People study science to learn about the physical world.

Scoria are bomb-sized (greater than 64 mm across) pyroclastic fragments that are formed as blobs of lava cool when they are blasted through the air. Scoria are filled with cavities formed by trapped air bubbles.

 seafloor spreading
Seafloor spreading is the movement of two oceanic plates away from each other, which results in the formation of new oceanic crust and a mid-ocean ridge.



A seamount is an underwater mountain that rises at least 1000 meters above the sea floor. Some seamounts rise above the water's surface. Most seamounts are volcanic in orgin; only a few are non-volcanic (caused by uplifting).

 sedimentary rock

Sedimentary rock is rock that has formed from sediment. Most fossils are found sedimentary rock.

A seismigraph is a device that records and measures seismic waves (vibrations in the Earth), like those from earthquakes.


 shield volcano
A shield volcano is a volcano that has gently sloping sides. Shield volcanoes are composed mostly of
basalt (whose lava flows easily and quickly). The biggest volcanoes on Earth (like those on the islands of Hawaii) are shield volcanoes.
 shocked quartz
Shocked quartz is quartz that has undergone deformation due to extreme pressure and heat. It has been found in the layer that marks the
K-T boundary, leading credence to the Alvarez impact theory.

A skylight is a an opening in the roof of a lava tube. Skylights are formed either when part of the roof collapses or as a gap in the tube when the tube initally forms.


 side vent
A side vent is an opening in the side of a volcano through which volcanic materials (like lava, gases, and pyroclastic debris) erupt.
Silica is a very common mineral composed of silicon and oxygen (SiO2). Silicates make up about 95% of the
Earth's crust.
Silicates are minerals composed of silicon and oxygen with one or more other elements. Silicates make up about 95% of the
Earth's crust.



The sky on Earth appears blue because our
atmosphere scatters the blue colors from the sunlight (which consists of all colors of light). The sky on planets with a different atmospheric composition would appear to be a different color.

A solid is one
phase of matter, a phase in which the molecules are very close together and cannot move around.

 spreading ridge
A spreading ridge is an area of the ocean floor in which new crust is being formed as magma erupts.


 states of matter

Matter can exist in four states or phases (
solid, liquid, gas, and plasma) and a few other extreme phases (like critical fluids and degenerate gases). The phase diagram of water (above) shows its phase at various temperatures and pressures.
Stishovite is a very dense form of quartz that has only been found in
meteorite impact craters, in which quartz has undergone high-pressure shock.
A stratovolcano is a
composite volcano.



A subduction is a phenomenon in which one part of the Earth's crust (a plate) is pushed underneath another plate as two plates collide. The descending crust melts as it is pushed deep into the
Earth's mantle. Subduction destroys crust and recycles it back into the mantle.
 subduction zone
A subduction zone is an area on a planet's crust in which the edge of an oceanic
continental plate is being pushed beneath another plate.


Subliming is when a material goes directly from being a solid to being a gas (it skips the liquid phase altogether).

A supervolcano is an enormous volcano that is an order of magnitude larger than ordinary volcanoes. A supervolcano occurs when a huge magma chamber in the Earth's crust erupts after being under great pressure, causing a large caldera to form as the land over the magma chamber collaspses. This type of eruption is probably able to cause a major climate change and a
mass extinction as it ejects dust, debris, and caustic gases into the atmosphere. Supervolcanos do not look like the familiar cone-shaped volcano - a supervolcano looks like a huge collapsed crater. Yellowstone National Park (in Wyoming and Montana, USA) is a supervolcano70 km long and 30 km wide; it is due to erupt soon (in terms of geological time).


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