Alfred Wegener used evidence like matching coastlines and continental drift to develop his theory of continental drift. People did not initially believe it because he could not explain how the continents moved. Arthur Holmes and Harry Hess later provided supporting evidence including that continents are carried by tectonic plates. There are three types of plate boundaries: divergent where plates pull apart, convergent where they push together, and transform where they slide past each other. Plate tectonics causes earthquakes and volcanoes from the energy at plate boundaries, but also provides fertile soils, ore deposits, and fossil fuels that have benefited humans.

1. Plate Tectonics
By: Andrew Sanders

2. What evidence did Alfred Wagner use to support his theory of
continental drift?
• Alfred Wegener's fully developed theory of continental
drift attempted to point out evidences that the continents
were once joined into a single continent he called Pangea.
Ever since the continents were all mapped, people had
noticed that many coastlines, like those of South America
and Africa, looked as though they would fit together if
they could be moved like puzzle piece. He noticed that,
based on nineteenth-century longitude determinations, it
appeared that Greenland had moved a mile away from
Europe in a hundred years. And Paris and Washington,
D.C., seemed to be moving apart by about 15 feet each
year while San Diego and Shanghai got about six feet
closer.

3. Why do you think people didn't believe continental drift theory
when Wagner first explained it?
• Wegener could not come up with an acceptable
way to explain how the continents moved and this
caused speculation among the people.

4. Who were the two scientist that brought forth supporting evidence
to Wagner's theroy, and what was their evidence?
• Arthur Holmes and Harry Hess helped Wagners
theroy because Holmes suggested that the
continents didn't move but were "carried" by larger
pieces of the earth's crust. The controversy quieted
down and fell from prominence until the 1960s,
when new evidence was brought to the fore.
Discoveries of the Mid- Oceanic Ridge and the
work of Harry Hess and others led to the
development of plate tectonics. Though not without
problems, this theory has gained wide acceptance.

5. What are the three different types of plate boundaries, describe each
type?
• Divergent boundaries -- where new crust is
generated as the plates pull away from each other.
• Convergent boundaries -- where crust is destroyed
as one plate dives under another.
• Transform boundaries -- where crust is neither
produced nor destroyed as the plates slide
horizontally past each other.

6. Give an example on Earth where each type of plate boundary is
present.
Convergent
Divergent
Transform

7. What are the three different types of convergent plate boundaries?
• Oceanic-continental convergence
• Oceanic-oceanic convergence
• Continental-continental convergence

8. What types of tectonic forces create mountains?
• The type of tectonic forces that create mountains
are called converging plates. As two continental
plates push together, the stress forces them both
upwards. Because of this the Himalayas are still
growing.

9. • Graben are produced from parallel normal faults,
where the hanging wall is downthrown and the
footwall is upthrown. The faults typically dip
toward the center of the graben from both sides.
Horsts are parallel blocks that remain between
grabens, the bounding faults of a horst typically dip
away from the center line of the horst.

10. What are two bad things that can happen as a result of plate
tectonics, how did plate tectonics cause these events?
• Volcano eruptions and earthquakes. When plates
bump into each other, a source of energy is created
deep inside the earth called a focus.

11. What are three good things that plate tectonics provide for humans,
how do plate tectonics provide these things?
• fertile soils, ore deposits, and fossil fuels