History of Life Worksheets

Studying the History of Life www.ck12.org

1.1 Studying the History of Life
Name___________________ Class_______
Date______________________
Write true if the statement is true or false if the statement is false.

______ 1. Fossilization most often preserves soft body parts.

______ 2. Paleontologists are scientists who study fossils.
______ 3. Index fossils can help identify rock layers of the same
age in different places.
______ 4. Relative dating relies on the position of fossils within a
rock column.
______ 5. Carbon-14 dating can be used to date fossils that are up
to 6 million years old.
______ 6. Radioactive decay is a random process that occurs at a
fixed rate.
______ 7. Molecular clocks support a universal common ancestor
for all life.
______ 8. Eras of the geologic time scale are divided into eons.
______ 9. Only one mass extinction has ever occurred in the
history of life on Earth.
______ 10. The fossil record does not support the idea of a
common ancestor of all life on Earth.
______ 11. The rate of evolution is always the same.
______ 12. Geographic changes can affect patterns of evolution.

Critical Reading
Read this passage from the lesson and answer the questions that
follow.
A Geologic Time Scale Measures the Evolution of Life
Observation of rock layers, dating techniques, and correlation of
similar strata from around the world led to the development of a
geologic time scale. How does the scale divide the 4.6 billion years
of Earth’s history? What themes emerge from its stories of the
past? One theme is the almost unimaginable amounts of time in
Earth’s history. The deep time of Earth’s history is far beyond our
experience, and our knowledge is far more detailed for recent
periods than for the distant past. A scale divided into evenly spaced
periods of time would not show this recent detail, so the divisions
of the geologic time scale are not evenly spaced. Instead, they
mark major changes in Earth’s climate, geography, atmosphere,
and life. In the geologic time scale, the largest units of time are
eons. Eons include smaller units called eras, which in turn include
periods, epochs, and stages. Faunal stages identify specific fossil
groups. Terms such as upper (or late) and lower (or early) may be
used to divide units into more or less recent subdivisions. The total
history of Earth comprises four eons. From most to least recent
they are the Phanerozoic, Proterozoic, Archean, and Hadean. Their
names refer to a second major theme of Earth’s history: the
evolution of life. Phanerozoic means “visible life.” The
Phanerozoic Eon spans the most recent 545 million years of
Earth’s history. It is divided into three eras well known for their
chronicle of life in the fossil record:
• The Cenozoic (“recent life”) Era is the present era. It is the era
we humans live in.
• The Mesozoic (“middle life”) Era precedes the Cenozoic Era. It
is the middle era of the Phanerozoic Eon.
• The Paleozoic (“old life”) Era is oldest era of the Phanerozoic
Eon. It begins with the Cambrian Period, when the first great
explosion of life occurred. For the first time in the Cambrian,
living things were composed of hard parts that turned to fossils and
left a record of their lives. (The name “Cambrian” refers to where
these fossils were first studied.)
Proterozoic means “before complex life.” The Proterozoic Eon
precedes the Phanerozoic Eon. It extends back to 2.5 billion years
ago. The Archean (“ancient”) Eon precedes the Proterozoic Eon.
The Hadean (“unseen”) Eon reaches back to the formation of
Earth. These three oldest eons are combined in the Precambrian
Supereon, which includes all of Earth’s history up to the Cambrian
explosion of life.

Questions
1. How long is the history of Earth?
- The history of the Earth is 4.6 billion years long.
-
-

2. What is the basis for divisions of the geologic time scale?

-
- Earth’s geological time scale is divided into: eons, era, periods, epochs
and stages.
-

3. What is the most recent eon of the geologic time scale, and what
eras does it include?
-
The most recent eon is the Phanerozoic and it includes the Paleozoic,
- Mesozoic, and Cenozoic Eras.
-

4. Briefly describe the first three eons of Earth’s history.

-
- Hadean: Origin of Earth and the oldest known rocks.
- Archaean: Oldest fossil cells, oxygenated atmosphere.
Proterozoic: Oldest eukaryotic fossil, algae and soft -bodied invertebrate anim
appear.
5. Why is the Cambrian Period such an important division of the
geologic time scale?
- The Cambrian Period is an important division because now that it shows
- the first sudden increase of many animals.
-
Multiple Choice
Circle the letter of the correct choice.

