The Earth: A Basic Intro- Part II Dr. Mark McGinleyHonors College and Department of Biological Sciences Texas Tech University
Layers of the Earth
Layers of the Earth• The core, which is approximately 7,000 kilometers in diameter and is located at the Earths center.• The mantle, which surrounds the core and has a thickness of 2,900 kilometers.• The crust, which floats on top of the mantle. It is composed of basalt rich oceanic crust and granitic rich continental crust. http://www.eoearth.org/article/Structure_of_the_Earth
The Core• The core is a layer rich in iron and nickel – The inner core is theorized to be solid with a density of about 13 grams per cubic centimeter and a radius of about 1,220 kilometers. – The outer core is liquid and has a density of about 11 grams per cubic centimeter. It surrounds the inner core and has an average thickness of about 2,250 kilometers.
The Mantle• The mantle is almost 2,900 kilometers thick and comprises about 83% of the Earths volume. – The top layer of the upper mantle, 100 to 200 kilometers below surface, is called the asthenosphere. • The rocks in this upper portion of the mantle are more rigid and brittle because of cooler temperatures and lower pressures.
The Mantle– Below the upper mantle is the lower mantle that extends from 670 to 2,900 kilometers below the Earths surface. • This layer is hot and plastic. The higher pressure in this layer causes the formation of minerals that are different from those of the upper mantle
The Lithosphere• Includes the crust and the upper most portion of the asthenosphere. – This layer is about 100 kilometers thick and has the ability to glide over the rest of the upper mantle. – Because of increasing temperature and pressure, deeper portions of the lithosphere are capable of plastic flow over geologic time. – The lithosphere is also the zone of earthquakes, mountain building, volcanoes, and continental drift.
The Crust• The topmost part of the lithosphere consists of crust. – This material is cool, rigid, and brittle.• Two types of crust – oceanic crust and continental crust – Both of these types of crust are less dense than the rock found in the underlying upper mantle layer.
Ocean Crust• Ocean crust is thin and measures between 5 to 10 kilometers thick.• It is also composed of basalt and has a density of about 3.0 grams per cubic centimeter.
Continental Crust• The continental crust is 20 to 70 kilometers thick and composed mainly of lighter granite.• The density of continental crust is about 2.7 grams per cubic centimeter.• It is thinnest in areas like the Rift Valleys of East Africa and in an area known as the Basin and Range Province in the western United States (centered in Nevada this area is about 1,500 kilometers wide and runs about 4,000 kilometers North/South).
Continental Crust• Continental crust is thickest beneath mountain ranges and extends into the mantle. Both of these crust types are composed of numerous tectonic plates that float on top of the mantle.• Convection currents within the mantle cause these plates to move slowly across the asthenosphere.
Origin of the Earth• http://www.natgeoeducationvideo.com/film/ 1140/the-structure-of-the-universe• http://www.natgeoeducationvideo.com/film/ 1170/the-origin-of-earth
The Big Bang
The Big Bang• According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly.• This rapid expansion caused the Universe to cool and resulted in its present continuously expanding state.• According to the most recent measurements and observations, the Big Bang occurred approximately 13.75 billion years ago Wikipedia
The Big Bang• After its initial expansion the Universe cooled sufficiently to allow energy to be converted into various subatomic particles, including protons, neutrons, and ele ctrons. – the first atomic nuclei only a few minutes after the Big Bang – Took thousands of years for electrons to combine with them to create atoms.
The Big Bang– The first element produced was hydrogen, along with traces of helium and lithium.– Giant clouds of these primordial elements would coalesce through gravity to form stars and galaxies, and the heavier elements would be synthesized either within stars or during supernovae.
Rocks• The Earths outer solid layer, the lithosphere, is made of rock.• A rock is a naturally occurring solid aggregate of one or more minerals – e.g., granite is a combination of quartz, feldspar and biotite Wikipedia
Classification of Rocks• Rocks are generally classified by mineral and chemical composition, by the texture of the constituent particles and by the processes that formed them.• Three types: igneous, sedimentary, and metamorphic.• They are further classified according to particle size.• The transformation of one rock type to another is described by the geological model called the rock cycle.
Ingneous Rocks• Igneous rocks are formed when molten magma cools – Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earths crust • example granite – Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta • examples pumice and basalt
Sedimentary Rocks• Sedimentary rocks are formed by deposition of either sediments, organic matter, or chemical precipitates, followed by compaction of the particulate matter and cementation during a process known as diagenesis.
Sedimentary Rocks• Sedimentary rocks form at or near the Earths surface. – Mud rocks comprise 65% • E.g. shale – sandstones 20 to 25% – carbonate rocks 10 to 15% • E.g., limestone
Metamorphic Rocks• Metamorphic rocks are formed by subjecting any rock type to different temperature and pressure conditions than those in which the original rock was formed.• These temperatures and pressures are always higher than those at the Earths surface and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals – e.g. by recrystallization