Why did Nonavian dinosaurs become extinct

Why did Nonavian dinosaurs become extinct?

Data from diverse sources, indicates that the Late Cretaceous climate was milder than today’s

because of shallow seas covering the continents. At the end of the Cretaceous, the geological

record shows that these seaways retreated from the continents back into the major ocean basins.

No one knows why. Over a period of about 100,000 years, while the seas pulled back, climates

around the world became dramatically more extreme: warmer days, cooler nights: hotter

summers, colder winters. Perhaps Nonavian dinosaurs(that is , all the dinosaurs except those

belonging to the Ave, or bird family) could not tolerate these extreme temperature changes and

become extinct.

1. According to paragraph 1, the presence of large amounts of water on continents during the

Late Cretaceous caused

A. climate conditions that were more extreme than today’s climate

B. reduction on the size of the major ocean basins around the world

C. temperatures that probably made it more difficult for some dinosaurs to survive

D. cooler summer temperatures and warmer winter temperate

If true though, why did ’cold-blooded’ animals, such as snakes, lizards, turtles, and crocodiles

survive the freezing winters and torrid summers? These animals are at the mercy of the climate

to maintain a livable body temperature. It’s hard to understand why they would not be affected,

whereas Nonavian dinosaurs were left too crippled to cope, especially if some dinosaurs were

‘warm-blooded’. Critics also point out that the shallow seaways had retreated from and advanced

on the continents numerous times during the Mesozoic, so why did the nonavian dinosaurs

survive the climatic changes associated with the earlier fluctuations but not with this one?

Although initially appealing, the hypothesis of a simple climatic change related to sea levels is

insufficient to explain all the data.

2. Which of the sentences below best expresses the essential information in the highlighted

sentence in the passage? Incorrect choices change the meaning in important ways or leave out

essential information.

A. Critics believe that the shallow seaways had advanced on and then retreated from the

continents significantly earlier, during the Mesozoic.

B. Another problem with this theory is that the nonavian dinosaurs survived many changes in

levels of the continental seas during Mesozoic.

C. Critics have not been able to explain why the nonavian dinosaurs survived the climatic changes

that happened when seas fell during the Mesozoic.

D. The continental sea rose and fell many times during the Mesozoic as well, but the resulting

climatic changes were not as severe.

3. In paragraph 2, why does the author bring up the fact that snake, lizards,turtles, and crocodiles

all survived extinction when nonavian dinosaurs did not?

A. To provide evidence that nonavian dinosaurs were particular sensitive to climate change

B. To argue that at least some dinosaurs were warm-blooded

C. To point out that snakes, lizards, turtles, and crocodiles were well adapted to the new climate

conditions

D. To challenge the idea that the extinction of nonavian dinosaurs was cased simply by climate

change

Volcanism, has also been implicated in dinosaur extinction. The end of the Cretaceous coincided

with a great increase in volcanic activity throughout the world. Lava flooded areas of India, and

explosive eruptions in the South Atlantic and the midwestern United States hurled ash over much

of the globe. These eruptions could have spewed great quantities of poisonous gases into the

atmosphere causing acid rain and more-acidic waters in the surface layers of the ocean. Over the

short term, a cooling would result from the airborne volcanic ash, which would cut off sunlight.

Over a longer term, warming could have resulted from the greenhouse effect. Climatic changes

from increased volcanism may have caused the extinction of many nonavian dinosaurs, but they

do not satisfactorily explain the selective patterns of extinction in the fossil record.

4. According to paragraph 3, the increase in volcanism does NOT explain which of the following?

A. which species become extinct and which survived

B. why climate mate seems to have become temporally cooler

C. Changes in water acidity in the surface layers of the ocean

D. The presence of poisonous gases in the atmosphere

Dissatisfaction with conventional explanations for nonavian dinosaur extinctions eventually led to

a key observation that, in turn, has fueled a decade of vigorous and often vitriolic debate. Many

plants and animals that become extinct at the end of the Mesozoic disappear abruptly as one

moves from older layers of rock documenting the end of the Cretaceous up into younger rocks

representing the beginning of the Cenozoic. Between the last layer representing the end of the

Cretaceous and the first layer representing the start of the Cainozoic, there is often a thin bed of

clay. Scientists felt that they could get an idea of how long it took to deposit this 1 centimeter of

clay by looking at the concentration of the element iridium in it.

5. The word “vigorous” in the passage is closest in meaning to

A. energetic

B. scientific

C. continuous

D. productive

6. The word “abruptly” in the passage is closest in meaning to

A. suddenly and unexpectedly

B. initially

C. eventually

D. with explanation

7. Paragraph 4 suggests that scientists were initially interested in the layer of clay because they

wanted to know which of the following about the Earth’s history?