1. If rock layers are undisturbed, the lowest layers are

a. oldest.
b. newest.
c. youngest.
d. most recent.

2. The method of dating fossils that provides an approximate age in

years is called
a. relative dating.
b. absolute dating.
c. geologic dating.
d. rock-layer dating.

3. The time it takes half of a given amount of a radioactive element

to decay is its
a. isotope.
b. half-life.
c. light-year.
d. molecular clock.

4. Isotopes used to measure the ages of rocks and fossils include

a. carbon-14.
b. uranium-238.
c. potassium-40.
d. all of the above.
5. Which choice lists the divisions of the geologic time scale from
largest to smallest?
a. era-eon-epoch-period
b. period-eon-epoch-era
c. epoch-era-eon-period
d. eon-era-period-epoch

6. Eukaryotic cells first appeared in the fossil record about

a. 4.2 billion years ago.
b. 3.5 billion years ago.
c. 1.8 billion years ago.
d. 0.5 billion years ago.

7. Massive geographic changes that occurred during Earth’s history

are explained by the theory of
a. plate tectonics.
b. adaptive radiation.
c. quantum evolution.
d. episodic speciation.

Vocabulary
Match the vocabulary term with the correct definition.
Term
____ 1. adaptive radiation
____ 2. coevolution
____ 3. coextinction
____ 4. convergent evolution
____ 5. divergent evolution
____ 6. gradualism
____ 7. macroevolution
____ 8. microevolution
____ 9. punctuated equilibrium
____ 10. quantum evolution

Definition
a. increased risk of extinction in interdependent species when one
of the species goes extinct
b. type of evolution in which closely related species become less
similar
c. evolution in taxa higher than the species level
d. idea that evolution occurs infrequently but rapidly
e. evolution within a population or species
f. type of evolution in which distantly related species become more
similar
g. idea that higher taxa originated in response to drastic
environmental changes
h. rapid evolution from a single species to several species to fill a
diversity of niches
i. idea that evolution occurs via slow, steady change
j. type of evolution in which two species influence each other’s
evolution

1.2 Early Life

True or False
Write true if the statement is true or false if the statement is false.

______ 1. There is fossil evidence for life during the Hadean Eon.
______ 2. Most scientists agree that organic molecules arose
before cells.
______ 3. The metabolism-first model is the idea that biochemical
pathways evolved before replicator molecules.
______ 4. Archaebacteria are thought to have evolved from
Eukaryota.
______ 5. Comets and meteors are known to contain organic
molecules.
______ 6. A single LUCA is thought to have given rise to all
cellular life on Earth.
______ 7. The oldest known fossils represent photosynthetic
organisms.
______ 8. The earliest prokaryotes lacked cell membranes.
______ 9. Massive deposits of iron ore formed when Earth first
became a planet.
______ 10. Ozone in the atmosphere protects Earth from harmful
radiation.
______ 11. Endosymbiotic theory is no longer accepted by most
scientists.
______ 12. Mitochondria have the same DNA sequences as the
DNA in the nucleus.
Critical Reading
Read this passage from the lesson and answer the questions that
follow.
Formation of Earth: We are Made of Stardust!

