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New
study outlines 'water world' theory of life's origins
New
study outlines 'water world' theory of life's origins
Date:
April 15,
2014
Source:
NASA/Jet Propulsion Laboratory
Summary:
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?
....................
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 Russell.
"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
life!"
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.
Story
Source:
The above
story is based on materials
provided by NASA/Jet
Propulsion Laboratory. Note: Materials may be edited for content and
length.
Journal
Reference:
- Michael J. Russell, Laura M. Barge, Rohit Bhartia, Dylan Bocanegra, Paul J. Bracher, Elbert Branscomb, Richard Kidd, Shawn McGlynn, David H. Meier, Wolfgang Nitschke, Takazo Shibuya, Steve Vance, Lauren White, Isik Kanik. The Drive to Life on Wet and Icy Worlds. Astrobiology, 2014; 14 (4): 308 DOI: 10.1089/ast.2013.1110
Cite This
Page:
NASA/Jet Propulsion Laboratory.
"New study outlines 'water world' theory of life's origins." ScienceDaily.
ScienceDaily, 15 April 2014.
<www.sciencedaily.com/releases/2014/04/140415195712.htm>.
