自然学科是托福阅读文章题材中比较常见的类型，本系列为大家汇总整理了多篇托福阅读自然科学类文章，大家在托福备考时可以有针对性的进行复习，前程百利小编为大家带来的是托福阅读自然科学话题 Crust and the Upper Mantle，并附有相应的练习，希望大家都能顺利拿下托福阅读高分。
Crust and the Upper Mantle
Keywords:plates, Earth's crust, upper mantle, The rocks of the crust, rigid layer, tectonics, earthquakes, volcanoes, geologists
The hard, rigid plates that form the outermost portion of the Earth are about 100 kilometers thick. These plates include both the Earth's crust and the upper mantle.
The rocks of the crust are composed mostly of minerals with light elements, like aluminum and sodium, while the mantle contains some heavier elements, like iron and magnesium. Together, the crust and upper mantle that form the surface plates are called the lithosphere. This rigid layer floats on the denser material of the lower mantle the way a wooden raft floats on a pond. The plates are supported by a weak, plastic layer of the lower mantle called the asthenosphere. Also like a raft on a pond, the lithospheric plates are carried along by slow currents in this more fluid layer beneath them.
With an understanding of plate tectonics, geologists have put together a new history for the Earth's surface. About 200 million years ago, the plates at the Earth's surface formed a "supercontinent" called Pangaea. When this supercontinent started to tear apart because of plate movement, Pangaea first broke into two large continental masses with a newly formed sea that grew between the land areas as the depression filled with water. The southern one-which included the modern continents of South America, Africa, Australia, and Antarctica-is called Gondwanaland. The northern one-with North America, Europe, and Asia-is called Laurasia. North America tore away from Europe about 180 million years ago, forming the northern Atlantic Ocean.
Some of the lithospheric plates carry ocean floor and others carry land masses or a combination of the two types. The movement of the lithospheric plates is responsible for earthquakes, volcanoes, and the Earth's largest mountain ranges. Current understanding of the interaction between different plates explains why these occur where they do. For example, the edge of the Pacific Ocean has been called the "Ring of Fire" because so many volcanic eruptions and earthquakes happen there. Before the 1960's, geologists could not explain why active volcanoes and strong earthquakes were concentrated in that region. The theory of plate tectonics gave them an answer.
1. With which of the following topics is the passage mainly concerned?
(A) The contributions of the theory of plate tectonics to geological knowledge
(B) The mineral composition of the Earth's crust
(C) The location of the Earth's major plates
(D) The methods used by scientists to measure plate movement
2. According to the passage, the lithospheric plates are given support by the
(A) upper mantle
(B) ocean floor
(C) crust
(D) asthenosphere
3. The author compares the relationship between the lithosphere and the asthenosphere to which of the following?(A) Lava flowing from a volcano
(B) A boat floating on the water
(C) A fish swimming in a pond
(D) The erosion of rocks by running water
4. The word "one" in line 16 refers to
(A) movements
(B) masses
(C) sea
(D) depression
5. According to the passage, the northern Atlantic Ocean was formed when
(A) Pangaea was created
(B) plate movement ceased
(C) Gondwanaland collided with Pangaea
(D) parts of Laurasia separated from each other
6. The word "carry" in line 20 could best be replaced by
(A) damage
(B) squeeze
(C) connect
(D) support
7. In line 27, the word "concentrated" is closest in meaning to which of the following?
(A) Allowed
(B) Clustered
(C) Exploded
(D) Strengthened
8. Which of the following can be inferred about the theory of plate tectonics?
(A) It is no longer of great interest to geologists.
(B) It was first proposed in the 1960's.
(C) It fails to explain why earthquakes occur.
(D) It refutes the theory of the existence of a supercontinent.
9. The paragraph following the passage most probably discusses
(A) why certain geological events happen where they do
(B) how geological occurrences have changed over the years
(C) the most unusual geological developments in the Earth's history
(D) the latest innovations in geological measurement
参考答案：AABBD DBBB
以上就是为大家整理的托福阅读自然科学类文章之The Earth's Crust and the Upper Mantle，希望能够帮助大家备考。祝大家都能取得理想的托福考试成绩。
