Transcript The Changing Earth

The Changing Earth
Plate Tectonics
Earth Has Several Layers
Earth’s layers have different
properties.
Earth’s Layers
Layer
Composition
Temperature
Thickness
Inner Core
solid metals
7000-8000°C 2400 km
diameter
Outer Core
liquid metals
4400-6100 °C 2300 km
thick
Mantle
heated rock
870-4400 °C
2900 km
thick
Crust
Cooler rock
0-700 °C
6-70 km thick
Continued
 Earth’s crust and the top of the
mantle form the lithosphere.
The lithosphere is made up of
many plates.
Continued
 The lithosphere is split into large and
small slabs of rocks called tectonic
plates, which fit together like a jigsaw
puzzle.
 Most large plates contain both continental
and oceanic crust.
Continents Change
Position Over Time.
Continents join together
and split apart.
 Alfred Wegener proposed the theory
of continental drift in early 1900’s
 All continents were once joined and
gradually moved apart (still moving).
 Fossils, studies of ancient climates, and
rock formations provide evidence.
 Africa and Brazil have matching rock
formations indicating they were once joined.
Plates Move Apart
Wegner used fossil evidence to support
his continental drift theory.
Continued: Sea Floor Spreading
The sea floor spreads apart at
divergent boundaries.
 Sea floor spreading occurs at
divergent boundaries in the ocean.
Continued
 Old crust gets pushed aside and the
sea floor slowly spreads apart.
 Earth DOESN’T get larger because
oceanic crust is destroyed along
deep-ocean trenches, where the
oceanic plates sink.
Tectonic plates have different
boundaries.
 Plate boundary: where the edges of
two plates meet
 Divergent Boundary: occurs where plates
move apart, usually found in the ocean
 Convergent Boundary: occurs when plates
push together.
 Transform Boundary: occur when plates
scrape past each other.
Divergent Boundary
Convergent Boundary
Transform Boundary
Continents split apart at
divergent boundaries.
 Divergent boundaries on continents
produce rift valleys.
 Magma rises through cracks and forms
volcanoes.
Hot spots can be used to track
plate movements.
 Hot Spot: an area of volcanic activity
that develops above where magma
rises in a plume from the mantle.
 Can be used to measure plate movement
because it generally stays in one place as
the tectonic plate above it moves.
 Can provide a fixed point for measuring
the speed and direction of plate
movements.
The Hawaiian islands are located in the middle
of the Pacific Plate. The largest island, Hawaii,
is still over the hot spot.
When the plate moves on, it carries the first volcano away
from the hot spot. Heat from the mantle plume will then
melt the rock at a new site, forming a new volcano.
Plates
Converge or
Scrape
Past Each
Other.
See Page 32
Tectonic plates scrape past each
other at transform boundaries.
 Two plates move
past each other in
opposite directions.
 No crust is formed
or destroyed.
 Occurs on the sea
floor and on land.
The San Andreas Fault is a transform
boundary and moves about 1 inch per year.
See Page 35
Boundaries are
formed when
tectonic plates
move. The
direction of the
movement
determines the
type of
boundary.
The theory of plate tectonics
helps geologists today.
 The plate tectonics
theory enables
geologists to
understand how
Earth’s continents and
ocean basins formed.
 Helps scientists
predict earthquakes
and volcanic activity.