Sima is the name for the lower layer of the Earth’s crust. This layer is made of rocks rich in silicates and magnesium minerals. Typically the sima when it comes to the surface is basalt, so sometimes this layer is called the ‘basalt layer’ of the crust. The sima layer is also called the ‘basal crust’ or ‘basal layer’ because it is the lowest layer of the crust. Because the ocean floors are mainly sima, it is also sometimes called the ‘oceanic crust’.

The name ’sima’ was taken from the first two letters of silica and of magnesium. Comparable is the name ‘Sial’ which is the name for the upper layer of the Earth’s crust.

Petrology

The sima has a higher density (2800 to 3300 kg/m³) than the sial, which is due to increased amounts of iron and magnesium, and decreased amounts of aluminium. When the denser sima comes to the surface it forms mafic rocks, or rocks with mafic minerals. The most dense sima has less silica and forms ultramafic rocks.

References

• Bates, R.L., and Jackson, J.A., (1987) Glossary of geology American Geological Institute, Alexandria, Virginia.
• Dilek, Y. and Newcomb, S. (eds.) (2003) Ophiolite Concept and the Evolution of Geological Thought Geological Society of America Special Paper 373, Boulder, Colorado.

See also

• Sial
• KREEP
• Nife

References

• Magnetic Mars :: Astrobiology Magazine - earth science - evolution Summary (Oct 21, 2005): NASA scientists have discovered additional evidence that Mars once underwent plate tectonics, slow movement of the planet's crust,
• Geology of Mars - Wikipedia, the free encyclopedia Although Mars today has no global-scale intrinsic magnetic field, observations have been interpreted as showing that parts of the planet's crust have been
• NASA - New Map Provides More Evidence Mars Once Like Earth NASA scientists have discovered additional evidence that Mars once underwent plate tectonics, slow movement of the planet's crust, like the present-day
• Drak - The World of the Dragoncats Due to trapped gasses that formed within the planet's crust during its formation, its crust is honeycombed with tunnels and chambers.
• Mars@Everything2.com The reason that Mars is red is because of the high iron content of the planet's crust. Over the years, this has reacted with oxygen and water in the air to
• Science Journal - WSJ.com That creates a teeter-totter effect, further destabilizing the planet's crust. "Recent findings reinforce the idea that the solid earth and the climate are
• BNSC - The surface of Mars These formed craters all over its crust, many of which are still visible today. Molten rock from the meteorites forced its way through the planet's crust,
• Planetary Geology Because a planet's geology is inextricably linked to such basic attributes . potassium atoms may represent gases diffusing up through the planet's crust.
• SkyandTelescope.com - Homepage News - Swimming a Salty Sea This disparity is due to tectonic activity, which, as it sucks ocean water beneath the planet's crust, tends to pull magnesium out of the water.
• World Mysteries - Science Mysteries - Asteroid Belt - The Exploded Meteors and comets are debris from the former planet's crust, which was blown by the explosion's force so far into space that they were not attracted by the