[ExI] Luca, the Ancestor of All Living Things
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Thu Jul 28 21:56:18 UTC 2016
Meet Luca, the Ancestor of All Living Things
By Nicholas Wade July 25, 2016
A surprisingly specific genetic portrait of the ancestor of all living
things has been generated by scientists who say that the likeness
sheds considerable light on the mystery of how life first emerged on
The nature of the earliest ancestor of all living things has long been
uncertain because the three great domains of life seemed to have no
common point of origin. The domains are those of the bacteria, the
archaea and the eukaryotes. Archaea are bacteria-like organisms but
with a different metabolism, and the eukaryotes include all plants and
Specialists have recently come to believe that the bacteria and
archaea were the two earliest domains, with the eukaryotes emerging
later. That opened the way for a group of evolutionary biologists, led
by William F. Martin of Heinrich Heine University in Düsseldorf,
Germany, to try to discern the nature of the organism from which the
bacterial and archaeal domains emerged.
Genes are adapted to an organism’s environment. So Dr. Martin hoped
that by pinpointing the genes likely to have been present in Luca, he
would also get a glimpse of where and how Luca lived. “I was
flabbergasted at the result, I couldn’t believe it,” he said.
The 355 genes pointed quite precisely to an organism that lived in the
conditions found in deep sea vents, the gassy, metal-laden, intensely
hot plumes caused by seawater interacting with magma erupting through
the ocean floor.
Dr. Sutherland and others have no quarrel with Luca’s being traced
back to deep sea vents. But that does not mean life originated there,
they say. Life could have originated anywhere and later been confined
to a deep sea environment because of some catastrophic event like the
Late Heavy Bombardment, which occurred 4 billion to 3.8 billion years
ago. This was a rain of meteorites that crashed into Earth with such
force that the oceans were boiled off into an incandescent mist.
Life is so complex it seems to need many millions of years to evolve.
Yet evidence for the earliest life dates to 3.8 billion years ago, as
if it emerged almost the minute the bombardment ceased. A refuge in
the deep ocean during the bombardment would allow a longer period in
which life could have evolved. But chemists like Dr. Sutherland say
they are uneasy about getting prebiotic chemistry to work in an ocean,
which powerfully dilutes chemical components before they can assemble
into the complex molecules of life.
Dr. Sutherland, working from basic principles of chemistry, has found
that ultraviolet light from the sun is an essential energy source to
get the right reactions underway, and therefore that land-based pools,
not the ocean, are the most likely environment in which life began.
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