Chapter 24

Question 1

search for extraterrestrial intelligence (SETI)

Answer 1

The name given to observing projects designed to search for signs of intelligent life beyond Earth.

Question 2

extremophiles

Answer 2

Living organisms that are adapted to conditions that are “extreme” by human standards, such as very high or low temperature or a high level of salinity or radiation.

Question 3

habitable zone

Answer 3

The region around a star in which planets could potentially have surface temperatures at which liquid water could exist.

Question 4

selection effect (or selection bias)

Answer 4

A type of bias that arises from the way in which objects of study are selected and that can lead to incorrect conclusions. For example, when you are counting animals in a jungle it is easiest to see brightly colored animals, which could mislead you into thinking that these animals are the most common.

Question 5

Cambrian explosion

Answer 5

The dramatic diversification of life on Earth that occurred between about 540 and 500 million years ago.

Question 6

amino acids

Answer 6

The building blocks of proteins.

Question 7

zones (on a jovian planet)

Answer 7

Bright bands of rising air that encircle a jovian planet at a particular set of latitudes.

Question 8

astrobiology

Answer 8

The study of life on Earth and beyond; it emphasizes research into questions of the origin of life, the conditions under which life can survive, and the search for life beyond Earth.

Question 9

habitable world

Answer 9

A world with environmental conditions under which life could potentially arise or survive.

Question 10

tree of life (evolutionary)

Answer 10

A diagram that shows relationships between different species as inferred from genetic comparisons.

Question 11

fossil

Answer 11

Any relic of an organism that lived and died long ago.

Question 12

K–T event (or impact)

Answer 12

The collision of an asteroid or comet 65 million years ago that caused the mass extinction best known for wiping out the dinosaurs. K and T stand for the geological layers above and below the event.

Question 13

evolution (biological)

Answer 13

The gradual change in populations of living organisms responsible for transforming life on Earth from its primitive origins to the great diversity of life today.

Question 14

Drake equation

Answer 14

An equation that lays out the factors that play a role in determining the number of communicating civilizations in our galaxy.

Question 15

Martian meteorites

Answer 15

Meteorites found on Earth that are thought to have originated on Mars.

Question 16

genetic code

Answer 16

The “language” that living cells use to read the instructions chemically encoded in DNA.

Question 17

natural selection

Answer 17

The process by which mutations that make an organism better able to survive get passed on to future generations.

Question 18

geological time scale

Answer 18

The time scale used by scientists to describe major eras in Earth’s past.

Question 19

interstellar ramjet

Answer 19

A hypothesized type of spaceship that uses a giant scoop to sweep up interstellar gas for use in a nuclear fusion engine.

Question 20

theory of evolution

Answer 20

The theory, first advanced by Charles Darwin, that explains how evolution occurs through the process of natural selection.

Question 21

Fermi’s paradox

Answer 21

The question posed by Enrico Fermi about extraterrestrial intelligence—”So where is everybody?”—which asks why we have not observed other civilizations even though simple arguments would suggest that some ought to have spread throughout the galaxy by now.

Question 22

stromatolites

Answer 22

Large bacterial “colonies.”

Question 23

mutations

Answer 23

Errors in the copying process when a living cell replicates itself.

Question 24

DNA (deoxyribonucleic acid)

Answer 24

The molecule that represents the genetic material of life on Earth.