Now we have the best picture yet of what that ancestor was like and where it lived, thanks to a study that identified 355 genes that it probably possessed.
LUCA emerged around 3.8 billion years ago and gave rise to two kinds of simple cells: bacteria and archaea (see diagram, below). By looking for genes common to almost all cells living today, previous studies have identified around 100 genes almost certainly present in LUCA.
The 355 they found include some universal genes, such as a few involved in reading the genetic code. But others point to a very distinctive lifestyle.
One characteristic of almost all living cells is that they pump ions across a membrane to generate an electrochemical gradient, then use that gradient to make the energy-rich molecule ATP. Martin’s results suggest LUCA could not generate such a gradient, but could harness an existing one to make ATP.
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