Apr 11, 2025 07:25 PM
https://knowablemagazine.org/content/art...lism-first
INTRO: Four billion years ago, our planet was water and barren rock. Out of this, some mighty complicated chemistry bubbled up, perhaps in a pond or a deep ocean vent. Eventually, that chemistry got wrapped in membranes, a primitive cell developed and life emerged from the ooze.
But how? Among the many mysteries is a chicken-and-egg problem to solve. The proteins called enzymes that get chemical reactions going inside cells are created from instructions carried in genetic material: DNA or RNA. But at the start, those molecules weren’t around: To make them, you need enzymes.
So what got things going?
One idea long floated by scientists is that genetic material came first — in the form of a molecule called RNA, a close cousin to DNA. RNA’s beauty is its versatility: It can catalyze chemical reactions and store genetic information. So perhaps in a pond on Earth’s surface, molecules were concentrated by evaporation and then linked together to form the first RNA strands.
But so far, scientists have not been able to create RNA molecules in experiments mimicking the soups of simple chemicals that would have been around on early Earth. “There have been reports of how to do it, but they always seem a little bit contrived,” says Albert Fahrenbach, an organic chemist at the University of New South Wales in Sydney — though he adds that proponents say such trickiness is only to be expected.
It’s difficult to imagine that a system of self-replicating chains of RNA could have organized spontaneously, says Robert Pascal, a chemist who works on the origins and emergence of life at Aix-Marseille University in France. “I think that really, nobody believes now that it could have been possible.”
Another possibility is that biochemistry came first — it evolved as geochemistry, outside of cells. Chemical reactions would have proceeded without enzymes at the start, very slowly. Reactions would inch forward because they were thermodynamically favored, and possibly sped up by heat or metals. Later on, primitive enzymes developed, further speeding up that primordial chemistry of life.
Over geological time, geochemistry would have become faster and more elaborate, adding on new reactions. Somewhere along the way, cell membranes and a system of heredity, in the form of RNA or DNA, would have arisen. Geochemistry would morph into biochemistry.
This second hypothesis lacked key experimental evidence until fairly recently. But in the last few years, researchers have been able to test in the lab vast combinations of chemical mixtures and conditions and identified ways to replicate core metabolic reactions that take place in cells — all without enzymes.
The idea that geochemistry preceded biochemistry is “a really powerful idea,” says Susan Lang, a geochemist at Woods Hole Oceanographic Institution in Massachusetts. “And I think that [the scientists] have brought a lot of evidence to bear to support that idea.” (MORE - details)
INTRO: Four billion years ago, our planet was water and barren rock. Out of this, some mighty complicated chemistry bubbled up, perhaps in a pond or a deep ocean vent. Eventually, that chemistry got wrapped in membranes, a primitive cell developed and life emerged from the ooze.
But how? Among the many mysteries is a chicken-and-egg problem to solve. The proteins called enzymes that get chemical reactions going inside cells are created from instructions carried in genetic material: DNA or RNA. But at the start, those molecules weren’t around: To make them, you need enzymes.
So what got things going?
One idea long floated by scientists is that genetic material came first — in the form of a molecule called RNA, a close cousin to DNA. RNA’s beauty is its versatility: It can catalyze chemical reactions and store genetic information. So perhaps in a pond on Earth’s surface, molecules were concentrated by evaporation and then linked together to form the first RNA strands.
But so far, scientists have not been able to create RNA molecules in experiments mimicking the soups of simple chemicals that would have been around on early Earth. “There have been reports of how to do it, but they always seem a little bit contrived,” says Albert Fahrenbach, an organic chemist at the University of New South Wales in Sydney — though he adds that proponents say such trickiness is only to be expected.
It’s difficult to imagine that a system of self-replicating chains of RNA could have organized spontaneously, says Robert Pascal, a chemist who works on the origins and emergence of life at Aix-Marseille University in France. “I think that really, nobody believes now that it could have been possible.”
Another possibility is that biochemistry came first — it evolved as geochemistry, outside of cells. Chemical reactions would have proceeded without enzymes at the start, very slowly. Reactions would inch forward because they were thermodynamically favored, and possibly sped up by heat or metals. Later on, primitive enzymes developed, further speeding up that primordial chemistry of life.
Over geological time, geochemistry would have become faster and more elaborate, adding on new reactions. Somewhere along the way, cell membranes and a system of heredity, in the form of RNA or DNA, would have arisen. Geochemistry would morph into biochemistry.
This second hypothesis lacked key experimental evidence until fairly recently. But in the last few years, researchers have been able to test in the lab vast combinations of chemical mixtures and conditions and identified ways to replicate core metabolic reactions that take place in cells — all without enzymes.
The idea that geochemistry preceded biochemistry is “a really powerful idea,” says Susan Lang, a geochemist at Woods Hole Oceanographic Institution in Massachusetts. “And I think that [the scientists] have brought a lot of evidence to bear to support that idea.” (MORE - details)