Download Continental drift - La Salle Elementary School

Dynamic Earth
Chapter 3
Plate Tectonics Highlights
A. Highlights for Section 1 pages 55-59
 Alfred Wegener (German scientist) proposed a
theory:
o Continental drift
 Earth was once a single landmass called
Pangaea that has since broken up into
large pieces that drifted apart.
 Evidence from fossils – preserved remains of
ancient organisms support theory
o Identical types of fossils found in Africa and
South America
o Only explanation – places where fossils
found must have been closer
 More evidence found in rock formations in
Africa match ones in South America
 Glacial deposits are similar in Africa, South
America, India, Australia, and Antarctica were
left by same ice sheets.
F. Highlights for Section 2 pages 60-64
 Large systems of underwater mountains that have a
deep crack are called a rift valley running through the
center – mid ocean ridges.
o Lava erupts from rift valley
o Ocean floor moves away on either side of the ridge
– lava wells up and hardens
o Hardened lava forms a new ocean floor – ocean
floor spreading
 Ocean floor spreading explains how continents
drift
 As ocean floor moves, it takes continents with
it
 Straight ridge sections are offset by thin cracks knows
as transformation faults.
o Earthquakes occur along the faults
 Rock samples from ocean floor indicate rocks next to
midocean ridge are younger rocks than farther away.
o Ocean floor spreads – older rocks move farther
from ridge
 Deepest parts of ocean are V-shaped valleys called
trenches.
o Older ocean floor moves down deep into earth
along trenches – called subduction.
o As new rocks form – older rocks subducted into
trenches
o One process balances the other – crust remains
same size
O. Highlights for Section 3 pages 64-71
 Evolution of Earth can be explained with Theory of Plate Tectonics.
o Plates are moving – irregularly shaped slabs – fit together like
paving stones
 Carry continents and are edged by trenches and ridges
o Tectonics – branch of geology that deals with movements that
shape Earth’s crust
 Links together ideas of continental drift and ocean floor
spreading
 According to theory – topmost solid part of Earth – Lithosphere – made
of a number of plates
o Plates contain thin layer of crust above a thick layer of cool rigid
mantle
 7 major lithospheric plates
 All move at different speeds and directions
 3 types of plate boundaries
o Midocean ridges
 Plates move apart at midocean ridges – divergent
boundaries
o Trenches
 Plates come together at trenches – convergent
boundaries. Collision of plates here cause earthquakes and
volcanoes.
o Transform fault
 These boundaries are called strike slip boundaries – 2
plates grind together and slip past each other horizontally.
Earthquakes are common along strike slip boundaries
 Scientists think that convection currents within the Earth may be what
makes plates move.
o Convection currents are created by circular motion of molten
material in mantle due to differences in its temperatures – motion
carries the plates of lithosphere with it.