Komatiites

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Komatiites

by massi2884 » Wed Jan 04, 2012 9:10 am
First identified in 1969, komatiites
are Earth's oldest known volcanic
rocks and contain three times as much
magnesium as do most volcanic rocks.
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
lava so that unusually high temperatures
would be required for the lava
to exist as a liquid.
Komatiites' discovery was surprising
in light of then-current geological
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
over whether or not the very high temperatures needed to produce magmas
rich in magnesium could have existed
on Earth. Hess suggested that the
presence of water, probably released
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
high temperatures were indeed necessary.
By 1960, it was generally
accepted that volcanic rocks with such
high levels of magnesium could not
exist, and thus the discovery of koma-
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.

Which of the following most accurately describes the organization of the passage?

A Two divergent views of a scientific phenomenon are reconciled.
B A phenomenon is described and its scientific significance is discussed.
C The discovery of a scientific phenomenon is traced and its implications for further research are suggested.
D A long-standing scientific theory is examined and recently discovered evidence is shown to support it.
E The ways in which a particular geological phenomenon is exceptional are detailed and classified. answer options b, I chose c, c does not see it from where

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by rijul007 » Wed Jan 04, 2012 10:35 am
IMO B
Whats the answer?

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by LalaB » Wed Jan 04, 2012 10:42 am
B is correct,since it was stated above-
"and thus the discovery of koma-
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. "

choice B -A phenomenon is described (the discovery of komatiites) and its scientific significance is discussed(changed geologists' assumptions about the characteristics of the Earth's mantle).

C is not correct , since no further research is described in a passage. u seem to have mistaken "further research" for Bowen's and Hess's discovery. in fact, their discovery (before 1960) was prior to the discovery of Komatiites (was found in 1969)

hope it helps

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by rijul007 » Wed Jan 04, 2012 11:14 am
The structure of this passage is like this

First para:
Rock K, discovered in 1969, has high concentration of Magnesium.

Second para:
This para discusses about some theories prior to 1969 that dismantled the existence of such kind of rocks.

Third para:
Discovery of rock K proved all those old assumptions wrong.

Now using process of elimination

Which of the following most accurately describes the organization of the passage?

A Two divergent views of a scientific phenomenon are reconciled. There are no two views
B A phenomenon is described and its scientific significance is discussed.
C The discovery of a scientific phenomenon is traced and its implications for further research are suggested. No future research work is mentioned in the passage
D A long-standing scientific theory is examined and recently discovered evidence is shown to support it. Wrong
E The ways in which a particular geological phenomenon is exceptional are detailed and classified. The passage doesn't mention anything exceptional.


Option B

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by massi2884 » Thu Jan 05, 2012 1:53 am
Thanks for the explanation. OA is B

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by santhoshsram » Fri Jan 06, 2012 2:43 pm
I agree B is the answer. Elimination worked for me. B comes closest.

However, is "discovery of something" a "phenomenon"? Not very sure. Please comment.
-- Santhosh S