Download the midocen ridge and the black smokers

FROM THE MIDOCEAN RIDGES TO
THE BLACK SMOKERS
What is it a midocean ridge?
A midocean ridge it’s due to the divergence between two plates (e.g. The African
plate and the South-American plate ).
The birth of the Atlantic Ocean (from Zullini)
The plates move away one from the other.
How long are the Oceanic spreading
ridges?
The Oceanic spreading ridges measure about 60.000 km in length. They occupy about 10% of
the earth’s surface.
The Mid-Atlantic Ridge
The Mid-Atlantic Ridge goes from the Greeenland in the north (80° N latitude) to the
end of South America in the south (55°S latitude).
How born a mid-ocean ridge
Due to the rise of the molten mantle, the lithosphere is broken resulting in the
formation of a narrow valley, called «rift» (as the «Great Rift Valley» in Africa). The rift
is surrounded by normal faults (red lines in the picture). From the rift exits the lava.
The Great Rift Valley in Africa (from Zullini).
The black triangles indicate the active vulcanos.
From the Rift Valley to the Ocean
If the spreading continues
there will be the formation of
a sea (e.g the Red Sea) and
finally an Ocean (e.g. the
Atlantic Ocean ).
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What happens in a midocean ridge
Along the ridges the molten rock (the magma) coming from the asthenosphere is
driven by convective motions breaking the oceanic crust and causing undersea
volcanic eruptions.
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Alvin and the «black smokers»
Deep-sea hydrothermal vents occur along the midocean ridges. Several different vents
have been discovered since the first site was found in 1977 near the Galapagos Islands
by earth scientists in the small research submersible ALVIN. One reason that relatively
few sites have been observed is that scientists have explored only a small portion of
the 50,000 kilometers of midocean ridges
Da
http://www.divediscover.
whoi.edu/
The «black smokers»
These black smokers are chimneylike structures made up of sulfur-bearing minerals or
sulfides that come from beneath Earth's crust. They form when hot (roughly 350¡C),
mineral-rich water flows out onto the ocean floor through the volcanic lava on a midocean ridge volcano.
The black smokers
Deep-sea hydrothermal vents support extraordinary ecosystems deep beneath the
surface of the oceans. These ecosystems are the only communities on Earth whose
immediate energy source is not sunlight. Life on Earth, and even possibly on other
planets, may have formed in environments similar to these.
http://www.youtube.com/watch?v=AlHJqA8YkoI&feature=player_detailpage gulf of
California 2003
black smoker
Sopra, agglomerato di
batteri
tube worms
The black smokers
Above: Instead of photosynthesis, vent ecosystems derive their energy from chemicals
in a process called "chemosynthesis." Both methods involve an energy source (1),
carbon dioxide (2), and water to produce sugars (3). Photosynthesis gives off oxygen
gas as a byproduct, while chemosynthesis produces sulfur (4). Image courtesy Woods
Hole Oceanographic Institution.
Life began next to the black smokers?
Unlike plants that rely on sunlight, bacteria living in and around
the dark vents extract their energy from hydrogen sulfide (HS)
and other molecules that billow out of the seafloor. Just like
plants, the bacteria use their energy to build sugars out of
carbon dioxide and water. Sugars then provide fuel and raw
material for the rest of the microbe's activities.
Astrobiologists are increasingly convinced that life on Earth itself
might have started in the sulfurous cauldron around
hydrothermal vents. Vent environments minimize oxygen and
radiation, which can damage primitive molecules. Indeed, many
of the primordial molecules needed to jump-start life could have
formed in the subsurface from the interaction of rock and
circulating hot water driven by hydrothermal systems.
The chemistry of a black smoker
Right: The chemistry of a
"black smoker." After sea
water seeps into the crust
(1), oxygen and potassium
(2) and then calcium, sulfate,
and magnesium (3) are
removed from the water. As
the water begins to heat up
(4), sodium, potassium, and
calcium dissolve from the
crust. Magma superheats
the water, dissolving iron,
zinc, copper, and sulfur (5).
The water then rises back to
the surface (6), where it
mixes with the cold
seawater, forming black
metal-sulfide compounds
(7). Image courtesy Woods
Hole Oceanographic
Institution.