Which of the following is true of life on Earth?

Which of the following is true of life on Earth?
 
  A) Life, in the form of multicellular organisms, has existed on Earth for only about 2 million years.
  B) Life has existed on Earth for at least 3.4 billion years.
  C) The Cambrian explosion marks the formation of the first unicellular organisms on Earth.
  D) Complex multicellular organisms were present on Earth 2.5 billion years ago.

Question 2

Offspring born with random alterations to their DNA are called__________.
 
  A) clones
  B) drones
  C) mutants
  D) fossils

Question 3

Which of the following is true of wavelengths of signals sent into space?
 
  A) Wavelengths longer than 100 cm are absorbed in Earth's atmosphere.
  B) The interval between the 21-cm spectral line of neutral hydrogen and the 18-cm line of OH has very high background interference.
  C) Wavelengths longer than 100 cm get lost in the background noise of the Milky Way Galaxy.
  D) The interval between the 21-cm spectral line of neutral hydrogen and the 18-cm line of OH is narrow and can be monitored easily.

Question 4

Which of the following is true of natural selection?
 
  A) It is a random occurrence.
  B) It does not occur in most species of organisms.
  C) It is directed by changes in the environment.
  D) It does not lead to evolution of a species.

Question 5

Which of the following is true of the origin of life on Earth?
 
  A) Evidence suggests that the earliest living things contained hard bones and shells.
  B) The oldest living fossils indicate that life began on land.
  C) Evidence suggests that the earliest living things were multicellular and gigantic.
  D) The oldest fossils indicate that life began in the sea.

Question 6

The _____ is the interval of the radio spectrum between the 21-cm hydrogen emission line and the 18-cm OH emission line; these are likely wavelengths to use in the search for extraterrestrial life.
 
  A) water hole
  B) habitable zone
  C) Arecibo beacon
  D) DNS zone