Download NOTES Plate Tectonics

The Theory of Plate Tectonics
The Theory of Plate Tectonics combines what geologists know about sea floor
spreading and continental drift into one theory. It states that the Earth is divided into
pieces of the lithosphere, called plates and these are in constant motion, driven by
convection currents in the asthenosphere.
1. Seismic Waves - Geologists study how these travel through the Earth to determine
what the Earth’s interior is made of.
2. The Earth is made of three main layers, the crust, mantle, and core.
A. Crust:
a. Oceanic crust is made up of mostly basalt.
b. Continental crust is made up of mostly granite.
B. Mantle:
a. Lithosphere - the crust and uppermost part of the mantle.
b. Asthenosphere - part of the mantle that can “flow.” The mantle is
2900 km thick.
C. Core:
a. The Earth’s core consists of the outer core which is molten and the
inner core which is solid.
b. The core is made up of iron and nickel.
3. Convection -- heat transfer by the movement of heated fluid. Heated particles rise
and cooled particles sink due to differences in density. (show earthgude
animation)
4. Describe how convection currents work in the Earth’s mantle:
Hot material near the core expands (density decreases) so it rises. As it
rises, it cools, density increases and it sinks back down.
vv
5. List the evidence Wegener found for his theory of continental drift:
a. Shape of continents
b. Similar mountain ranges, similar glacial deposits.
c. Fossils (ex. Glossopteris)
(show continental drift ppt)
6. Mid-Ocean Ridge - the longest mountain chain in the world. Scientists use SONAR
to map the ocean floor. (show earthguide animation)
7. What happens at the mid-ocean ridge?
New sea floor is made and spreads out.
8. List the evidence for sea floor spreading:
a. Magnetic “stripes” of reversals and normal polarity. (show earthguide
animation)
b. Young rocks close to the spreading center, progressively older rocks
away from the spreading center.
c. Submersibles – see magma coming out of the sea floor.
9. Where would you find the youngest rocks on the sea floor? At a mid-ocean ridge –
spreading center.
10. If new ocean floor is added all the time at mid-ocean ridges, why is the Earth not
getting larger?
Old ocean floor is subducted at continental margins.
11. Subduction - the process that occurs when ocean floor sinks beneath a deep
ocean trench and returns to the mantle.
12. The Pacific Ocean is shrinking and the Atlantic Ocean is expanding.
13. The three kinds of plate boundaries are:
a. Transform - where two plates slip past each other in opposite directions.
b. Divergent - where two plates move apart (mid-ocean ridge).
c. Convergent - where two plates come together. The plate that is most dense
will sink below the other plate. Oceanic crust is more dense than
continental crust.