Life is thought to have begun as early as ______ years ago. One important event that took place in the long, early time span called the Precambrian was the appearance of ____ in Earth’s atmosphere, all of it produced as a by-product of photosynthesis carried out by a type of ______.

The Cambrian Explosion was an explosion in the number of ______ life-forms.

Each of the eras or periods within the geological timescale is characterized by a particular grouping of ______ preserved today as ______.

True or false: The first animals and plants evolved early in life’s history.

Life is generally regarded as having begun with the development of ______ molecules or chemical systems.

In what way are the bryophyte plants and the amphibian animals alike?

Put the following in the proper time sequence, earliest first:

a. first dinosaurs

b. first bacteria

c. first amphibians

d. first primates

e. oxygen accumulation in the atmosphere

f. first land plants

g. first birds

The time-frames in the geological timescale generally denote ____.

a. 10,000-year increments

b. 10-million-year increments

c. the reappearance of certain life-forms

d. transitions in life-forms

e. the appearance of larger life-forms

The first life on Earth may have been:

a. eukaryotic cells

b. RNA molecules

c. bacteria

d. formed on land

e. algae

Which of the following characteristics of early plants were adaptations to life on land? (Select all that apply.)

a. multicellularity

b. outer cuticle

c. photosynthesis

d. lack of vertical growth

e. internal embryonic development