Luca, acronym of “Last Universal Common Ancetor” (last universal common ancestor), is considered by scientists as the ancestor common to all forms of life on earth. Recent research reveals that Luca would have lived around 4.2 billion years ago, at a time when our planet was still young and hostile.
A complex ancestor in a primitive world
According to a study published in July 2024 in the journal Nature Ecology and Evolution and highlighted by The Guardian, an international team of scientists partially reconstructed the genome of Luca. Unlike the previous hypotheses which described it as a simple organism, Luca had a genome coding for around 2,600 proteins, indicating a surprising complexity for such a distant era. This complexity suggests that life on earth emerged and evolved quickly after the formation of the planet.
During this period, the earth, often described as Hadéenne in reference to Hades, the Greek god of hell, was characterized by intense volcanic activity and frequent impacts of meteorites. The atmosphere was rich in carbon dioxide, probably giving the sky a less blue, even orange shade due to a possible mist of methane. The planet was mainly covered with oceans, with only a few volcanic islands emerging on the surface. The days lasted approximately 12 hours due to a faster terrestrial rotation, and the proximity of the Moon would generate stronger tides than today.
An extraterrestrial life possible
The discovery of the complexity of Luca and its early appearance on Earth suggests that life could emerge quickly when the conditions are favorable. This hypothesis questions the idea that life is a rare and improbable event. If life has been able to appear quickly on earth, it is plausible that it can also emerge on other planets with similar conditions, such as Mars or Venus in their distant past.
-In addition, the presence of a rudimentary immune system in Luca, similar to the CRISPR-CAS system of modern bacteria, indicates that viruses already existed at that time. These viruses could have played a crucial role in the horizontal transfer of genes, promoting rapid diversification of life. Thus, the tree of primitive life could more like a complex network of organisms exchanging genetic equipment, rather than a simple tree structure.
These discoveries reinforce the idea that life, once established, can influence its planetary environment to maintain habitable conditions, a concept known as the Gaïa hypothesis. This suggests that similar biospheres could exist elsewhere in the universe, waiting to be discovered.
