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
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
