GWD 30-12,13

1.        GWD-30-Q11-Q13 最老的火山岩石和发现它的科学意义

      First identified in 1969, komatiites

       are Earth’s oldest known volcanic

       rocks and contain three times as much

Line       magnesium as do most volcanic rocks.

  (5)      This chemical composition suggests

that komatiites formed from the hottest

lava known ever to have erupted:  a

high concentration of magnesium

changes the physical properties of

 (10)      lava so that unusually high tempera-

tures would be required for the lava

to exist as a liquid.

      Komatiites’ discovery was surpris-

ing in light of then-current geological

 (15)       theories about magmas, molten rock

that forms in the Earth’s mantle (the

layer beneath the crust) and composes

volcanic lava eruptions.  Prior to 1960,

geologists Bowen and Hess disagreed

 (20)      over whether or not the very high tem-

       peratures needed to produce magmas

       rich in magnesium could have existed

on Earth.  Hess suggested that the

presence of water, probably released

 (25)      from minerals decomposing in the

Earth’s mantle, might have meant that

a high-magnesium magma could have

existed at a lower temperature.  But

Bowen showed experimentally that the

 (30)      high temperatures were indeed nec-

essary.  By 1960, it was generally

accepted that volcanic rocks with such

       high levels of magnesium could not

exist, and thus the discovery of koma-

 (35)
                       tiites changed geologists’ assumptions

about the characteristics of the Earth’s

mantle around the time of the formation

of komatiites, between 2.5 and 4 billion

      years ago.

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Q13:

Which of the following most accurately states the main point of the passage?

1. Komatiites provide information about rates of volcanic eruption between 2.5 and 4 billion years ago.
2. Komatiites provide information about how the physical properties of lava in the Earth’s past compare with those of current-day lava.
3. Komatiites provide evidence that undermines Bowen’s experimental conclusions regarding the temperatures at which lava exists as a liquid.
4. Komatiites provide evidence that has changed geologists’ ideas about the characteristics of the Earth’s mantle between 2.5 and 4 billion years ago.

5. Komatiites provide evidence that water in the Earth’s mantle may have reduced the temperature required for lava to exist as a liquid.

这两题怎么选出来的阿，看了N久没看明白，虽然觉得这两个最相关的，但是总觉得不对；

“By 1960, it was generally accepted that volcanic rocks with such high levels of magnesium could not exist, ”

关键这句话没看明白，为啥 could not exist，komatiites不就是high levels of magnesium 吗

请各位帮忙解答下阿!!!

顶一下

Q12:

Information in the passage suggests which of the following concerning the Earth’s mantle 2.5 to 4 billion years ago?

1. It contained magmas that were more significantly affected by the decomposition of minerals than are current-day magmas.无关

2. It contained a lower proportion of water that it contains today.无关

3. Its characteristics were accurately described by both Bowen and Hess. 无关

4. Its temperature was sufficiently high to produce magmas with high magnesium content.

双重否定，原文的改写，以前认为不存在，现在，这个地理现象的发现导致了人们观点的改变，即存在了：volcanic rocks with such high levels of magnesium

5. Its total magnesium content then was roughly equivalent to its magnesium content today.无关，不知道today的情况。

By 1960, it was generally

accepted that volcanic rocks with such

         high levels of magnesium could not

exist, and thus the discovery of koma-

 (35)
                   tiites changed geologists’ assumptions

about the characteristics of the Earth’s

mantle around the time of the formation

of komatiites, between 2.5 and 4 billion

         years ago.

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Q13:

Which of the following most accurately states the main point of the passage?

1. Komatiites provide information about rates of volcanic eruption between 2.5 and 4 billion years ago.

2. Komatiites provide information about how the physical properties of lava in the Earth’s past compare with those of current-day lava.

3. Komatiites provide evidence that undermines Bowen’s experimental conclusions regarding the temperatures at which lava exists as a liquid.细节

4. Komatiites provide evidence that has changed geologists’ ideas about the characteristics of the Earth’s mantle between 2.5 and 4 billion years ago.原文的改写

5. Komatiites provide evidence that water in the Earth’s mantle may have reduced the temperature required for lava to exist as a liquid.细节