FROM THE MIDOCEAN RIDGES TO THE BLACK SMOKERS. What is it a midocean ridge? A midocean ridge it’s...
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FROM THE MIDOCEAN RIDGES TO 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
What is it a midocean ridge? A midocean ridge its 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.
Slide 3
How long are the Oceanic spreading ridges? The Oceanic
spreading ridges measure about 60.000 km in length. They occupy
about 10% of the earths surface.
Slide 4
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 (55S latitude).
Slide 5
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.
How born a mid-ocean ridge The Great Rift Valley in Africa (from
Zullini). The black triangles indicate the active vulcanos.
Slide 6
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 ).
From the Rift Valley to the Ocean http://www.vialattea.net
Slide 7
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. What happens in a
midocean ridge http://try.iprase.tn.it
http://kidslink.bo.cnr.it
Slide 8
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/
Slide 9
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 350C),
mineral-rich water flows out onto the ocean floor through the
volcanic lava on a mid- ocean ridge volcano.
Slide 10
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_detailpagehttp://www.youtube.com/watch?v=AlHJqA8YkoI&feature=player_detailpage
gulf of California 2003 Sopra, agglomerato di batteri tube worms
black smoker
Slide 11
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.
Slide 12
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.
Slide 13
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.