How A Rock At The Bottom Of The Sea May Have Started Life On Earth

Deep sea exploration vehicle near hydrothermal vent

fikretim from Magnific

Life on Earth may have started thanks to metals found at deep-sea vents, which helped the first cells run their chemistry before they could do it on their own. A new study reveals that the earliest cells inherited an incomplete set of life’s core chemical reactions from their environment and only completed their metabolism with help from these metals. This breakthrough tackles the biggest mystery in biology: how living things began carrying out the chemical processes of life before enzymes existed.

Two Branches, Two Different Solutions

Bacteria and archaea, the two main groups of simple living things, each developed their own ways to carry out the chemistry of life. Even though they needed to do the same things, they invented different enzymes to get the job done. The new study examined the DNA of hundreds of types of bacteria and archaea to see how they built their life chemistry.

Both bacteria and archaea can be traced back to a shared ancestor known as LUCA, or the Last Universal Common Ancestor. LUCA is the ancient organism from which all life on Earth descends. It lived billions of years ago and passed on basic cellular functions to every living thing today. If an enzyme is found in both bacteria and archaea, it likely existed in LUCA. If it’s found only in one group, it probably evolved after the two groups split.

When bacteria and archaea split, their core life chemistry wasn’t finished yet. Both groups faced the same challenges. Each found their own unique solutions. For example, the enzyme that helps make the amino acid alanine looks completely different in bacteria than in archaea. The same goes for enzymes involved in making aromatic amino acids, folate and riboflavin. In other words, bacteria and archaea came up with different tools to do the same jobs—even though the chemical reactions themselves are the same.

Metals Did the Work Before Enzymes Existed

Every chemical reaction in a modern cell has an enzyme that speeds it up. Without that, the reaction is too slow. If the earliest cells did not yet have the full set of enzymes, something else had to serve as a helper. That something was the rock itself.

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Metals like nickel, iron and cobalt, sitting on the walls of a deep-sea vent, act as chemical helpers. The study identified 37 core metabolic reactions that the metals undergo in the lab. Nickel alone performs the functions of at least ten enzymes and ten helper molecules in the pathway that converts carbon dioxide into organic matter. This pathway is one of the few things bacteria and archaea share, and it points straight back to the deep-sea vent.

These underwater vents are made of a rock called serpentinite. They form when seawater seeps down and reacts with iron- and magnesium-rich rocks far beneath the ocean floor. This reaction heats the water and produces hydrogen gas. It also leaves metals like nickel, iron and cobalt on the vent walls. Even now, these metals—the chemical starter kit for life—can still be found at the bottom of the Atlantic and Pacific oceans.

Metals aren’t the only key ingredient for life’s chemistry. Life runs on phosphate. Metabolism cannot run without it. Two-thirds of its intermediates carry phosphate groups. Cells use a molecule called ATP as their energy currency to move phosphate around. It was difficult to find a natural source of the high-energy phosphate group needed for life before ATP existed. This mystery puzzled researchers for decades. The recent study offers a solution: a natural cousin of phosphate, called phosphite. It forms in the same vents. When placed in water with a small amount of palladium, phosphite quietly does the work of ATP.

What This Says About the Order of Events

Overall, the story is that genes, translation and the genetic code were in place at LUCA. Metabolism was still being written. The two branches diverged, and each built out its metabolism with a partly overlapping, partly distinct toolkit. Human cells descend from within the archaeal branch and inherited a metabolism finished after the split. Life, in this sense, is a genome that pulled in a set of environmental reactions and gradually made them its own.

With this new understanding, deep-sea vents no longer look like exotic curiosities. They are the chemical grandparents, still active, still catalyzing the same reactions that started life more than four billion years ago.