3. Layers of the Earth
• The core, which is approximately 7,000
kilometers in diameter and is located at the
• 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.
4. 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
5. The Mantle
• The mantle is almost 2,900 kilometers thick
and comprises about 83% of the Earth's
– The top layer of the upper mantle, 100 to 200
kilometers below surface, is called the
• The rocks in this upper portion of the mantle are more
rigid and brittle because of cooler temperatures and
6. The Mantle
– Below the upper mantle is the lower mantle that
extends from 670 to 2,900 kilometers below the
• 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
7. The Lithosphere
• Includes the crust and the upper most portion of
– 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
9. The Crust
• The topmost part of the lithosphere consists
– 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
10. Ocean Crust
• Ocean crust is thin and measures between 5 to 10
• It is also composed of basalt and has a density of
about 3.0 grams per cubic centimeter.
11. 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
12. 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
• Convection currents within the mantle cause
these plates to move slowly across the
13. Origin of the Earth
15. 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
• According to the most recent measurements
and observations, the Big Bang occurred
approximately 13.75 billion years ago
16. 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
– the first atomic nuclei only a few minutes after the
– Took thousands of years for electrons to combine
with them to create atoms.
17. 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.
• The Earth's outer solid layer, the lithosphere, is made
• A rock is a naturally occurring solid aggregate
of one or more minerals
– e.g., granite is a combination
of quartz, feldspar and biotite
19. Classification of Rocks
• Rocks are generally classified by mineral
and chemical composition, by the texture of the
constituent particles and by the processes that
types: igneous, sedimentary, and metamorphic.
• They are further classified according to particle
• The transformation of one rock type to another is
described by the geological model called the rock
20. Ingneous Rocks
• Igneous rocks are formed when
molten magma cools
– Plutonic or intrusive rocks result when magma
cools and crystallizes slowly within the Earth's
• example granite
– Volcanic or extrusive rocks result from magma
reaching the surface either as lava or fragmental
• examples pumice and basalt
24. 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.
25. Sedimentary Rocks
• Sedimentary rocks form at or near the Earth's
– Mud rocks comprise 65%
• E.g. shale
– sandstones 20 to 25%
– carbonate rocks 10 to 15%
• E.g., limestone
29. 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 Earth's 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