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Until recently, paleontologists assumed that the changes

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Until recently, paleontologists assumed that the changes [#permalink] New post 08 May 2005, 00:39
Until recently, paleontologists assumed that the changes that brought the Permian period to an end, roughly 250 million years ago, took place gradually. However, the precise dating of the period's end, just recently established, has cast doubt on this theory by enabling a worldwide comparison of geological evidence. Comparing rock formations, researchers discovered a nearly identical and instantaneous global sequence of events at the exact close of the Permian. Black mud deposits, formed in the absence of oxygen, appeared in place of red, green, or gray rocks laid down when oxygen is present. Simultaneously, a drastic change in the concentration of atmospheric gases occurred, as evidenced by a sudden shift in the isotope ratios of rock carbon. These events coincided with a cataclysmic mass extinction which destroyed roughly 90% of the earth's species.

While some contend that the mass extinction was caused by a meteorite, further studies do not bear this out. A more plausible theory concerns huge volcanic eruptions in Siberia. Recent lava dating has shown that these explosions occurred at the same time as the extinctions. Researchers speculate that carbon dioxide released in the blasts increased the greenhouse effect, causing an increase in global temperatures that destabilized methane hydrate, a superconcentrated frozen gas. The methane release accounts for the shift in carbon isotopes and further enhanced the greenhouse effect, resulting in runaway global warming that contributed to the extinction. Studies of changes in oxygen isotope ratios have estimated the warming to be 6 degrees Celsius. Atmospheric scientists contend that a similar rise is not impossible by 2100. These findings therefore reinforce the urgency of addressing the problem of global warming in our time.

Q. Which of the following best characterizes the process that resulted from the Siberian volcanic eruptions as that process is described in the second paragraph?


a. A random interaction
b. A self-defeating mechanism
c. A positive feedback loop
d. A negative feedback loop
e. A pre-determined sequence of events
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 [#permalink] New post 08 May 2005, 05:35
My AC is E.

Passage: Scientists dismiss old theory with a new theory further supported by the Siberian volcanic explosion.
Time: ~3.5 minutes. 2 to read and 1.5 to answer AC.

Question: What process resulted from the siberian volcanic eruptions.

The AC are definitely wierd in my opinion. I go with "E". Reason listed below.

A: "random" is definitely not the verbiage used to describe the process because of the "chain reaction" the volcano eruption starts up.
B: Totally wierdd AC. "Self-defeating"?? Where did that come from?
C: I dont like the AC's because of the verbiage "positive". Nothing in passage describe postive in the context of the passage.
D: I dont like the AC's because of the verbiage "negative". Ditto as C.
E: The Volcanic eruptions definitely triggered of a "chain reactions". Am not a 100% sure why the word predetermined is be used.

Any explain why? But my AC is E.
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 [#permalink] New post 10 May 2005, 07:33
Bumping up this thread...
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Re: RC: Extinction of the Dinosaurs (difficult) [#permalink] New post 10 May 2005, 12:32
GMATT73 wrote:
Researchers speculate that carbon dioxide released in the blasts increased the greenhouse effect, causing an increase in global temperatures that destabilized methane hydrate, a superconcentrated frozen gas. The methane release accounts for the shift in carbon isotopes and further enhanced the greenhouse effect, resulting in runaway global warming that contributed to the extinction. Studies of changes in oxygen isotope ratios have estimated the warming to be 6 degrees Celsius. Atmospheric scientists contend that a similar rise is not impossible by 2100. These findings therefore reinforce the urgency of addressing the problem of global warming in our time.

Q. Which of the following best characterizes the process that resulted from the Siberian volcanic eruptions as that process is described in the second paragraph?

c. A positive feedback loop


I'd charactierize it as (C), positive feedback loop. The warming did something to cause additional warming, which would then cause even more warming...etc. That's a positive feedback loop, just like when a sqealing microphone causes the sound to squeal even worse.
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 [#permalink] New post 11 May 2005, 04:58
OA is C.

Way to go supercat! This was a 700 point level question!
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 [#permalink] New post 14 May 2005, 04:28
can you giv me an example of a negative f/b loop? :oops:

Thanks

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 [#permalink] New post 14 May 2005, 10:32
doloris wrote:
can you giv me an example of a negative f/b loop? :oops:

Thanks

Best.


Well a positive feedback loop will make some value "run away" ... on the other hand a negative feedback loop will tend to keep some value stable.

Like the thermostat in your refrigerator. The cooling doesn't continue until everything freezes to absolute zero. Instead, it maintains a stable temperature. If the inside of the fridge is getting too warm, the refrigeration turns on. But once the fridge is cooled to the desired temperature, the refrigeration shuts off until needed again.
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 [#permalink] New post 14 May 2005, 19:00
Hey thanks supercat. :thanks

Best.
  [#permalink] 14 May 2005, 19:00
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