Download Hydrothermal Vents on the Mid

Hydrothermal Vents on the Mid-Ocean Ridge System
Very significant scientific discovery in 1979 on the Galapagos Spreading Center
and in the Gulf of California. Since then, vent systems have been observed on
nearly all ridge systems in all the worlds oceans.
How vents work:
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Seawater infiltrates the crust
(becoming groundwater)
This groundwater is heated by
–  The magmatic system, or
–  Exothermic chemical reactions
between the groundwater and crust
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Hot groundwater reacts with the
crust (dissolves rocks in chemical
reactions)
Hot, mineral laden groundwater is
then expelled out of the vent (hotspring).
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Vents build chimneys of mineral deposits
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Hot fluid laden with dissolved rock
–  Temps range from 80º - 700ºF
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This hot fluid hits cold seawater and
precipitates minerals building chimneys.
These vents circulate ocean-volumes of
seawater in 10s of thousands of years.
An interesting new vent type: Cold vents (~40ºC)
More videos
Current Hypothesis: Life evolved on
Earth at vents like these.
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Protected from harmful UV-B radiation
Abundant Energy available to generate life
Origin of Life on Earth: What we know
•  Oldest fossils are 3.5 Ga bacteria
–  First evidence for life come from
3.9 Ga sediments containing
apparent organic molecules with
abundant 12C - a product of
photosynthesis.
–  Life began (at the latest) 1 Ga after
planet condensation
•  Early atmosphere
–  Reducing environment (No O2)
–  No ozone, UV-B radiation!
–  Rich in CH4, NH3, CO2, N2
•  ‘Primordial Soup’...
video
Origin of Life: New Hypothesis
•  Carl Woese: new discovery
–  DNA of archeabacteria indicate
they are different than eubacteria
•  Why are they called Archeabacteria
(‘old bacteria’)?
–  They diverged from the bush of life
long ago (genetically, they are
varied and complex - i.e. ‘been
around a while)
–  Possibly back when life evolved on
Earth in the deep oceans.
•  Question: when did Earth first have
oceans?
–  4.4 Ga
–  Maybe life started long before first
fossil (3.5 Ga bacterial structures),
or before oldest evidence of life (3.9
Ga organic carbon)
Origin of Life: Traditional Concept
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Miller & Urey, 1953
–  Simulated a reducing atmosphere and
‘primordial’ ocean
–  added energy –  Lightening, volcanic, solar radiation, etc.
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Results:
–  Formed 12 of 20 amino acids in life
–  Other organic molecules too (HCN,
Formaldehyde)
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Later Fox’s experiments made polymers of
amino acids
–  Proteins
–  RNA!
–  Fatty acids & lipids - required for cells
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Conclusion: –  Not hard to make simple organic molecules
•  Problem with life evolving near surface
of Earth: that nasty UV-B!
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Note: 74 amino acids, and polymers found in
Chondritic meteorites. Origin of Life: New hypothesis
•  Amino acids around vents –  Extraterrestrial, or
–  Generated at vent (heat Energy) as in MillerUrey experiments
•  Why at vent and not surface?
–  Deep sea is shielded from UV-B!
–  Pyrite (FeS2) is abundant in this environment
and can serve as catalyst for replicating RNA
•  Huber & Wächtershäuser 1997
•  Current debate: did life originate at hot, or cold
vents?
–  Hot vents may be too hot, too energetic.
–  Cold vents can generate energy required as well
as fuels of life from chemical reactions within
the crust
•  Branscomb & Russell, 2012, Russell et al., 2010,
2012
Review Questions
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What is a submarine hydrothermal vent?
What is the source of heat for the vent system?
Why are submarine hydrothermal vents significant?
What is the first evidence for life on Earth and how old is it?
What can you conclude from the Fox-Miller-Urey experiments
regarding the origins of life?
–  What new discoveries have altered this hypothesis, and –  What is the favored hypothesis for the origins of life on Earth?