Did life emerge on Earth twice? Scientists find surprising evidence
The common descent theory is being called into question (photo: Pexels)
A new study by scientists at Heinrich Heine University Düsseldorf suggests that the transition from nonliving chemical matter to fully living organisms may have occurred on Earth twice, independently of each other, according to Science Advances.
One genetic root, two origins of life
For a long time, the scientific community believed that all living organisms shared a single common ancestor—the so-called LUCA (Last Universal Common Ancestor).
However, a new analysis of enzymes and fundamental chemical reactions revealed significant differences between the two main branches of early life—bacteria and archaea (prokaryotes).
According to study leader William Martin, enzymes that catalyze the same basic metabolic reactions are structurally different in bacteria and archaea.
This suggests that the two groups developed their own autonomous metabolic systems independently of each other, after diverging from a common ancestor.
Key study findings
The common ancestor LUCA was not fully "alive": It possessed enzymes for only half of the necessary metabolic reactions, while naturally occurring environmental metals catalyzed the other half.
Parallel evolution: Bacteria and archaea independently evolved their own protein enzymes to replace inorganic metals, thereby becoming fully autonomous cells.
One code, but different metabolism: Humanity may be looking at one origin of the genetic code, but two separate origins of fully developed cellular life.
What played most important role?
Scientists suggest that the first chemical reactions that eventually led to life took place under extreme conditions—near underwater hydrothermal vents.
In the early stages, metals such as palladium present in the water acted as catalysts, converting hydrogen, ammonia, and carbon dioxide into organic molecules.
In addition, the researchers addressed a longstanding scientific question about the energy source for primitive metabolism.
Modern cells use ATP for this purpose, but ATP itself is a product of complex enzymatic processes.
Experiments showed that in the early stages, its role may have been played by phosphite—a form of phosphorus that naturally occurs near hydrothermal vents and readily participates in reactions without enzymes.
If the scientists' conclusions are confirmed by further research, the traditional "tree of life" may have to be rewritten: instead of a single common trunk, it may have two separate origins that emerged before the first fully developed cells appeared.
