COOKING UP PRIMAL STEW
Volcanic vents known as “black smokers” are found on the sea floor
in the world’s deepest oceans. They may represent environments where primitive life
first appeared billions of years ago on Earth, or on other planets. by Dennis Durband
S
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unlight does not exist at the base of
the Juan de Fuca Ridge –7,500 feet beneath
the surface of the Pacific Ocean. This cold,
dark, inhospitable environment lies 180 miles
west of the Washington-Oregon coastline.
The spot mutilates the definition of the word
“harsh.” The water temperature is just above
freezing, and the overbearing pressure is 3,350
pounds per square inch– more than enough to
flatten a mammal’s lungs.
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The Juan de Fuca Ridge
also features black smokers, volcanic vents that
spew water and chemicals superheated to 750
degrees Fahrenheit. Black smoke billows from
the vents, and the process actually builds columns
of rock.
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Amazingly, life exists here.
Tube worms, sea anemone, snails, crabs, blind
shrimp, microorganisms, and other types of marine
life flourish. They feed on bacteria and acidic
chemicals spewed by the black smokers.
▼
Black smokers are found throughout the world’s
mid-ocean ranges. The first black smoker was
discovered in 1977. John Holloway has built his own.
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ASU RESEARCH | Fall 2001
John C. Phillips photos
Geochemists John
Holloway, Peggy O’Day,
and graduate students
such as Ken Vogelsonger
brew batches of primal
stew in an ASU laboratory
named Depths of the Earth.
Photo courtesy Woods Hole Oceanographic Institute
“It’s a lot more challenging to think about the chemistry of natural systems,
and to understand their complexity.” –P E G G Y O ’ D AY
Holloway is geochemistry professor at
Arizona State University. He calls his laboratory “Depths of the Earth, Inc.”
Inside, the light is bright and the pressure is no threat to human lungs.
Holloway’s simulated black smokers are steel tubes. He manipulates the
temperature to simulate emissions.
At the Juan de Fuca Ridge, sulfide minerals crystallize onto volcanic
rocks where hot water flows from vents. Hollow chimneys grow as
a result of the constant crystallization. These black smokers occur on
sulfide mounds in vent fields ranging in size from a kitchen table to a
tennis court. The chimneys resemble underwater versions of hoodoo
rock formations found throughout the American Southwest.
For 35 years, Holloway has studied the interplay between gases and
rocks to determine how rock melts into magma, where magma flows,
and how water trapped in rising magma builds enough steam to blow the
tops off volcanoes. His aim is to understand the conditions found in the
interior of the Earth, as well as Earth-like planets.
“Our purpose is to understand the nature of the minerals below the
planet’s surface,” Holloway says. “What are their crystal structures and
chemical compositions? How do the minerals react with each other with
changing pressure, depth, and temperature? What are the conditions that
cause rocks in the Earth’s interior to melt? And how do those melts form
magmas that may reach the surface as lava flows or explosive volcanic
eruptions?
The interest in black smokers is recent. Holloway and ASU geology
Professor Peggy O’Day collaborate to study the geochemistry of black
smokers. Their work also includes the new field of astrobiology– the
attempt to understand life’s beginnings by placing it in its cosmic context.
O’Day and Holloway create small-scale models in the laboratory
to mimic deep-sea thermal vents. They want to help scientists decide
whether or not these thermal areas gave birth to life itself.
The height and shape of black smokers is variable and depends
on flow rate and the amount of time they have had to build. Young black
smokers may be only a few centimeters tall. Large structures may be tens
of meters high, such as the black smokers at the Juan de Fuca Ridge.
Smokers with a large central flow vent tend to be tall and thin.
Those with more diffuse outflow channels tend to be mound-like.
Many forms of ocean life that dwell near black smokers actually
pollute the vents. They prevent scientists from identifying the pure chemical components being spewed from the vents. To translate chemical
samples taken from the vents back into the original gases that rise up from
below the Earth, scientists need to study the gases in a laboratory.
Are these ocean vents capable of brewing the chemical ingredients
of life? To find out, the ASU scientists match the magma-producing pressures of Earth just below the seafloor. They heat artificial seawater to 750
degrees Fahrenheit as it rises through a simulated sea floor machine.
They want to develop gas chemistry profiles that might help scientists
understand the stages of a volcano.
Holloway’s lab does not use real seawater. The scientists make it by
adding “Instant Ocean” to distilled water to develop a perfect duplicate
of seawater. The powdered mixture of salts is sold in pet stores for seawater aquariums.
“This research is a lot more interesting than doing just chemistry as
a pure science,” O’Day says. “It’s a lot more challenging to think about
the chemistry of natural systems, and to understand their complexity.
I’m interested in combining what I know about the Earth and Earth
sciences with chemistry.”
Holloway says that experimentation in organic synthesis is a new
area of study, as it relates to black smokers. People do dive down to black
smokers, but they can’t study conditions before life arose. Although
no one has yet drilled into the subsurface of active black smokers,
O’Day says there is most likely some interesting chemistry involved.
The ASU researchers are developing laboratory systems that allow
them to intimately study extreme chemical conditions and understand
the biology and physics of fluids. They want to learn new ways of understanding organic systems.
To some extent, the results of laboratory experiments are always
dictated by the materials used and conditions imposed on the reaction.
Since no one really knows what early planetary environments were like
on Earth, or on other planets, scientists can pick and choose the reactants
they study in the lab. The ASU scientists try to ground their experiments
in what they think might be geologically plausible conditions.
“We use modern seafloor environments as kind of an analog
of an environment that we see going on, and that probably did go on in
the past,” O’Day says. “We try to tie our experiments as closely as we
can to current geologic hypotheses.”
The confluence of chemical, geological, and biological research is a
strength that sets ASU apart from many other universities, says Jonathan
Fink, a geologist, volcano expert, and ASU ’s vice provost for research.
“This kind of research makes ASU an especially exciting place
for graduate students interested in interdisciplinary studies. John and
Peggy mix up a stew of chemicals, pressure, and temperature, and then
look for the appearance of any organic compounds, the precursors
to life,” Fink says. “Similar processes may also be taking place at the
bottom of a global ocean believed to exist beneath the icy crust on
Jupiter’s moon Europa.”
The National Science Foundation supports research at the “Depths of the Earth” laboratory.
For more information, contact John R. Holloway, Ph.D., or Peggy A. O’Day, Ph.D.,
Geological Sciences, College of Liberal Arts and Sciences, 480.965.5081.
Send e-mail to [email protected]
ASU RESEARCH | Fall 2001
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