Earth began as the solar system began—often described as a giant

rotating cloud of dust, rocks, and gas. “Dust, rocks, and gas” may
not sound inspiring, but this cloud contained the 92 elements, or
kinds of atoms, that combine to form everything—both living and
nonliving—of the wonderful world we inhabit. The Big Bang (9
billion years earlier!) produced atoms of hydrogen and helium.
Elements as heavy as lithium followed the Big Bang within
minutes. Stars such as red giants fused hydrogen and helium nuclei
to form elements from carbon (the foundation of life!) to calcium
(now in our bones and teeth). Supernova explosions formed and
ejected heavier elements such as iron (found in red blood cells).
We are not just “dust.” We—and our world—are stardust! How did
this rotating cloud of stardust become our solar system? One
theory suggests that a nearby supernova sent a shock wave through
a cloud of stardust, increasing its spin to form a protoplanetary
disk. Most of the mass concentrated in the middle of the disk,
which began to heat up. Eventually, heat in this central core began
nuclear fusion of hydrogen to helium, and the core ignited. The sun
was born. Matter outside the sun’s gravity separated into rings of
debris. Collisions of objects within the rings formed larger objects.
These were protoplanets that would eventually became the planets
of the solar system. One protoplanet, about 150 million kilometers
from the sun, would become Earth. Solar wind cleared much of the
remaining nonplanetary material from the disk. Early Earth was
very different from the Earth we know today. The planet was
bombarded by debris and heated by radioactive decay and the
pressure of contraction. As a result, Earth was molten at first.
Heavy elements sank to the center, and lighter ones traveled to the
surface. Heat and solar wind meant that early Earth had no
atmosphere or oceans. Eventually, contraction and cooling allowed
formation of a crust and retention of an atmosphere. However,
continued bombardment melted portions of the crust for a long
time. About 4.5 billion years ago, Earth collided with another
protoplanet, named Theia. This “Big Whack” gave Earth its moon
and tilted Earth on its current axis. The tilt led to the seasons,
which now influence so much of life’s diversity.
The Big Whack may also have initiated plate tectonic activity by
speeding up Earth’s rotation. The day/night cycle during the
Hadean Eon may have been as short as 10 hours. Since then, the
moon’s tidal drag may have resulted in Earth’s slower rotation.
As Earth continued to cool amidst heavy bombardment, steam
escaped from the crust and active volcanoes released other gases to
form a primitive atmosphere. The early atmosphere was reddish in
color and would have been toxic to modern multicellular
organisms. It contained ammonia, methane, water vapor, carbon
dioxide, and nitrogen, but no more than a trace of oxygen. In the
absence of oxygen, no ozone layer protected Earth from the sun’s
ultraviolet rays. Between 4.2 and 3.8 billion years ago, clouds
produced rain, which formed the oceans. The early oceans were
olive green.
Questions
1. Explain how stardust became our solar system.
- One theory suggests that a nearby supernova sent a shock wave through a cloud of
- stardust, increasing its spin to form a protoplanetary disk. Most of the mass
- concentrated in the middle of the disk, which began to heat up.

2. In detail, describe early Earth.

- Early Earth had no ozone layer and was probably very hot. The early
- Earth also had no free oxygen. Without an oxygen atmosphere very few
- things could live on the early earth.

3. What happened when Earth collided with the protoplanet Theia?

- This "Big Whack" gave Earth its moon and tilted Earth on its current axis. The tilt led to
- the seasons, which now influence so much of life's diversity. The Big Whack may also have
initiated plate tectonic activity by speeding up Earth's rotation. The day/night cycle
- during the Hadean Eon may have been as short as 10 hours.

4. Describe Earth’s early atmosphere.

- The early atmosphere was reddish in color and would have been toxic to modern
- multicellular organisms. It contained ammonia, methane, water vapor, carbon
- dioxide, and nitrogen, but no more than a trace of oxygen.

5. How did early Earth’s oceans form? What did they look like?
-
Between 4.2 and 3.8 billion years ago, clouds produced rain,
- which formed the oceans. The early oceans were olive green.
-

Multiple Choice
Circle the letter of the correct choice.

1. The solar system formed from a

a. protocell.
b. protoplasm.
c. protoplanet.
d. protoplanetary disk.

2. Miller and Urey tested the hypothesis that conditions on

primitive Earth would have allowed the
a. formation of living cells from organic molecules.
b. synthesis of organic molecules from inorganic precursors.
c. evolution of eukaryotic organisms from prokaryotic organisms.
d. development of DNA and RNA from primitive protein
molecules.

