Enter LUCA, a 4.2 billion-year-old cell that is the ancestor of all life on Earth today.

New research suggests that everything alive today is the descendant of a cell that lived 4.2 billion years ago, just a few hundred million years after the Earth was formed. This last universal common ancestor, which biologists affectionately called “LUCA,” was not so different from the fairly complex bacteria that live today, living in an ecosystem full of other life forms and viruses. “What’s really interesting is that it clearly had an early immune system, which shows that our ancestors were already in an arms race with viruses 4.2 billion years ago,” says Davide Pisani, a genome researcher at the University of Bristol in the US.

The Kingdom authors of the new study said in a statement. All cellular organisms on Earth share certain key characteristics. They use the same protein building blocks, all cells use the same energy source (ATP) to power their cells, and all cells store information in DNA. These similarities are probably not coincidental. They all suggest a single origin for life as we know it today. A new study suggests that everything alive today is the descendant of cells that lived 4.2 billion years ago, just a few hundred million years after the Earth formed. This last universal common ancestor, which biologists affectionately called “LUCA,” was not so different from the fairly complex bacteria that live today, living in an ecosystem full of other life forms and viruses.

“What’s really interesting is that it clearly had an early immune system, which shows that our ancestors were already in an arms race with viruses 4.2 billion years ago,” said Davide Pisani, a genome researcher at the University of Bristol in the UK, and co-author of the new study, in a statement. All cellular life on Earth shares certain key characteristics: they use the same protein building blocks, all cells use the same energy currency to power their cells (ATP), and all cells use DNA to store information.

These similarities are probably not coincidental; they all point to a single origin for life as we know it today. Prior to this study, scientists estimated that LUCA lived 3.9 billion years ago. However, it is difficult to precisely date genetic events that occurred so long ago. In a new study published in the journal Nature Ecology & Evolution, the researchers wanted to pinpoint LUCA’s origins more precisely. The team compared the entire genes of 700 species of extant bacteria and archaea (microbes that are similar to bacteria and often live in extreme environments).

They chose organisms from these domains because they are thought to be the oldest forms of life, and eukaryotes arose from a combination of both cell types. The researchers then counted the mutations that occurred over time across the entire genome, and in 57 genes common to all 700 organisms. Using the estimated mutation rates, they calculated how long LUCA might have lived.