SAT Mc Graw Hill 2011

Questions 7–19 are based on the following passages.

The following passages are excerpts from a recent

debate between two well-known astronomers.

The author of Passage 1 is a professor of geolog-

ical sciences and the author of Passage 2 is a

principal scientist in the Department of Space

Studies in Boulder, Colorado.

PASSAGE 1

There is a cultural assumption that there

are many alien civilizations. This stems in no

small way from the famous estimate by Frank

Drake—known as the “Drake Equation”—that

was later amended by Drake and Carl Sagan.

They arrived at an estimate that there are per-

haps a million intelligent civilizations in the

Milky Way Galaxy alone.

The Drake and Sagan estimate was based

on their best guess about the number of plan-

ets in the galaxy, the percentage of those that

might harbor life, and the percentage of plan-

ets on which life not only could exist but

could have advanced to culture. Since our

galaxy is but one of hundreds of billions of

galaxies in the universe, the number of intelli-

gent alien species would be numbered in the

billions. Surely, if there are so many intelli-

gent aliens out there, then the number of

CHAPTER 16 / PRACTICE TEST 3 741

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planets with life must be truly astronomical.

But what if the Drake and Sagan estimates are

way off? If, as could be the reality, our civi-

lization is unique in the galaxy, does that

mean that there might be much less life in

general as well?

In my view, life in the form of microbes or

their equivalents is very common in the uni-

verse, perhaps more common than even Drake

and Sagan envisioned. However, complex life

is likely to be far more rare than commonly

assumed. Life on earth evolved from single

celled organisms to multi-cellular creatures

with tissues and organs, climaxing in animals

and higher plants. But is Earth’s particular

history of life—one of increasing complexity

to an animal grade of evolution—an inevitable

result of evolution, or even a common one?

Perhaps life is common, but complex life—

anything that is multicellular—is not.

On Earth, evolution has undergone a pro-

gressive development of ever more complex

and sophisticated forms leading ultimately to

human intelligence. Complex life—and even

intelligence—could conceivably arise faster

than it did on Earth. A planet could go from

an abiotic state to a civilization in 100 million

years, as compared to the nearly 4 billion

years it took on Earth. Evolution on Earth has

been affected by chance events, such as the

configuration of the continents produced by

continental drift. Furthermore, I believe that

the way the solar system was produced, with

its characteristic number and planetary posi-

tions, may have had a great impact on the

history of life here.

It has always been assumed that attaining

the evolutionary grade we call animals would

be the final and decisive step. Once we are at

this level of evolution, a long and continuous

progression toward intelligence should occur.

However, recent research shows that while

attaining the stage of animal life is one thing,

maintaining that level is quite another. The

geologic record has shown that once evolved,

complex life is subject to an unending succes-

sion of planetary disasters, creating what are

known as “mass extinction” events. These rare

First passage: Peter Ward, “Great Debates Part I,” Astrobiology
Magazine, 2003
Second passage: David Grinspoon, “Great Debates Part III,”
Astrobiology Magazine, 2003

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The passages below are followed by questions

based on their content; questions following a

pair of related passages may also be based on

the relationship between the paired passages.

Answer the questions on the basis of what is

statedor impliedin the passage and in any in-

troductory material that may be provided.