Scattered around the globe are more than 100 smallregions of isolated volcanic activity known togeologists as hot spots. Unlike most of the world'svolcanoes. they are not always found at theboundaries of the great drifting plates that make upthe earth's surface; on the contrary, many of chemlie deep in the interior of a plate. Most of the hot spots move only slowly, and in some cases themovement of the plates past them has left trails of dead volcanoes. The bot spots and theirvolcanic trails are milestones that mark the passage of the plates.

That the plates are moving is now beyond dispute. Africa and South America. for example. aremoving away from each other as new material is injected into the sea floor between them. Thecomplementary coastlines and certain geological features that seem to span the ocean arereminders of where the two continents were once joined. The relative motion of the platescarrying these continents has been constructed in detail, but the motion of one plate withrespect to another cannot readily be translated into motion with respect to the earth’s interior. It is not possible to determine whether both continents are moving in opposite directions orwhether one continent is stationary and the other is drifting away from it. Hot spots. anchoredin the deeper layers of the earth, provide the measuring instruments needed to resolve thequestion. From an analysis of the hot-spot population it appears that the African plate isstationary and that it has not moved during the past 30 million years.

The significance of hot spots is not confined lo their role as a frame of reference. It nowappears that they also have an important influence on the geophysical processes chat propelthe plates across the globe. When a continental plate comes to rest over a hot spot. thematerial rising from deeper layer creates a broad dome. As the dome grows, it develops deepfissures (cracks); in at least a few cases the continent may break entirely along some of thesefissures, so that the hoc spot initiates the formation of a new ocean. Thus just as earliertheories have explained the mobility of the continents, so hot spots may explain theirmutability (inconstancy).

1.We can learn from che first paragraphthat_____________.

A. there are no volcanic activities on hoc spots

B. most hoc spots are located in the inner part of aplate

C. hot spots usually lie. at che boundaries of drifting plates;

D. the passage of plates through hot spots will leave dead volcanoes

2.The author believes that_____________.

A) the motion of the plates corresponds to thar of the earth's interior

B) the geological theory about drifting plates has been proved to be true

C) the hot spots and the plates move slowly in opposite directions

D) the movement of hot spots proves the continents are moving apart

3.That Africa and South America were once joined can be deduced from the factthat_________.四级考试多长时间

A) the two continents are still moving in opposite directions

B) they have been found to share certain geological features

C) the African plate has been stable for 30 million years

D) over 100 hot spots are scattered all around the globe

4.The hot spot theory may prove useful in explaining__________.

A) the structure of the African plates.

B) the revival of dead volcanoes.

C) the mobility of the continents.

D) the formation of new oceans.