The community of proto-genomes quickly shared innovations among themselves, in Woese's new view, and the system evolved by producing more complicated proteins, the working parts of the cell. The genetic code was at first translated rather inaccurately, so the proteins it produced were short and limited in capability. But the code became more accurate, and the proteins more complex, driven by the advantage that more capable proteins conferred. At a certain stage of complexity, design decisions may have limited cells' ability to exchange genes, and the ancestral pool would have split into the three kingdoms seen today, the new theory suggests. It is possible, of course, that evolution's early traces have become too faint to decipher.
Life seems to have popped up on earth with surprising rapidity.
The planet is generally thought to have become habitable only some 3.85 billion years ago, after the oceans stopped boiling off from titanic asteroid impacts. Yet by 3.5 billion years ago, according to the earliest fossil records, living cells were flourishing, and there are indirect signs of life even earlier, in rocks that are 3.8 billion years old. This narrowing window of time may be less embarrassing than it seems. Biologists are warming to the view that the emergence of life from chemical precursors is a quite probable event which does not require billions of years to get under way. Still, many more years of evolution presumably passed before the universal ancestor, a quite sophisticated genetic system, attained its final form.