The last universal common ancestor (LUCA) was a living cell that existed 4.2 billion years ago, during a time when Earth had hot oceans and very little oxygen.
Researchers have discovered that all living organisms today trace their origins back to a single living cell that existed 4.2 billion years ago, just a few hundred million years after Earth formed, as reported by Live Science on August 24. The last universal common ancestor (LUCA), or more fully, Luca – Last Universal Common Ancestor, is not very different from the relatively complex bacteria we have today. This new study was published in the journal Nature Ecology and Evolution.
All cellular life on Earth today shares a number of key characteristics, such as using the same protein building blocks, utilizing the same energy form to power the cells (ATP), and all cells use DNA to store information. These commonalities are unlikely to be coincidental and suggest that life, as we know it today, originated from a single source.
It is believed that LUCA emerged near deep-sea hydrothermal vents, while some opinions suggest it lived in small ponds. Researchers began studying LUCA by analyzing about 2,000 genes from modern bacteria to understand the evolutionary connections between modern bacteria and LUCA. If a link is found, it could confirm that LUCA is indeed our ancestor, the source of all life on Earth today.
Single-celled organism LUCA.
LUCA is thought to have existed on Earth about 3.8 billion years ago, and it is the origin of the first two simple life forms in the world, which include bacteria and archaea, and eventually could have given rise to plants and animals. However, in this new study, experts aimed to pinpoint the origins of this cell more precisely. They compared all the genes in 700 species of modern bacteria and archaea. Then, they counted the mutations that occurred in the gene pool and in 57 common genes of all 700 organisms, using the estimated mutation rate to calculate when LUCA was alive.
As a result, the research team determined that this cell lived about 4.2 billion years ago. “We didn’t expect LUCA to be so ancient, appearing just a few hundred million years after Earth formed,” said co-author Sandra Álvarez-Carretero, a PhD student at the University of Bristol. At that time, during the Hadean era (4.6 – 4 billion years ago), Earth was inhospitable for life, with hot oceans and very little oxygen in the atmosphere.
By classifying genes based on cellular function, the research team could learn more about what LUCA ate, where it lived, and how it survived. Their analysis did not pinpoint the exact habitat of this cell but suggested that it may have lived in an oceanic environment, possibly at a shallow hydrothermal vent or a hot spring. LUCA may have also been able to withstand extremely high temperatures and “breathe” without oxygen, instead relying on the waste products of other organisms within the same ecosystem.
Simulation of LUCA being attacked by a virus 4.2 billion years ago. (Image: Science Graphic Design).
The new study indicates that LUCA was not alone. Evidence comes from the reconstruction of its metabolic pathways. This process shows that it may have derived energy from organic materials that other microorganisms broke down. Another supporting piece of evidence is that LUCA possessed genes that helped it resist infectious viruses.
The fact that LUCA lived in a thriving ecosystem so long ago holds intriguing implications for life on other planets, according to co-author Philip Donoghue, a paleobiologist at the University of Bristol. “This suggests that life could be flourishing in Earth-like biospheres elsewhere in the universe,” Donoghue stated.
