Plate tectonics and continental drift

What is the main idea Alfred Wegener proposed in the

“Theory of Continental Drift” that he published in 1915?

• The continents were once a single landmass that drifted apart.

• The continents float on a liquid layer that allows them to move.

• The seafloor has spread the continents into separate landmasses.

• The fossils found on Earth are evidence of change over time.

What observation did Alfred Wegener make that led him to develop the theory of continental drift?

• Continents appear to have once fit together.

• The seafloor has “magnetic stripes”

• Earth’s magnetic poles have reversed polarity in geologic history.

• The ocean floor has long ridges of volcanic mountains.

How did Wegener explain rain-forest fossils that are now found in arid or cold regions of Earth?

• The land they are on was once closer to the equator.

• Heat from Earth’s interior made the climate warmer.

• Animals migrated from continent to continent.

• Earth was closer to the sun in ancient times.

How was Alfred Wegeners’ theory accepted in his time?

• reasonably well, some scientists questioned the rock types.

• not at all, there was not a way to explain the moving continents.

• poorly, most people thought the earthquake data was wrong.

• very well, scientists saw the fit of the continents..

How does Earth’s geologic record support the continental drift theory?

• Glacial erosion patterns on different continents match up.

• Sedimentary layers are always found in horizontal positions.

• Volcanic chains on one continent match those on other continents.

• Continents are all made from one type of rock.

How does the fossil record support the continental drift theory?

• Fossil plants and animals are found on all continents.

• Fossils of the same type are found on continents that were once together.

• Fossils can be dated through radioactive decay to show age of sediments.

• Fossils were formed in the same way and at the same time.

How does continental drift explain the pattern of Mesosaurus fossils?

• The Mesosaurs were found on the coast of every continent on Earth.

• Mesosaurs were marine animals that could swim the Atlantic Ocean.

• South American and African animals are all descendants of mesosaurs.

• South American and Africa were once part of the same continent.

How did the discovery of sea-floor ridges affect the ability of the scientific community to accept Alfred Wegener’s ideas?

• The ridges contained the oldest rocks on Earth.

• The ridges showed that earthquakes occur randomly.

• The ridges helped to explain plate movement.

• The ridges proved his theory was a law.

Scientists knew that Earth was not getting bigger as new crust was formed at the ridges. What did the discovery of oceanic trenches help scientists understand?

• That the crust was made of a plastic-like substance.

• That the crust was thicker in some places than in others.

• That the crust was made of 9 tectonic plates.

• That the crust could be created and destroyed.

What does the “striping” of the sea floor indicate about Earth?

• The rocks cooling from the magma have changed composition.

• The seafloor has an uneven surface.

• The magnetic pole has switched from north to south poles.

• The age of the rocks on the sea floor varies.