Earth's Structure and Plate Tectonics

Comprehensive review flashcards covering Earth's internal structure, Alfred Wegner's Continental Drift hypothesis, supporting fossil and geological evidence, modern evidence for Plate Tectonics, and plate boundary mechanisms.

According to the lecture notes, what three factors heated the Earth when it initially formed as a molten mass?

The repeated impact of objects, the incorporation of decaying radioactive material, and gravitational pressure.

How did the Earth become internally layered during its cooling process?

Materials separated based on differing densities, where denser materials sank while less dense materials rose.

What is the primary composition and thickness of the continental crust?

It is primarily granitic rock and is $25\text{--}40\text{ mi}$ thick.

What is the primary composition and thickness of the oceanic crust?

It is primarily basaltic rock and is $< 5\text{ mi}$ thick.

What components make up the lithosphere?

The crust and the solid uppermost mantle, which act as a unit.

What are the physical characteristics of the asthenosphere?

It is the underlying area of the mantle that is hotter, under higher pressure, and plastic.

What hypothesis did Alfred Wegner propose in the early 1900's?

He proposed that all continents once existed as a single "super continent" called Pangea, which rifted into continental blocks that slowly drifted away to their current locations.

Approximately when did Pangea begin to break apart?

About $200\text{ mya}$.

What were the four independent lines of evidence used to support the Theory of Continental Drift?

1. The way some continents fit together; 2. Paleoclimatic evidence; 3. Similarities in rocks and mountains in different areas; 4. Similarities in fossils from different areas.

Which four fossil organisms provided evidence of matching ranges across separated continents?

Cynognathus, Lystrosaurus, Glossopteris, and Mesosaurus.

Which mountain systems and orogenies are noted as matching across separated continents?

The Caledonian Orogeny, Appalachians, Atlas, and Cape Fold.

What four additional lines of evidence contributed to the development of the Theory of Plate Tectonics?

1. The age of seafloor rocks in different locations; 2. Volcanic hot spots and the ages of volcanic islands; 3. Paleomagnetism and Polar Wandering; 4. Observance of plate motion using new technologies like G.P.S.

How does the age of seafloor rocks vary with distance from oceanic ridges?

Oceanic crust is new/young near oceanic ridges and increases in age away from them in both directions.

How was the Hawaiian Island chain produced according to hot spot evidence?

A large body of magma (a hot spot) penetrated the crust as the Pacific Plate moved northwest over it.

How does paleomagnetism provide evidence for seafloor spreading at oceanic ridges?

As Earth's magnetic field periodically flips, cooling igneous rocks record normal and reverse polarity, forming mirrored bands on either side of an oceanic ridge.

Which specific modern technologies are used to measure plate motion with high accuracy?

G.P.S. and Very Long Baseline Interferometery.

What two mechanisms drive overall plate motion?

Convection within the mantle and the sinking (subduction) of relatively old and dense oceanic crust.

What are the three types of plate boundaries and how do plates move at each?

Divergent plate boundaries (plates move away from each other and create new crust), convergent plate boundaries (plates move toward each other and collide), and transform plate boundaries (plates slide past each other laterally).