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1. What is the Geologic Time Scale based on?
2. What 2 events characterize the Cenozoic Era?
3. What 2 events characterize the Quaternary
Period?
4. What are the two types of crust and how are
they different?
5. Describe the consistency of the upper
portions of Earth’s mantle
Unit 1- Earth Systems and
Resources
Plate Tectonics
AIM: What are tectonic plates and how
have they moved over time?
Lithosphere
• The solid, outer part of Earth
• Consists of the crust, and the uppermost
mantle
Asthenosphere
• Upper portion of the mantle that has a
“plastic-like” consistency
Asthenosphere – “plastic like”
Lithosphere – Solid
• Earth’s lithosphere is divided into several large
pieces called “tectonic plates”
• The plates are constantly moving, a phenomena
known as “plate tectonics”
– 2-5 cm a year
• The plates (lithosphere) are able to glide on the
plastic-like portion of the mantle, known as the
asthenosphere
• The lithosphere glides on the asthenosphere
• Slow creeping motion of the mantle is caused by
convection currents, carrying heat from Earth’s
interior to the surface
Convection currents in the asthenosphere move
plates in the lithosphere
Theory of Plate Tectonics..
• The theory of plate tectonics arose out of 2
separation geological observations:
– The continental drift theory
– The seafloor spreading theory
Continental Drift
• Alfred Wegner proposed that all present-day
continents originally form one land-mass- Pangaea
• Wegner proposed that this supercontinent began to
break up 200 million years ago
1. Fossilized tropical plants were found in
Greendland’s icecaps
2. Tropical regions on some continents had polar
climates in the past
3. The continents fit together like puzzle pieces
4. Similarities existed in rocks between the east coast
of North and South America and the west coasts of
Africa and Europe
5. Fossils of extinct land animals were found on
separated land masses
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Tropical plants fossils in cold climates
Continents fit like a puzzle
Coasts of different continents have same rocks
Fossils of extinct species found on separated
landmasses
Plate Tectonics
• Earth’s lithosphere is divided into 8 major plates
• Divisions between plates are called boundaries
Plates interact at their boundaries
• There are 3 types of plate boundaries
– Transform boundaries
– Divergent boundaries
– Convergent boundaries
Transform Boundaries
• Two plates slide past each other
Divergent Boundaries
• Two plates slide apart from each other
Convergent Boundaries
• Two plates slide towards each other
• If an oceanic plate and a continental plate are
colliding, the oceanic plate will slide under the
continental plate
– The oceanic plate is more dense
– This is called SUBDUCTION