Back-arc Basin
The region between an island arc and the continental mainland, commonly with at least some oceanic crust on its floor.

Basalt
Extrusive igneous rock of gabbro composition; occurs as lava flows, sheeted dikes, shield volcanoes, or cinder cones.

Black Smoker
A chimney-like structure on the seafloor made of metal sulfides, out of which hot (~350°C) fluids that look like black smoke flow. The black color of the fluid is due to mineral particles within it.

Chemosynthesis
The process by which bacteria use energy from chemicals, such as hydrogen sulfide, to combine water and carbon dioxide to produce carbohydrates.

Chemotroph
An organism that gets energy from the oxidation of chemicals. At deep-sea hydrothermal vents, the chemotrophs oxidize hydrogen sulfide in the water that discharges from black smokers.

Chimney
A natural vent or opening in the Earth as a volcano.

Convergent Margin
Boundary along which two lithospheric plates are coming together, requiring one plate to pass beneath the other by subduction.

Dacite
Extrusive igneous rock consisting of intermediate plagioclase feldspar (about 50%), amphibole, pyroxene, and minor amounts of quartz.

Hydrogen Sulfide (H₂S)
A gas made up of hydrogen and sulfur with the characteristic odor of rotten eggs.

Hydrothermal Alteration
Chemical change in rocks and minerals caused by the action of hydrothermal (hot-water) solutions in volatiles that rise from a cooling magma chamber.

Hydrothermal Deposits
Deposits resulting from high-temperature water, either by altering existing rocks or by forming their own precipitates.

Knot
A unit of measure of speed. If you are traveling at a speed of one nautical mile per hour, you are said to be traveling at a speed of one know. (From How Stuff Works)

Mid-ocean Ridge
One of three major topographic divisions of the ocean basins, the central belt of submarine topography with a characteristic axial rift which marks a spreading plate boundary.

Nautical Mile
A nautical mile is based on the circumference of the Earth. If you were to cut the Earth in half at the equator, you could pick up one of the halves and look at the equator as a circle. You could divide that circle into 360 degrees. You could then divide a degree into 60 minutes. A minute of arc on the planet Earth is one nautical mile. This unit of measurement is used by all nations for air and sea travel. A nautical mile is equivalent to 1.1508 miles, 6,076 feet, or1,852 meters. (From How Stuff Works)

Photosynthesis
The production of organic matter by plants using water and carbon dioxide in the presence of chlorophyll and light; oxygen is released in the reaction.

Precipitation
The separation of minerals from a liquid or gas.

White Smoker
Chimneys with lighter colored minerals and lower fluid temperature.

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