A New Study Points to Two Origins of Life on Earth by Tracing Early Chemical Reactions in Single-Celled Organisms
Skip to main content
Subscribe to Smithsonian magazine and get a FREE tote.
Science | August 5, 2026
A New Study Points to Two Origins of Life on Earth by Tracing Early Chemical Reactions in Single-Celled Organisms
The work challenges the assumption that all life descended from one free-living cell. Instead, it suggests that two microbial lineages, the bacteria and archaea, evolved independently from a primordial, nonliving ancestor
A digital illustration of typical prokaryotes—cells that do not contain a nucleus. Bacteria and archaea are the two kinds of prokaryotes on Earth, and their ancestors were the first organisms to evolve.<br>Mark Garlick / Science Photo Library via Getty Images
A digital illustration of typical prokaryotes—cells that do not contain a nucleus. Bacteria and archaea are the two kinds of prokaryotes on Earth, and their ancestors were the first organisms to evolve.<br>Mark Garlick / Science Photo Library via Getty Images
Among biologists, few questions have been debated as fiercely as the origin of life. How did self-sustaining organisms, capable of transforming molecules to capture energy, arise on the primitive Earth?
Before any cells existed, scientists suspect chemical reactions occurred around deep-sea hydrothermal vents, where heat and high pressures led to spontaneous chemistry that was sped up, or catalyzed, by metals in Earth’s crust. One possibility for the origin of life is that, over time, these relatively simple geochemical reactions evolved into the reactions that create the building blocks of life.
Living creatures rely on a core network of about 400 metabolic reactions that are catalyzed by proteins known as enzymes. This “core metabolism” creates energy and makes key materials for cells, like nucleic acids, amino acids and vitamins.
Now, a team of researchers has retraced the steps for how this essential metabolic network was assembled, in a paper published today in Science Advances. One of their most striking findings: Life on Earth likely evolved not once, but twice.
“This just opens up a whole lot of questions, in terms of what is alive, what is life, what is possible, and what we might find elsewhere,” says senior author William Martin, an evolutionary biologist at the University of Düsseldorf in Germany.
Microscopic archaea dwell in the hot waters of Midway Geyser Basin in Yellowstone National Park, bringing color to the landscape.
Wing-Chi Poon via Wikimedia Commons under CC BY-SA 2.5
All organisms alive today descend from the last universal common ancestor (LUCA) that likely dwelled in the early oceans. This mysterious ancestor, the new study suggests, was still reliant on its environment to conduct metabolism. Rather than fueling its energy-producing reactions on its own with enzymes, LUCA depended on small organic molecules and metals in the environment to conduct about half of the core metabolic reactions, the researchers found. Then, over time, some of these metals were replaced with more specific and efficient enzymes as the proteins evolved to do the same jobs.
“What’s so cool about this is we’re probing a phase of evolution where new enzyme activities are still arising, replacing geochemical reactions, and giving rise to coalescence of metabolism in the ancestors of archaea and bacteria,” Martin says.
Archaea and bacteria are two of the three domains of life, and these microbes arose early in Earth’s history. The third domain, eukaryotes—the one that animals, plants and all organisms with nucleus-containing cells belong to—evolved later, from a hybrid of the first two groups.
For many years, scientists contemplated three possible scenarios for the origin of life: Either bacteria evolved from archaea, archaea evolved from bacteria, or both independently evolved from LUCA. The new study makes the argument that the last possibility is the most likely one.
Quick fact: Archaea and bacteria
While bacteria live in diverse environments, archaea thrive under extreme conditions, like high heat and acidity.
Scientists can illuminate how bacteria and archaea emerged by comparing when their ancestors evolved certain traits and pinning down which of those traits might have been inherited from LUCA. Earlier work did this with ribosomes, the parts of a cell that produce proteins. It showed that LUCA had primitive ribosomes that were composed of 33 proteins. Then, from LUCA, the bacterial lineage evolved 21 unique ribosomal proteins, while the archaeal lineage evolved 29 unique ribosomal proteins. Each lineage, in essence, independently continued tweaking and enhancing how its ribosomes worked.
For their latest investigation focused on reconstructing metabolism, Martin’s team took a similar approach. This time, they examined the genes for metabolic enzymes in modern bacteria and archaea to reconstruct their evolutionary history. Just as some...