[单项选择]

Continental Drift

Continental drift, and the subsequent theory of plate tectonics, forms the modern framework for geological study of the Earth. Continental drift stems from scientific notions as early as the 16th century that the Earth’s continents were once a single land mass, which scientists have termed Pangaea, meaning "all lands" in Greek. In 1912, German meteorologist Alfred Wegener proposed that natural forces such as earthquakes and floods broke Pangaea apart between 225 and 200 million years ago, and it eventually fragmented into the continents as we know them today. Wegener based his theory on four major observations: first, the amazing fit of the African and South American continents; second, the similarities of unusually structured plant and animal fossils discovered along the coastlines of South America and Africa, even though they are separated by the Atlantic Ocean; third, similarities in rocks and ice sheets on these two
A. tracked.
B. finished.
C. perturbed.
D. angere

[单项选择]
Continental drift, and the subsequent theory of plate tectonics, forms the modern framework for geological study of the Earth. Continental drift stems from scientific notions as early as the 16th century that the Earth’s continents were once a single land mass, which scientists have termed Pangaea, meaning "all lands" in Greek. In 1912, German meteorologist Alfred Wegener proposed that natural forces such as earthquakes and floods broke Pangaea apart between 225 and 200 million years ago, and it eventually fragmented into the continents as we know them today. Wegener based his theory on four major observations: first, the amazing fit of the African and South American continents; second, the similarities of unusually structured plant and animal fossils discovered along the coastlines of South America and Africa, even though they are separated by the Atlantic Ocean; third, similarities in rocks and ice sheets on these two
A. opposition of climates.
B. fit of continents.
C. similarities of living animals.
D. similarities in rocks and ic

[简答题]

The Theory of Continental Drift has had a long and turbulent history since it was first proposed by Alfred Wegener in 1910. (46) Vigorously challenged yet widely ignored, the theory had languished for half a century, primarily due to its lack of a plausible mechanism to support the proposed drift. With the discovery of sea-floor spreading in the late 1950’s and early 60’s, the idea was reinvigorated. Plate tectonics is now almost universally accepted. Many details of the mechanism are to be worked out.
The surface of the Earth is divided into approximately six large plates, plus a number of smaller ones. The plates are’ bounded by an interconnected network of ridges, transform faults, and trenches. Ridges, also called spreading centers, occur where two plates are moving away from each Other. As the plates separate, hot molten mantle material flows up to fill the void. (47) The increased heat resulting from this flow reduces the density of the p