3. The idea that a replicator molecule evolved before the evolution

of biochemical pathways is known as the
a. metabolic-pathway model.
b. endosymbiotic model.
c. genes-first model.
d. replicator model.

4. The exogenesis hypothesis is supported by the discovery of

a. Archaebacteria in hydrothermal vents.
b. circular DNA in mitochondria.
c. living cells in black smokers.
d. organic molecules in space.

5. The earliest life on Earth most likely evolved during the

a. Proterozoic Eon.
b. Primitive Eon.
c. Primeval Eon.
d. Hadean Eon.

6. Not long after prokaryotic cells evolved, they split into two
major groups, called the Eubacteria and the
a. Protista.
b. Eukaryota.
c. Mitochondria.
d. Archaebacteria.

7. Before the evolution of photosynthesis, organisms were

a. aerobic.
b. symbiotic.
c. anaerobic.
d. eukaryotic.

Vocabulary
Match the vocabulary term with the correct definition.

Term
____ 1. protocell
____ 2. prokaryote
____ 3. heterotroph
____ 4. chemoautotroph
____ 5. glycolysis
____ 6. photosynthesis
____ 7. anaerobe
____ 8. eukaryote
____ 9. endosymbiont
____ 10. stromatolite
Definition
a. organism that feeds on other organisms
b. pathway for transferring energy from organic molecules to ATP
c. organism that requires an environment without oxygen
d. mat of photosynthetic microorganisms
e. organism that lives inside the cells of another organism
f. simple, membrane-enclosed early metabolic unit
g. use of sunlight to make carbohydrates from carbon dioxide and
water
h. single-celled organism that lacks a nucleus
i. organism whose DNA is enclosed within a nuclear membrane
j. organism that extracts energy from inorganic molecules

1.3 Multicellular Life

True or False
Write true if the statement is true or false if the statement is false.

______ 1. The first animals evolved before the first true plants.
______ 2. The evolution of sexual reproduction may have
increased the rate of evolution.
______ 3. Arthropods called trilobites first appeared in the
Permian Period.
______ 4. There has been only one supercontinent in Earth’s
history.
______ 5. Evolution of lobe-like fins allowed vertebrates to
eventually move from the ocean to the land.
______ 6. Levels of oxygen in the air were lower during the
Carboniferous Period than they are now.
______ 7. Pangaea formed during the Permian Period of the
Paleozoic Era.
______ 8. There was a resurgence of evolution at the beginning of
the Mesozoic Era.
______ 9. The Paleogene Period was the golden age of large
dinosaurs.
______ 10. The K-T extinction occurred at the end of the
Cretaceous Period.
______ 11. Homo erectus was probably the first hominid to leave
Africa.
______ 12. There has been a decrease in carbon dioxide since the
Industrial Revolution.

Critical Reading
Read this passage from the lesson and answer the questions that
follow.
Introduction
The history of life reaches the last billion years of Earth’s 4.6
billion-year history with no hint of the wondrous diversity of life
as humans know it. Not until nearly 80% of Earth’s history had
passed did multicellular life evolve. The fossil record tells the
story: millions of species of fish, amphibians, reptiles, birds,
mammals, mosses, ferns, conifers, flowering plants, and fungi
eventually populated the seas and covered Earth, as continents
crashed together and broke apart, glaciers advanced and retreated,
and meteors struck, causing massive extinctions. Biologists
estimate that 99% of the species that have ever lived on Earth are
now extinct. Nonetheless, up to 80 million species populate our
world today. Life has had a colorful and exciting last billion years,
spawning diversity almost beyond our comprehension. And yet,
the giant steps of evolution remain back in the Precambrian. Its
catalog of evolutionary innovations is long and impressive:
• Energized elements from stardust formed simple organic
molecules.
• Building blocks chained together to form catalysts and self-
replicating macromolecules.
• Biochemical pathways evolved.
• Protective yet permeable membranes enclosed the catalysts,
replicators, and their metabolic retinue.
• Early prokaryotic cells “learned” to make ATP by splitting
glucose.
• Other cells began to harvest the energy of sunlight through
photosynthesis.
• Photosynthetic cyanobacteria produced vast amounts of “waste”
oxygen, dramatically altering Earth’s atmosphere.
• The oceans rusted and iron ore was deposited.
• An ozone layer formed, shielding life from UV radiation.
• The “oxygen catastrophe” killed many anaerobic prokaryotes.
• Still other prokaryotes “learned” to use the new oxygen to release
the energy remaining in carbohydrate products of glycolysis.
• Endosymbiosis created eukaryotes, firmly establishing the three
major evolutionary lineages, which today still comprise the living
world.