A. what the climate was like at the start of the Cenozoic period

B. the levels of iridium in rocks from the Cenozoic compared with levels in rocks from the

Cretaceous

C. how this bed of clay formed such an extremely thin layer

D. whether there was a connection between the clay and how quickly extinction occurred

Iridium is no longer common at Earth’s surface. Because it usually exists in a metallic state, it was

preferentially incorporated into Earth’s core as the planet cooled and consolidated. Iridium is

found in high concentrations in some meteorites in which the solar system’s original chemical

composition is preserved. Even today, microscopic meteorites continually bombard Earth, falling

on both land and sea. By measuring how many of these meteorites fall to Earth over a given

period of time, scientists can estimate how long it might have taken to deposit the observed

amount of iridium in the boundary clay. These calculations suggest that a period of about 1

million years would have been required. On the basis of other evidence related to Earth’s

magnetic field at the time of the extinction, however, it was believed that nonavian dinosaurs

and other animals had to have gone extinct within a period of half a million years. If so, the

deposition of the boundary clay could not have lasted 1 million years, and the unusually high

concentration of iridium seemed to require a special explanation.

8. The word “continually” in the passage is closest in meaning to

A. occasionally

B. obviously

C. regularly

D. generally

9. Which of the following can be inferred form paragraph 5 about iridium?

A. It was present at the time the solar system originally formed

B. There is very little iridium found in Earth ’s core

C. Iridium on meteorites is rarely in its metallic state

D. At hight levels iridium toxic enough to have caused mass extinctions

10. According to paragraph 5, as a result of determining how long it took to despot the

iridium-rich boundary clay, scientists realized that

A. meteorites had stopped falling to Earth while the boundary clay was being deposited

B. the thin bed of boundary clay was formed over a period of about one million years

C. the thin bed of boundary clay layer was older than they previously thought

D. the iridium in the boundary clay could not have been deposited through the usual process

Consequently, scientists hypothesized that a single large asteroid, about 10 to 15 kilometers

across, collided with Earth, and the resulting fallout created the boundary clay. Their calculations

show that the impact kicked up a dust cloud that cut off light for several months, inciting

photosynthesis in plants; decreased surface temperatures on continents to below freezing;

caused extreme episodes of acid rain; and significantly raised long-term global temperatures

through the ‘greenhouse effect,’ This disruption of the food chain an climate would have

eradicated the nonavian dinosaurs and other organisms in less than 50 years.

11. The word “eradicated” in the passage is closest in meaning to

A. reached

B. starved

C. affected

D. eliminated

12. According to paragraph 6, the dust produced by the large asteroid collided with Earth led to

all of the following Except

A. a short-term drop in temperatures on land

B. loss sunlight for several months

C. temperately freezing of much the world’s oceans

D. warmer climate over the long term

13. Look at the four squares [♦] that indicate where the following sentence could be added to the

passage. Where would the sentence best fit?

These large bodies of water kept the temperature of the nearby air bodies relatively constant

from day to night, summer to winter.

Data from diverse sources, indicates that the Late Cretaceous climate was milder than today’s

because of shallow seas covering the continents.♦ At the end of the Cretaceous, the geological

record shows that these seaways retreated from the continents back into the major ocean

basins.♦ No one knows why.♦ Over a period of about 100,000 years, while the seas pulled back,

climates around the world became dramatically more extreme: warmer days, cooler nights:

hotter summers, colder winters.♦ Perhaps Nonavian dinosaurs(that is , all the dinosaurs except

those belonging to the Ave, or bird family) could not tolerate these extreme temperature changes

and become extinct.

14. The nonavian dinosaurs became extinct at the end of the Cretaceous period, and scientists

have proposed several theories to explain why.

Answer Choices

A. Increase volcanic activity led to acid rain, a short-term cooling of the atmosphere, and other

harmful effects, but it does not explain the selective patterns of extinction

B. The clay at Cretaceous - Cenozoic boundary is unusually rich in iridium, which suggests that the

extinctions were caused by Earth’s collision with large asteroid

C. Loss of continental seas made the climate more extreme, but some cold-blooded animals

survived the change and the seas had retreated before without massive extinctions.

D. There is evidence that calls into question the hypothesis that the seas retreated from the

continents at the end of the Cretaceous period

E. Evidence of volcanic activity, during the Cretaceous period supports the huge and widespread

volcanic eruptions triggered the mass extinction.

F. Evidence of volcanic activity, during the Cretaceous period supports the huge and widespread

volcanic eruptions triggered the mass extinction.