Some scientists propose that in the beginning, geochemistry gave way to biochemistry — with no genetic material necessary. Only later did RNA and DNA appear.
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.
posted by f.sheikh