LUCA latest: more details (Introduction)

by David Turell , Wednesday, November 20, 2024, 22:35 (11 hours, 15 minutes ago) @ dhw

The most recent study:

https://www.quantamagazine.org/all-life-on-earth-today-descended-from-a-single-cell-mee...

"In 2024, Moody and a team of interdisciplinary researchers, including geologists, paleontologists, system modelers and phylogeneticists, combined their knowledge to build a probabilistic model that reconstructs modern life’s shared ancestor and estimates when it lived.

"The analysis sketched a surprisingly complex picture of the cell. LUCA lived off hydrogen gas and carbon dioxide, boasted a genome as large as that of some modern bacteria, and already had a rudimentary immune system, according to the study. Its genomic complexity, the authors argue, suggests that LUCA was one of many lineages — the rest now extinct — living about 4.2 billion years ago, a turbulent time relatively early in Earth’s history and long thought too harsh for life to flourish.

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"Not all experts in the field agree, however. Some argue that a few hundred million years is not enough time for complex life to have evolved. The authors stress that their analysis is a first attempt to paint a fuller, admittedly fuzzy, picture of LUCA. “I fully expect and hope people prove us wrong in certain aspects,” said Moody, the paper’s lead author, especially if those new results offer a clearer view of the ancient ancestor of all life we know.

"It’s no small task to puzzle out the nature of an entity that lived so long ago on fragmentary, inferential evidence. Microscopic fossils can get researchers part of the way, but the oldest traces of life date to only around 3.5 billion years ago, likely long after LUCA lived. That leaves LUCA’s descendants for us to study. “The way to study LUCA is to compare the diversity of genes and physiologies and metabolisms today, and then work backward,” said Fournier, who was not involved in the new work.

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"One way to isolate the signal from evolutionary noise is to select only genes and proteins that show little evidence of horizontal gene transfer. The most prominent analysis of this sort, from 2016, suggested that LUCA was a relatively simple entity(opens a new tab) that was only “half alive,” dependent on the geochemistry of hydrothermal vents for energy. However, such a conservative focus on only the most obviously shared genes and proteins could bias researchers, leading to a conception of LUCA that is too simple, Donoghue said.

"So, instead of a binary, in-or-out approach, Moody and his colleagues computed the probability that a given gene was present. By comparing the gene trees to the species trees, the researchers estimated rates of horizontal gene transfer, gene loss and other evolutionary processes that could muck up the picture. At the end of the process, they assigned each gene a probability of having been part of LUCA’s genome.

“'They’ve taken the best-practice approach for a single family and scaled it up,” Goldman said.

"The team identified 399 gene families with a high chance of having been in LUCA, a number roughly in line with the conservative 2016 analysis. By also integrating the probabilities of thousands of other gene families, they estimated that LUCA’s genome likely encoded about 2,600 proteins — making it similar in size to the genomes of some modern-day bacteria.

"Given what’s known about these proteins, “you get a picture of this fairly complex organism,” Moody said. LUCA likely existed without oxygen by converting carbon dioxide and hydrogen gas into energy. Those inputs might have come from nonliving sources, such as hydrothermal vents or atmospheric gases at the ocean’s surface.

"Alternatively, LUCA may have dined on the chemical waste of other creatures, suggesting that it was already part of a complex ecosystem with other microbes. The analysis can’t provide direct evidence of this possible ancient ecology, since traces of such lineages are long gone. But it’s unlikely that LUCA would have evolved complexity in isolation, the authors argue. Since its metabolism is consistent with both relying on and potentially supporting other microbes, LUCA was likely part of a broader ecosystem, from which its lineage was the sole survivor.

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"From these genes, they estimated that LUCA lived about 4.2 billion years ago — roughly 300 million years after the moon was formed from the collision of a Mars-size planet with Earth. This was a tumultuous time in our planet’s history. It likely took 100 million or 200 million years at minimum for the planet to settle down enough to support life.

"If that timeline is right, life had only a couple hundred million years to emerge and become fairly complex. LUCA and its early descendants would also have survived a period once thought too harsh for life, when Earth was continually bombarded with asteroids.

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"Not all scientists buy that LUCA is that old. “It’s very difficult to imagine that LUCA was living before 4 billion years ago,” said Patrick Forterre(opens a new tab), former head of microbiology at the Pasteur Institute, who co-organized the conference where the term “LUCA” was coined. He argues that Earth would have needed more time to cool down after the moon formed, and he is skeptical that we can accurately infer the pace of evolution at the time of LUCA."

Comment: this is not origin of life research but the implication of such an early start is amazing. This universe was prepared for life to appear quickly. With ecosystems forming early.