Plate Tectonics

1. How have geologists learned about Earth's inner structure?
They use evidence from rock samples, which allow scientists to make inferences about where the rocks were formed and the conditions deep inside Earth. Geologists also have evidence from seismic waves. They record these waves and study how they travel through Earth.

2. How is Earth's interior like an apple?
It's like an apple because the crust is the skin, the mantle is like the meat, and the core is like the core of the apple.

3. What are the layers of Earth?
The layers of Earth are the crust, the mantle, the outer core, and finally the inner core.

4. What are the characteristics of Earth's crust, mantle, and core?
The crust is 5-70 km thick and is made up of oceanic and continental crust. The mantle is 2,867 km thick and is made up of three layers: the lithosphere (solid rock), the asthenosphere (soft rock), and the lower mantle (solid rock). The outer core is a layer of molten metal, and is 2,266 km thick. The inner core is 1,216 km thick and is a dense ball of solid iron and nickel.

5. How is heat transferred?
It is transferred in three ways: radiation, conduction, and convection. Radiation is the transfer of heat through space, like an open fire. Conduction is heat transfer within a material or between materials that are touching. It is a lot like walking on hot sand on the beach because the heat from the sand is transferred to your feet. Convection is heat transfer by the movement of currents in a fluid, much like heating up water on a stove.

6. What causes convection currents?
A convection current is the flow that transfers heat within a fluid, and it is caused by heating and cooling of the fluid, changes in the fluid's density, and gravity.

7. What causes convection currents in the mantle?
It is caused heat from the core and the heat from the mantle itself.

8. What was Alfred Wegener's hypothesis about the continents?
His hypothesis was that all the continents were once joined together in a single landmass called Pangaea and have since drifted apart.

9. What evidence supported Wegener's hypothesis?
Evidence from land features such as the fact that mountain ranges along the coast of South America and Africa line up very nicely supported it. Evidence from fossils such as the same animal's fossils found in different continents also supports it. There's no way those animals could have swam an ocean. Finally, evidence from climate supports the hypothesis because some very cold areas have tropical plant fossils on them. The area must have previously been a tropical area and moved away.

10. Why was Wegener's hypothesis rejected by most scientists of his time?
Wegener couldn't produce an explanation for what pushed or pulled the continents to their current positions.

11. How does sea-floor spreading provide a way for continents to move?
In sea-floor spreading, new material is continuously added to the ocean floor. That turns the ocean floors into conveyor belts, and those conveyor belts carry with them the continents.

12. What is the evidence for sea-floor spreading?
Evidence from molten material supports the theory because scientists found rocks in a mid-ocean ridge that can only be formed by the hardening of molten material. Evidence from magnetic stripes supports it because stripes were found on the ocean floor that are rocks formed from the Earth's magnetic field. Finally, evidence from drilling samples supports it because samples of rock were taken from a mid-ocean ridge. The closer the rocks were to the ridge, the younger they were.

13. What happens at deep-ocean trenches and why?
Subduction, the process by which the ocean floor sinks back into the mantle, occurs at deep-ocean trenches. That happens because new crust pushes old crust down into the mantle.

14. What is the Mid-Atlantic Ridge?
It is a very long, very big mid-ocean ridge that stretches for almost the whole entire Atlantic Ocean.

15. What is the theory of plate tectonics?
It states that pieces of Earth's lithosphere are in slow, constant motion, driven by convection currents in the mantle.

16. What are the three types of plate boundaries and what are their characteristics?
First there is divergent boundaries, which is the place where two plates move apart, or diverge. This occurs mostly along mid-ocean ridges, and form rift valley which is the space between the two plates. Second there is convergent boundaries, which is the place where two plates come together. Density plays a role in which plate will sink down into the mantle. The last are transform boundaries, which is a place where two plates slip past each other, moving in opposite directions. Earthquakes occur when this happens.