1. Unit 2 Review: History of Life on Earth

2. What proportion of all species that have ever lived has become extinct?
less than 1 percent
approximately one-half
more than 99 percent
100 percent

3. Most fossils form in
rusty water
volcanic rock.
sedimentary rock.
the sap of ancient trees.

4. The length of time required for half of the radioactive atoms in a sample to decay is its
half-life.
relative date.
radioactive date.
period.

5. To compare the relative ages of fossils, scientists sometimes use an easily recognized species called a(an)
carbon fossil.
radioactive fossil.
index fossil.
sedimentary fossil.

6. After Precambrian Time, the basic divisions of the geologic time scale, from larger to smaller are
eras and periods.
periods and eras.
relative and absolute dates.
billions of years and millions of years.

7. The Mesozoic Era occurred
before Precambrian Time.
during Precambrian Time.
after the Paleozoic Era.
after the Cenozoic Era.

8. Earth’s most recent era is the
Paleozoic.
Mesozoic.
Cenozoic.
Precambrian.

9. Fossilized evidence of Earth’s first forms of life would consist of
vertebrates from the Precambrian.
invertebrates from the Precambrian.
eukaryotes from the Precambrian.
prokaryotes from the Precambrian.

10. Why did oceans not exist on Earth nearly 4 billion years ago?
No water molecules were present.
Water remained a gas because Earth was very hot.
Water existed as ice because Earth was very cold.
There was no oxygen gas in the atmosphere.

11. Which of the following was NOT characteristic of Earth before the oceans formed?
volcanic activity
bombardment by comets and asteroids
an atmosphere of poisonous gases
an atmosphere containing oxygen gas

12. One necessary condition for the evolution of the first life on Earth was
the presence of DNA.
abundant oxygen in the atmosphere.
the presence of photosynthetic organisms.
the presence of liquid water.

13. The first organisms on Earth were most like today’s
bacteria.
eukaryotes.
multicellular organisms.
DNA molecules.

14. The Cambrian Explosion resulted in the evolution of the first
dinosaurs and mammals.
representatives of most animal groups.
bacteria.
land animals.

15. A very large mass extinction in which amphibians and trilobites disappeared occurred at the end of the
Precambrian.
Cambrian Period.
Paleozoic Era.
Quaternary Period.

16. During the Jurassic and Cretaceous periods, the dominant land animals were
amphibians.
dinosaurs.
grazing mammals.
human ancestors.

17. A fossilized dinosaur, found with fossils of the flowering plants that it ate, must have lived
since life first evolved.
before the Mesozoic Era.
during the Mesozoic Era.
after the Mesozoic Era.

18. What does fossil evidence indicate about the order in which these three vertebrates evolved: a bony fish with a jaw, a jawless fish, and a fish with leglike fins?
The bony fish evolved before the jawless fish.
The fish with leglike fins was the last to evolve.
The jawless fish was the last to evolve.
The fish with leglike fins evolved before the jawless fish.

19. What does fossil evidence indicate about the order in which these three vertebrates evolved: a bony fish with a jaw, a jawless fish, and a fish with leglike fins?
The bony fish evolved before the jawless fish.
The fish with leglike fins was the last to evolve.
The jawless fish was the last to evolve.
The fish with leglike fins evolved before the jawless fish.

20. In the past, mass extinctions encouraged the rapid evolution of surviving species
by changing developmental genes.
by making new habitats available to them.
because they killed all organisms that had coevolved.
because they spared all organisms that had evolved convergently.

21. A single species that has evolved into several different forms that live in different ways has undergone
adaptive radiation.
coevolution.
punctuated equilibrium.
mass extinction.

22. A pattern in which species experience long, stable periods interrupted by brief periods of rapid evolutionary change is called
convergent evolution.
Co evolution.
adaptive radiation.
punctuated equilibrium.

23. In a species that has become ____________________, all members have died, and the species has ceased to exist.

24. extinct

25. The ____________________ record provides evidence about the history of life on Earth

26. fossil

27.   A researcher could quickly date a new rock sample if it contained a(an) ____________________ fossil.

28. Index

29. After Precambrian Time, the main divisions of the geologic time scale are eras and ____________________.

30. periods

31. As the Paleozoic Era closed, a(an) ____________________, which is the dying out of many types of living things at one time, occurred.

32. Mass extinction

33. ____________________ is the process by which two species evolve in response to changes in each other over time.

34. Co evolution

35. The similar body structure but different ancestry of sharks and dolphins indicates that these groups have undergone _________________________, a process in which unrelated organisms come to resemble each other

36. Convergent evolution