The temperate conifer forests flanking the Cascade Mountains of the Pacific Northwest are a product of the regional climate. Frequent rain and fog encourage the growth of lush vegetation in a part of the world where cool Pacific storms march relentlessly shoreward from the north and west.
A million years from now, a geoscientist examining the fossils and sediments of the rocks that are currently being formed in this region will be able to say confidently that the climate had been moist and cool. Unless, that is, that scientist happened to be looking at rocks formed near Mount St. Helens or another of the active volcanoes in the range. Looking at these rocks, the scientist might think that the Pacific Northwest was a savannah or even a desert. According to Judith Harris of the University of Colorado Museum and John Van Couvering of the American Museum of Natural History, volcanically influenced ecosystems may look, in retrospect, as if they developed in a much drier regional climate than actually existed.
They named the phenomenon "mock aridity. " Their idea may explain why computer models tend to predict wetter climates than those suggested by the fossils. And it may mean that some paleoecologists will have to reevaluate their evidence. Explains Harris, "Volcanic activity makes for a barren environment. " After an isolated volcanic episode, a pioneering biological community will develop, followed by successional communities and, eventually, a climax community. When an ecosystem has reached climatic climax, it is a steady—state community that reflects the regional climate. But if volcanism is persistent, the biological community will never have the chance to reach climatic climax. It will bounce around between several pioneer and successional stages.
The possible implications are that some well—established paleoclimate stories might have to be rewritten. The two most significant examples are equatorial East Africa from the Miocene epoch (about 23 million years ago) to the present and the North American Great Plains from the Oligocene epoch (about 38 million years ago) to the present. Both have been interpreted as having woodland or savannah mosaic ecologies throughout each period. A savannah mosaic may consist of woodlands, treed grasslands and grasslands. Both areas, however, experienced persistent volcanism throughout each period. Had there been no volcanic activity, both regions might have appeared wetter. There might have been deciduous forests in North America and deciduous rain forests in East Africa.
A test of this idea, asserts paleoanthropologist Richard Potts, is to look at the global climate record in places where volcanism is not a factor. In the oceans, global temperature fluctuations are recorded in the oxygen—isotope ratios of marine sediments. These records are relatively immune to the local effects of terrestrial volcanism. "There you see the climatic change occurring later than what people have been seeing on land, " says Potts. This is consistent with Harris's suggestions about the regional climates of the North American Great Plains and equatorial East Africa. However, Potts says, the change is not steady and, in fact, fluctuations in the global climate have increased over the past 50 million years.
The ecosystems in these two examples developed during the transition from globally warm and wet climates of the Cretaceous period, which ended about 65 million years ago, to the climatically fluctuating ice ages of the past few million years. A big question among paleoecologists, particularly those who study human evolution, has been, when did the climate become cool and dry enough for forests to give way to savannah environments?
Question:
In using ocean records to test the idea that the Miocene savannah environments in the fossil record are an effect of volcanism, which of the following assumptions does Potts make?
[A] II only [B] III only [C] II and III [D] I, II and III
Option: 1 Explanation:
Where is testing of the mock aridity theory mentioned? Paragraph 5 discusses Potts' argument and evidence, that ocean sediments are shielded from volcanic fluctuations and therefore can better measure the actual variations in global temperature. Look for answer choices on which this line of reasoning relies. Start with RN III, which appears in three out of four choices. While ocean temperatures may not fluctuate as much as atmospheric temperatures disturbed by volcanoes, there's no reason to believe that the temperatures change more slowly. Eliminating RN III gets rid of all but (A). Verify RN II as a correct assumption: if marine sediments had been disturbed, they wouldn't be accurate baselines for measurement.
Wrong answers:
(B): Distortion. Any choice with RN III will trap those who confuse fluctuations with overall change.
(C): Distortion. As with (B), though slightly tougher to eliminate if you haven't predicted since it includes the correct RN II.
(D): Distortion. A grab—bag answer choice with all the flaws of its wrong components. RN I can't be correct either: if marine sediments formed as the result of volcanic activity, they wouldn't be good independent measures of climate. Potts specifically says to look at places where volcanism isn't a factor.
Strategy Point: Start with the Roman numeral that appears most frequently—this will potentially eliminate all but the correct answer choice.
Question:
With which of the following statements would Harris and Van Couvering most likely agree?
[A] Ecosystems near volcanoes were more successful than fossils indicate. [B] Computer models are more accurate gauges of ancient climate than fossils. [C] Persistent volcanism destroys the fossils and sedimentary rocks in the surrounding region. [D] There have been in fact no true deserts in the past few million years.
Option: 2 Explanation:
What do Harris and Van Couvering argue in the passage? They argue for the "mock aridity " model. Go back to paragraphs 2 and 3 to review. The author suggests that computer models predict wetter ancient climates, but up until now scientists have predicted drier ones because of fossils. A quick scan of the answer choices turns up (B) as something with which both scientists would certainly agree.
Wrong answers:
(A): Opposite. The mock aridity model describes a situation in which ecosystems near volcanoes struggle (paragraph 3).
(C): Opposite. Fossils have to have been found from volcanic regions, or there would never have been any misinterpretation of climate in the first place.
(D): Out of Scope. Nothing like this is mentioned in the passage.
Question:
If a geoscientist were to discover fossils that indicated that the Pacific Northwest was a savannah environment a million years ago, what effect would this development have on the argument of Harris and Van Couvering?
[A] It would strongly support the argument. [B] It would support the argument somewhat, but not conclusively. [C] It would neither support nor weaken the argument. [D] It would substantially weaken the argument.
