2. PLATE TECTONICS
Tectonic plates are huge and irregularly shaped pieces of
solid rocks which composed both the continental and the
oceanic lithosphere.
These plates are in constant motion and travel few
centimeters each year. In fact, the Pacific plate has been
moving horizontally past along the North American Plate
for 10 million years at an average rate of 5cm per year.
These plates are responsible for the changes in the structure
of the Earth since the beginning of time.
5. What is a geosphere?
The geosphere is the Earth itself: the rocks, minerals, and
landforms of the surface and interior.
Beyond these parts, the geosphere is about processes. The process
of the rock cycle such as metamorphism, melting and
solidification, weathering, erosion, deposition, and burial are
responsible for the constant recycling of rocks on Earth between
sedimentary, igneous, and metamorphic states.
Sedimentary rocks are formed via weathering and transport of
existing rocks, and then deposition, cementation, and compaction into
sedimentary rock.
Igneous rocks are formed by the cooling and crystallization of molten
rock.
Metamorphic rocks are formed when heat or pressure is applied to
other rocks.
9. LAYERS OF THE EARTH
The crust is the outermost and thinnest layer. It is composed of
hard strong rocks because it is relatively cool. The crust consists of
continental and oceanic crust.
The mantle is the layer that lies directly beneath the crust. It
constitutes the 80 percent of Earth’s volume because of its
thickness of almost 2,900 kilometers. It has an upper mantle and
a lower mantle.
The asthenosphere, which lies below the lithosphere, is part of
the upper mantle. It is a layer of weak rocks which extends from
about 100 to 350 kilometers deep.
The core is the innermost layer of the Earth. It is made up of
mostly iron and nickel.
12. Continental Drift Theory
It was proposed by Alfred Wegener at the beginning of the
20th century.
According to him, all the major continents formed one
supercontinent called Pangaea and started to drift away.
He called the Northern part Laurasia and the southern
part Gondwanaland.
Among his evidences, that continents drifted away are: the
same types of fossilized animals and plants found in South
America and Africa; the shape of the east coast of South
America fits the west coast of Africa like pieces in a jigsaw
puzzle; and the matching of rock formations and mountain
chains found in South America and Africa are identical.
13.
14. Sea-Floor Spreading
Geologist Harry Hess proposed the hypothesis of Sea-
Floor Spreading in the early 1960s.
According to him, basaltic magma from the mantle
rises to create new ocean floor at mid-ocean ridges.
The seafloor moves from the ridge towards the deep-
sea trenches where it is subducted a and reprocessed
back into the mantle. The studies of the Earth’s
Magnetism provided a test of the hypothesis of sea-
floor spreading.
15.
16. Tectonic Plate
Tectonic Plate is a geological theory that was
developed during the late 1960s and has been
accepted and believed by most of the scientists
studying the Earth’s surface.
This theory is a product of two separate observations:
the Continental Drift during the 20th century and the
Seafloor Spreading in 1960s.
According to this theory, the Earth’s crust is broken up
into plates which are made of pieces of the Earth’s
lithosphere.
17.
18. The rates by which tectonic plates move vary
from less than 1 to 16 centimeters per year.
The continents and oceans move across the
surface of the Earth at the same rates by
which the plates move.
For instance, as the Mid-Atlantic Ridge
continues to move, North America at present is
drifting away from Europe at about 2.5
centimeters per year. This would mean that 20
years from now, North America will be 50
centimeters farther from Europe.
19. PLATE BOUNDARIES
A plate boundary is the point at which two
tectonic plates meet.
At this locations, tectonic activity results in
earthquakes, volcanic eruptions, and
formation of mountain ranges.
The various movements of plates relative to
others in a boundary account for the
variations in processes and landforms along
plate boundaries.
21. Convergent boundary
A convergent boundary is caused by the meeting of
plates from opposite directions resulting to one plate
to move beneath the other.
This process of sinking of plates beneath another
plate is called subduction.
The convergence of plates may occur in three ways.
It may happen between a continental crust and
oceanic crust, between two oceanic crust, and
between two continental crusts.
22.
23. Divergent boundary
A divergent boundary is a result of two plates
which are near each other moving in opposite
directions.
Divergence of plates may occur between two
oceanic crusts and between two continental
crusts resulting to the formation of mid-
oceanic ridges and rift valleys respectively.
24.
25. Transforming or sliding
boundary
A transforming or sliding boundary is the area
where two plates slide past each other as they
move in opposite directions.
This type of boundary can occur between two
oceanic plates and between two continental
crusts causing deformation of rocks and
earthquakes.
