Update on LUCA and the origin of life on Earth

August 04, 2024

LUCA is the Last Universal Common Ancestor of all life on Earth. Recent research indicates that this bacteria-like single celled organism arose roughly 100 million years after conditions of Earth could support life, about 4.2 billion years ago. Not all scientists believe this was possible because the Earth was possibly under heavy bombardment. The Late Heavy Bombardment (LHB), also known as the lunar cataclysm, is a theory that a large number of asteroids and comets collided with Earth and other inner solar system planets between 4.1 and 3.8 billion years ago. The bombardment may have lasted 20–200 million years. LUCA arose within that time frame, assuming there was such a thing as the LHB.

What is baffling to me is that researchers think it is possible that LUCA had am immune system to fight off viruses. In my opinion, there had to be something earlier that had no immune defenses because viruses do not arise from nothing. This strikes me as a strange thing to hypothesize, maybe unless LUCA evolved cells that could fossilize when viruses already existed.

Those spider-like things on the cells are modern

complex viruses that attack modern bacteria

A WaPo article discusses the research:

It may be hard to imagine complicated life forms on early Earth. Oxygen was low and asteroids may have been pelting the baby planet’s surface. Despite those harsh conditions, a microbe may have persisted, giving rise to all life we see today.

This is the Last Universal Common Ancestor, or LUCA.

In the most extensive analysis of the organism to date, scientists propose in a new study that this hypothesized ancestor was more sophisticated than previously known — thought to possess an immune system to fight off viruses, for instance.

The team said LUCA appeared around 4.2 billion years ago, shortly after Earth was thought to be habitable, suggesting it evolved even quicker than previous estimates and survived through tumultuous times on the planet. .... The organism would possess genes and components present in all living forms today, such as ribosomes, certain proteins or enzymes important for energy.

Our late ancestor might not have been alone either, [researcher and lead author] Edmund Moody said. Although not a direct conclusion from the study, he suggested LUCA probably would have been part of an early ecosystem of many organisms, competing to stay alive. But the other organisms probably died out, which would explain why they wouldn’t be represented in any modern genomes or fossils.

“LUCA was a very complex cell, with a genome similar to modern bacteria (which we think of as simple, but from a molecular biology perspective are very complex),” Aaron Goldman, a biologist at Oberlin College who was not involved in the study, said in an email. He called the study a “breakthrough in the discipline” in a review article of the study.

Although Earth was formed nearly 4.6 billion years ago, scientists think our planet wasn’t cool enough for habitable environments until about 4.3 to 4.4 billion years ago, said Goldman. If LUCA was indeed around 4.2 billion years ago, as the study suggests, this dating would rewrite our understanding of how fast life can emerge under the right conditions.