问题详情:
Most of the time, the ground feels solid beneath our feet. That's
comforting. But it's also misleading because there's actually a lot going on
underground. Masses of land (called plates) slip, slide, and bump against each
other, slowly changing the shape of continents and oceans over millions and
billions of years.
Scientists know that Earth formed about 4. 5 billion years ago. They also
know that our planet was hot at first. As it cooled, its outermost layer, called
the crust (地壳), eventually formed moving plates. Exactly when this shift
happened, however, is an open question.
Now, an international group of researchers has an answer. They've found
new evidence suggesting that Earth's crust started shifting at least 3.8 billion
years ago. The new estimate is l. 3 billion years earlier than previous ones.
Not long before 3. 8 billion years ago, lots of small planets were hitting
Earth, keeping its crust in a hot, melting state. After the hard crust formed,
much of it sank at various times into the planet's hot insides. There, it melted
before returning to the surface.
In some places, however, the crust never sank. One of the oldest such places
is in Greenland, in an area called the Isua supracrustal (上地壳) belt. The rocky
crust there is between 3. 7 and 3. 8 billion years old. The belt was once part of the
seafloor, but now it is exposed to air.
The researchers recently took a close look at the Isua supracrustal belt. They
noticed long, parallel cracks(裂缝)in the rock that have been filled in with a
type of volcanic rock.
To explain this structure, the scientists propose that tension in the crust
caused the seafloor to crack open long ago. Hot, liquid rock oozed from deep
inside Earth to fill the cracks. Finally, the whole area cooled, forming what we
see today.
That explanation, plus chemical clues inside the rock, suggests that the Isua
supracrustal belt was once part of plate under the ocean, beginning around 3.8
billion years ago.
“It's a fantastic case of solving a jigsaw puzzle(拼图),”says one of the
researchers. He notes that the puzzle was “a very difficult one because these
rocks are all very old and have been badly ruined".
32. The underlined phrase “oozed from" in Paragraph 7 is closest in meaning to
A. filled up gradually
B. washed away quickly
C. flew out of slowly
D. broke through suddenly
33. What can we infer from the text?
A. The shapes of continents and oceans changed slowly.
B. The Earth's crust started shifting l.3 billion years ago.
C. The crust began to shift when the Earth was hot.
D. The hit from small planets made the Earth cool.
34. What do scientists know about the past of the Isua supracrustal belt?
A. It was once covered by hot, liquid rock.
B. It remained under the deep sea.
C. It stayed hot and sinking.
D. It kept moving slowly.
35. The text is mainly about
A. why the Earth cooled
B. how the Isua supracrustal belt formed
C. whether the ground beneath our feet is still
D. when Earth's crust began shifting
【回答】
CABD
知识点:科普环保类阅读
题型:阅读理解