[meteorite-list] New Study Outlines 'Water World' Theory of Life's Origins
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 15 Apr 2014 17:01:11 -0700 (PDT)
New Study Outlines 'Water World' Theory of Life's Origins
Jet Propulsion Laboratory
April 15, 2014
Life took root more than four billion years ago on our nascent Earth,
a wetter and harsher place than now, bathed in sizzling ultraviolet rays.
What started out as simple cells ultimately transformed into slime molds,
frogs, elephants, humans and the rest of our planet's living kingdoms.
How did it all begin?
A new study from researchers at NASA's Jet Propulsion Laboratory in Pasadena,
Calif., and the Icy Worlds team at NASA's Astrobiology Institute, based
at NASA's Ames Research Center in Moffett Field, Calif., describes how
electrical energy naturally produced at the sea floor might have given
rise to life. While the scientists had already proposed this hypothesis
-- called "submarine alkaline hydrothermal emergence of life" -- the new
report assembles decades of field, laboratory and theoretical research
into a grand, unified picture.
According to the findings, which also can be thought of as the "water
world" theory, life may have begun inside warm, gentle springs on the
sea floor, at a time long ago when Earth's oceans churned across the entire
planet. This idea of hydrothermal vents as possible places for life's
origins was first proposed in 1980 by other researchers, who found them
on the sea floor near Cabo San Lucas, Mexico. Called "black smokers,"
those vents bubble with scalding hot, acidic fluids. In contrast, the
vents in the new study -- first hypothesized by scientist Michael Russell
of JPL in 1989 -- are gentler, cooler and percolate with alkaline fluids.
One such towering complex of these alkaline vents was found serendipitously
in the North Atlantic Ocean in 2000, and dubbed the Lost City.
"Life takes advantage of unbalanced states on the planet, which may have
been the case billions of years ago at the alkaline hydrothermal vents,"
said Russell. "Life is the process that resolves these disequilibria."
Russell is lead author of the new study, published in the April issue
of the journal Astrobiology.
Other theories of life's origins describe ponds, or "soups," of chemicals,
pockmarking Earth's battered, rocky surface. In some of those chemical
soup models, lightning or ultraviolet light is thought to have fueled
life in the ponds.
The water world theory from Russell and his team says that the warm, alkaline
hydrothermal vents maintained an unbalanced state with respect to the
surrounding ancient, acidic ocean -- one that could have provided so-called
free energy to drive the emergence of life. In fact, the vents could have
created two chemical imbalances. The first was a proton gradient, where
protons -- which are hydrogen ions -- were concentrated more on the outside
of the vent's chimneys, also called mineral membranes. The proton gradient
could have been tapped for energy -- something our own bodies do all the
time in cellular structures called mitochondria.
The second imbalance could have involved an electrical gradient between
the hydrothermal fluids and the ocean. Billions of years ago, when Earth
was young, its oceans were rich with carbon dioxide. When the carbon dioxide
from the ocean and fuels from the vent -- hydrogen and methane -- met
across the chimney wall, electrons may have been transferred. These reactions
could have produced more complex carbon-containing, or organic compounds
-- essential ingredients of life as we know it. Like proton gradients,
electron transfer processes occur regularly in mitochondria.
"Within these vents, we have a geological system that already does one
aspect of what life does," said Laurie Barge, second author of the study
at JPL. "Life lives off proton gradients and the transfer of electrons."
As is the case with all advanced life forms, enzymes are the key to making
chemical reactions happen. In our ancient oceans, minerals may have acted
like enzymes, interacting with chemicals swimming around and driving reactions.
In the water world theory, two different types of mineral "engines" might
have lined the walls of the chimney structures.
"These mineral engines may be compared to what's in modern cars," said
"They make life 'go' like the car engines by consuming fuel and expelling
exhaust. DNA and RNA, on the other hand, are more like the car's computers
because they guide processes rather than make them happen."
One of the tiny engines is thought to have used a mineral known as green
rust, allowing it to take advantage of the proton gradient to produce
a phosphate-containing molecule that stores energy. The other engine is
thought to have depended on a rare metal called molybdenum. This metal
also is at work in our bodies, in a variety of enzymes. It assists with
the transfer of two electrons at a time rather than the usual one, which
is useful in driving certain key chemical reactions.
"We call molybdenum the Douglas Adams element," said Russell, explaining
that the atomic number of molybdenum is 42, which also happens to be the
answer to the "ultimate question of life, the universe and everything"
in Adams' popular book, "The Hitchhiker's Guide to the Galaxy." Russell
joked, "Forty-two may in fact be one answer to the ultimate question of
The team's origins of life theory applies not just to Earth but also to
other wet, rocky worlds.
"Michael Russell's theory originated 25 years ago and, in that time, JPL
space missions have found strong evidence for liquid water oceans and
rocky sea floors on Europa and Enceladus," said Barge. "We have learned
much about the history of water on Mars, and soon we may find Earth-like
planets around faraway stars. By testing this origin-of-life hypothesis
in the lab at JPL, we may explain how life might have arisen on these
other places in our solar system or beyond, and also get an idea of how
to look for it."
For now, the ultimate question of whether the alkaline hydrothermal vents
are the hatcheries of life remains unanswered. Russell says the necessary
experiments are jaw-droppingly difficult to design and carry out, but
decades later, these are problems he and his team are still happy to tackle.
The California Institute of Technology in Pasadena manages JPL for NASA.
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin at jpl.nasa.gov
Received on Tue 15 Apr 2014 08:01:11 PM PDT