fossil, but can be studied by comparing the genomes of its descendants, organisms living today.

The LUCA used the Wood–Ljungdahl or reductive acetyl–CoA pathway to fix carbon - wikimedia.org

By this means, a 2016 study identified a set of 355 genes inferred to have been present in the LUCA. This would imply it was already a complex life form with many co-adapted features including transcription and translation mechanisms to convert information between DNA, RNA, and proteins.

Some of those genes, however, could have been acquired later by horizontal gene transfer between archaea and bacteria.

The earliest evidence of life on Earth is biogenic graphite found in 3.7 billion-year-old metamorphized sedimentary rocks discovered in Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.

A 2015 study found potentially biogenic carbon from 4.1 billion years ago in ancient rocks in Western Australia, but such findings would indicate the existence of different conditions on Earth during that period from those generally assumed today, and point to an earlier origin of life.

In 2017, there was a published description of putative fossilized microorganisms that are at least 3.77 billion, and possibly 4.28 billion years old, in ferruginous sedimentary rocks in Quebec, Canada.