The timing and exact nature of most of these innovations is

speculative; indeed, the first few may have been extraterrestrial
and even deeper in time. They comprise perhaps the most
important landmarks in the evolution of life, but the fossil record is
sketchy due to prokaryote size, rock layer metamorphosis, and
burial by more recent rocks.

Questions
1. At what point in Earth’s history did multicellular life evolve?
- After 80% of Earth's history.
-
-
2. State the number of species and the percent of Earth’s total
species that exist today.
- There are about 80 million species populating the Earth today. This
- makes up about a 1% of Earth's total population.
-
3. List significant events that occurred in the early evolution of life
on Earth up through the evolution of early prokaryotes.
- •• Energized elements from stardust formed simple organic molecules.
Building blocks chained together to form catalysts and self- replicating macromolecules.
- • Biochemical pathways evolved.
• Protective yet permeable membranes enclosed the catalysts, replicators, and their metabolic
- retinue.
4. How did the evolution of photosynthesis by cyanobacteria affect
early Earth and its life forms?
- The evolution of photosynthesis by cyanobacteria created a lot of "waste" oxygen
- which altered the Earth's atmosphere.
-
5. Why is the fossil record sketchy for the early evolution of life on
Earth?
- The fossil record is sketchy due to prokaryote size, rock layer metamorphosis,
and burial by more recent rocks.
-
-

Multiple Choice
Circle the letter of the correct choice.

1. The evolution of sexual reproduction occurred about

a. 4 billion years ago.
b. 3 billion years ago.
c. 2 billion years ago.
d. 1 billion years ago.

2. Nearly all modern animal phyla first appeared during the

a. Neogene Period.
b. Cambrian Period.
c. Cretaceous Period.
d. Quaternary Period.

3. Which statement is true about the first fish?

a. They had scaly skin and claws.
b. They lacked jaws and had armor.
c. They spent part of the time on land.
d. They evolved during the Jurassic Period.

4. The evolution of eggs with shells allowed vertebrates to

a. outcompete fish.
b. reproduce on land.
c. survive in the water.
d. live on the ocean floor.

5. The massive Permian extinction allowed an adaptive radiation of

a. amphibians.
b. dinosaurs.
c. hominids.
d. humans.

6. During the Paleocene, mammals took over ecological niches

formerly occupied by
a. birds.
b. fishes.
c. insects.
d. dinosaurs.

7. What is the main cause of the “sixth extinction”?

a. human actions
b. impact events
c. glaciations
d. megafauna

Vocabulary Match the vocabulary term with the correct definition.

Term
____ 1. Paleozoic Era
____ 2. trilobite
____ 3. liverwort
____ 4. Permian Period
____ 5. Mesozoic Era
____ 6. Pangaea
____ 7. Jurassic Period
____ 8. Cenozoic Era
____ 9. Paleocene Epoch
____ 10. Holocene Epoch
Definition
a. first true plant to live on land
b. supercontinent that eventually broke up into all the continents
we know today
c. most recent era of the geologic time scale
d. geologic era that starts with the Cambrian Period
e. first epoch of the Cenozoic Era
f. era known as the “age of dinosaurs”
g. current epoch of the geologic time scale
h. arthropod that was common during the Cambrian Period
i. last period of the Paleozoic Era
j. period of the Mesozoic Era when large dinosaurs were
widespread