Meet LUCA, the 4.2 billion-year-old cell that's the ancestor of all life on Earth today

Everything alive today descends from a cell that lived 4.2 billion years ago, just a few hundred million years after Earth formed, new research suggests.

That last universal common ancestor, which biologists affectionately nicknamed LUCA, wasn't so different from fairly complex bacteria alive today — and it lived in an ecosystem teeming with other species of life and viruses.

"What is really interesting is that it's clear it possessed an early immune system, showing that even by 4.2 billion years ago, our ancestor was engaging in an arms race with viruses," Davide Pisani, a genomics researcher at the University of Bristol in the U.K. and co-author of the new study, said in a statement.

All cellular life on Earth shares certain key features: It uses the same protein building blocks, everything uses the same energy currency to power its cells (ATP), and all cells use DNA to store information. These commonalities are unlikely to be a coincidence; they all point to the life we know today coming from a single origin.

Related: What is the tree of life?

Prior to this study, scientists estimated that LUCA lived 3.9 billion years ago. However, accurately dating genetic events that occurred so long ago is challenging.

In the new study, published July 12 in the journal Nature Ecology & Evolution, researchers aimed to pinpoint LUCA's origins more precisely. The team compared all the genes in 700 living species of bacteria and archaea (microbes that are similar to bacteria and often live in extreme environments). They chose organisms in these domains because they are thought to be the oldest life-forms, with eukaryotes evolving from a union between both cell types. Then, the researchers counted the mutations that have occurred over time across the genomes and within 57 genes shared by all 700 organisms, using estimated mutation rates to back-calculate when LUCA lived.