What better subject for the origin of a new year than the origin
of life itself? A new paper claims to have nailed down at last
the conditions, location and path by which life started, slicing
through two Gordian knots.
Knot No. 1 is the chick-and-egg problem of energy. Living things
burn energy at a furious rate to stay alive. Every time a bacterium
divides, it uses up 50 times its own mass of energy-currency
molecules (called ATP)-and that’s with efficient and specialized
modern protein machinery to do the job. When starting out, life
would have been a far more wasteful process, needing more energy,
yet would have had none of its modern machinery to harness or store
energy.
Knot No. 2 is entropy. Life uses energy to make order out of
chaos. So the putative location preferred by previous
evolutionists-Alexander Oparin’s primordial soup in Charles
Darwin’s “warm little pond” with a little lightning-is just too
unconstrained: Life would just keep dissolving away before it got
started.
Before the cell existed, life needed a controlled supply of
concentrated energy in a confined space. Comparing gene sequences
leads to the conclusion that at the very root of life’s family tree
lie the “chemi-osmotic” bacteria and archaea (single-celled
creatures like bacteria). These are microbes that effectively
charge their electrochemical batteries by converting carbon dioxide
into methane or the organic compound acetate.
Where did they originate? In 2000 explorers found vents in the
mid-Atlantic, the Lost City hydrothermal field, that are quite
unlike the better known hot, acidic “black smoker” deep-sea vents:
They last for much longer, are highly alkaline and modestly
warm.
Now Nick Lane of University College London and William Martin of
Heinrich Heine University in Düsseldorf, Germany, have concluded
that this environment carries uncanny echoes of life’s method of
storing energy.
Cells store energy by pumping charged “ions” usually of sodium
or hydrogen across membranes, effectively creating an electrical
voltage. This is a peculiar but universal feature of life, whose
ubiquity has never been explained. The scientists think it was
originally borrowed from vents like those at Lost City.
Four billion years ago, at such a vent, hot alkaline fluid rich
in hydrogen met acidic oceans saturated in carbon dioxide. There
would have been natural proton gradients across the thin
iron-nickel-sulfur walls of the vents, with a voltage very like the
membrane potential of modern chemi-osmotic microbes. The authors
write: “In our view-and given the near universality of proton
gradients across life-this is no coincidence.”
Today’s microbes that live at these hydrothermal vents use
proton gradients to add electrons to a protein called ferredoxin,
which in turn converts carbon dioxide into organic molecules needed
for growth. The vents’ rocks are riddled with interconnected
micro-pores, where these organic chemicals might once have
accumulated, some of them further accelerating the reaction.
Drs. Lane and Martin have an ingenious suggestion for how life
then became free-living. A geochemical proton gradient could freely
drive a biochemical sodium-ion pump, in effect allowing a membrane
to exclude sodium, forming another electrical energy storage
mechanism-one that would have been much more reliable as the first
leaky membranes began to seal off into cells. This would explain
why many primitive energy proteins use both sodium and hydrogen
(protons) indiscriminately, and why all living cells have less
sodium in them than seawater.
In effect, the energy reactions that happen chemically at
alkaline hydrothermal vents were borrowed and refined by living
cells, which is why there are so many chemical similarities
today.