miércoles, 22 de septiembre de 2010
Life on Earth May Have Had an Icy Start
Cracks in ice could have served as a safe environment — much like a cell — for the first life on Earth to replicate and evolve.
A new study adds plausibility to the ‘RNA World’ hypothesis that argues life began with a single stranded molecule capable of self-replication.
“I always thought that the idea of an RNA world was exciting, but that RNA was a perverse choice of primordial material because it was hard to imagine chemical conditions under which they could survive on the early earth,” said biologist Philipp Holliger of MRC Laboratory of Molecular Biology in the United Kingdom, who led a study in Nature Communications Sept. 21.
“What we’ve found is that RNA would have been much happier in the ice than in hot hydrothermal vents, where it would have lasted only a few seconds,” Holliger said.Holliger was inspired to study how RNA replicates in icy conditions by a 2004 study that found when nucleotides — the building blocks of genetic code — are frozen in ice, they spontaneously assemble into random strands of RNA.
If nucleotides were present in the ice on early Earth, they could have formed uncountable combinations of these random genetic strands, many of which would have been meaningless. But a few of the strands might have contained the right genetic code to begin self-replication.
Over time, the replicating RNA strands would have mutated and changed with some of them surviving better than others, beginning the long chain of evolution towards more complex organisms.
By testing the process out in beakers, adding water, salts, RNA building blocks, and ribosomes — an RNA-derived molecule that serves as a center for the further RNA replication — Holliger found that liquid pockets ice would have served as an essential container for this process to occur. The cold would have also kept the molecules from degrading.
“It’s like the tortoise and the hare problem,” Holliger said. “The tortoise is slower, but it keeps on going, rather than falling apart. One thing that was available at the beginning of the Earth was time.”
A decade ago, this theory might have been dismissed because the early Earth was thought to be so hot and volcanic that ice couldn’t form. But more recently there has been evidence that the climate may have been more temperate, with areas of ice on the poles and at high altitudes, Holliger said.
If the theory of an ice RNA world is correct, it could dramatically change our search for life elsewhere in the universe.
“Ice is literally everywhere,” Holliger said . “If we can conceive of life arising and maybe thriving in ice it would considerably broaden the places to look for life, both extant and extinct.”