Chapter 24 Flashcards
search for extraterrestrial intelligence (SETI)
The name given to observing projects designed to search for signs of intelligent life beyond Earth.
extremophiles
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.
habitable zone
The region around a star in which planets could potentially have surface temperatures at which liquid water could exist.
selection effect (or selection bias)
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.
Cambrian explosion
The dramatic diversification of life on Earth that occurred between about 540 and 500 million years ago.
amino acids
The building blocks of proteins.
zones (on a jovian planet)
Bright bands of rising air that encircle a jovian planet at a particular set of latitudes.
astrobiology
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.
habitable world
A world with environmental conditions under which life could potentially arise or survive.
tree of life (evolutionary)
A diagram that shows relationships between different species as inferred from genetic comparisons.
fossil
Any relic of an organism that lived and died long ago.
K–T event (or impact)
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.
evolution (biological)
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.
Drake equation
An equation that lays out the factors that play a role in determining the number of communicating civilizations in our galaxy.
Martian meteorites
Meteorites found on Earth that are thought to have originated on Mars.
genetic code
The “language” that living cells use to read the instructions chemically encoded in DNA.
natural selection
The process by which mutations that make an organism better able to survive get passed on to future generations.
geological time scale
The time scale used by scientists to describe major eras in Earth’s past.
interstellar ramjet
A hypothesized type of spaceship that uses a giant scoop to sweep up interstellar gas for use in a nuclear fusion engine.
theory of evolution
The theory, first advanced by Charles Darwin, that explains how evolution occurs through the process of natural selection.
Fermi’s paradox
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.
stromatolites
Large bacterial “colonies.”
mutations
Errors in the copying process when a living cell replicates itself.
DNA (deoxyribonucleic acid)
The molecule that represents the genetic material of life on Earth.