Option: 3 Explanation:
Review what Harris and Van Couvering argue about fossils: fossils provide a misleading record of actual climate when there is volcanic activity nearby. If fossils were found in the volcanic region of the Pacific Northwest, it stands to reason that the climate
would appear drier than it actually was. No ground is gained or lost in their argument; the two scientists would make the same argument about these fossils as the others, without any additional evidence. A careful chain of thought will lead to (C).
Wrong answers:
(A): Opposite. The discovery adds no weight of evidence to the mock aridity theory.
(B): Opposite. As above.
(D): Opposite. Nor does the discovery weaken the theory, as it simply repeats the sort of findings that Harris and Van Couvering are challenging in the first place.
Question:
Which of the following would most challenge the idea that equatorial East Africa may have had a wetter climate than was previously suspected?
[A] Previous climate estimates were based on fossils from climax communities. [B] The fossil record contains no evidence of deciduous rain forests. [C] The level of volcanic activity in East Africa has never declined since the Miocene. [D] Computer models suggest that the climate in East Africa was warm.
Option: 1 Explanation:
If we're looking for evidence that will challenge a wet—environment theory, we're challenging the mock aridity theory. Where is evidence for the theory discussed? Primarily in paragraph 3. Review the main points: active volcanism keeps the ecosystem from developing into a climax community, which makes the whole region seem drier. What would make this point moot? If the fossils were taken from a climax community rather than one stunted by volcanism. (A) fits.
Wrong answers:
(B): Distortion. Check the end of paragraph 4, where deciduous forests are mentioned. It's argued that there might have been deciduous forests. The theory doesn't depend on it, and so the absence of evidence for it isn't a great blow.
(C): Opposite. This would support the argument for a wetter climate, since volcanism causes mock aridity.
(D): Opposite. Computer models that supported a warm environment wouldn't necessarily indicate a dry environment. Warmth and wetness go together in the passage.
Question:
In the passage, Harris is cited as making a claim that volcanic activity makes for a barren environment. This claim is:
[A] supported by the fact that no evidence of biological activity has been found in volcanic regions. [B] supported by an analogy of volcanic regions to another type of barren environment. [C] perhaps true, but not explicitly supported in the passage. [D] challenged by the author's claim that biological communities do develop in volcanic regions.
Option: 2 Explanation:
Review Harris' claim about volcanic activity and barren environments in paragraph 3. In a nutshell, she argues that volcanoes make the climate seem drier than it actually was. What is the author's opinion of the theory? Favorable, by every indication. This will help to focus attention on (B). Checking the passage for an analogy turns up the desert analogy in paragraph 2.
Wrong answers:
(A): Distortion. While biological activity found in volcanic regions may be misleading, Harris' theory is based on the idea that it does exist, it's just not accurate.
(C): Opposite. The author supports Harris' theory throughout the passage.
(D): Distortion. As in (A), mock aridity presumes that biological communities do develop in volcanic regions, just in a different way from the climate as a whole.
Strategy point: Turn abstractions into concretes. If an answer choice mentions an "analogy, " test it against the passage to find whether the specific analogy exists. If it mentions "another type of barren environment, " look for a specific example of the same. Leaving abstract ideas in the abstract makes evaluation difficult.
Question:
Suppose that the marine sediment record was found to show that global temperatures did not drop until well after the Miocene epoch. How would this finding be relevant to the passage?
[A] It would support the claim that volcanism had an extensive impact on global climate. [B] It would weaken the claim that the transition to a cooler climate occurred later than scientists thought. [C] It would weaken the claim that marine sediment records are immune to the effects of volcanism. [D] It would support the claim that some Miocene savannah environments are an effect of volcanism.
Option: 4 Explanation:
How would warm temperatures in the Miocene affect the climate? It would have been wetter also. If ocean sediments suggest warmth, then, they'd support the mock aridity theory and the idea that evidence of a Miocene savannah biome was really just the product of volcanoes. (D) matches the prediction.
Wrong answers:
(A): Distortion. The claim made by the mock aridity theory is that volcanism had a local, not global, impact.
(B): Opposite. This is the flip side of the correct answer. While the claim is correct, the evidence would clearly strengthen it since it shows that cooler climates came later than originally thought.
(C): Faulty Use of Detail. While the argument that ocean sediments are immune from volcanism is made, it's more likely that the discrepancy in the evidence mentioned in the question is because of volcanic effects than a problem with the evidence itself.
Question:
Suppose that the fossil record in a Pacific Rim country suggests that the region had a savannah ecology 38 million years ago. Harris and Van Couvering would most likely respond to this information by asserting that:
[A] the record inaccurately reflects the regional climate due to persistent volcanism. [B] the record may not be accurate if there was volcanic activity in the region. [C] the fossil record should no longer be used a source of information regarding global climate. [D] this supports their theory that volcanism can cause mock aridity.
Option: 2 Explanation:
An incorporation question. If a fossil record shows a savannah ecology, how would advocates of the mock aridity theory respond? They'd argue that volcanism might make things look like savannahs even though that are not. Be careful not to go too far and predict that they'd say volcanism was the cause. Proponents of the mock aridity theory aren't arguing that all seemingly savannah—like environments were actually just volcanoes, only that some probably are. Choice (B) fits this levelheaded prediction.
Wrong answers:
(A): Distortion. Without evidence of volcanoes in the area, they wouldn't make this claim.
(C): Distortion. Taking the argument too far again. They'd argue that fossil evidence has to be reevaluated in volcanic regions, not that fossils are useless.
(D): Out of Scope. There's nothing in the evidence given that would lend support to the theory.
