Download Learn about how climate change affected life on Earth. See the

Learn about how climate
change affected life on
Earth. See the video
“Noah’s Snowball.”
446 Unit 4: Life Over Time
Climate and Life
Throughout its history, Earth’s climate has changed many times.
Often the changes are gradual. They may seem small. However, an
average global temperature change of just a few degrees can have
a large impact on climate. Small changes in climate then cause big
changes for plants and animals.
Before there were humans to record events,
Earth recorded its changes in its rocks and fossils. For
example, scientists get a sense for Earth’s climate at
different times in the distant past by looking at fossils,
the remains and traces of living things. If scientists
find fossils of tropical plants in places near the arctic
circle, then they may conclude that the climate in
those places was different in the past.
Scientists have found that warmer climates lead to a greater
diversity of organisms. One researcher examined fossils of tiny
organisms called phytoplankton (FY-toh-PLANK-tuhn). During
cooler climate periods, there were fewer types of phytoplankton
than during warmer periods. The same is true for other organisms.
Peter Wilf and Conrad Labandeira studied fossil plants. They were
especially interested in the marks they found on the plants. The
marks were left by plant-eating animals who bit the leaves. The
warmer the climate was, the more types of plants there were—and
the more kinds of animals were eating the plants.
SOURCE: Images © 2000 AAAS
The chew marks of the hispine beetle larva on living ginger in Panama (left)
look similar to fossilized chew marks found in Wyoming (three photos right).
Frontiers in Science 447
Before and after photographs of the sky show that distinct bands appeared due to dust and
ash from the 1991 volcanic eruption of Mt. Pinatubo.
Mass Extinction
Turn of Events
Several times in Earth’s past, many kinds of animals and plants have disappeared in a relatively
short time. These events are called mass
extinctions. While we don’t know for sure what
causes them, most scientists think climate change
plays a role in mass extinctions.
What caused this extinction? Using fossils, scientists have concluded that Earth’s climate became
cooler. Material from erupting volcanoes may
have blocked sunlight long enough to cool the
Earth. The cool temperatures and lack of sunlight
may have killed plants and animals.
The largest mass extinction in Earth’s history
happened at the end of the Permian (PER-meeuhn) Period about 248 million years ago.
Scientists estimate that 90–95 percent of animal
species that lived in the water died out. About
three quarters of the vertebrates, or animals with
backbones, living on land died out too.
Scientist Peter Ward has been studying the
Permian extinction. He looked at ancient African
rivers and found evidence that rivers had became
clogged with soil. Plants normally holding soil in
place may have been wiped out, causing the soil
on the riverbanks to loosen. The plant extinction
would also have led to animal extinction.
View the “Noah’s Snowball” segment of your Scientific American
Frontiers video to learn about
another theory of how climate
change affected life on Earth.
IN THIS SCENE FROM THE VIDEO
Fossil hunters examine evidence
of early life in China.
DEEP FREEZE Can you imagine what Earth would
be like if it were completely covered in ice?
Geologists Paul Hoffman and Dan Schrag suggest
Earth was frozen solid until about 600 million
448 Unit 4: Life Over Time
years ago. They think
Earth’s climate changed by
just a few degrees, but it
was enough to make the
ice caps cover the planet.
The only life that survived
was bacteria that were
kept warm by volcanoes.
And it was the volcanoes
that changed the climate
again, say Hoffman and
Schrag. Suddenly eruptions
melted the ice. Ocean
levels rose. The scientists think this change might
have taken only a hundred years. Not everyone
agrees with the snowball hypothesis, but it could
explain why new forms of life began to appear.
What Hit Them?
Not all scientists agree about what caused the
Permian extinction. If an asteroid hit Earth, it
would push massive amounts of dirt and dust
into the air. This could block sunlight and create a
cooler climate. An increase in volcanic eruptions
is another possible cause.
The most famous extinction of all took place
at the end of the Cretaceous Period. The
extended winter that may have followed a
meteor impact caused many large land
animals—including dinosaurs—to become extinct.
In a new climate some species thrive and
survive. They spread out and, over time, evolve to
fill empty niches or unique roles in the
environment. For example, before the Cretaceous
extinction, the only mammals were small.
After the dinosaurs became extinct, large mammals could fill the roles of large plant-eaters and
meat-eaters.
Even today, climate change continues. Earth’s
average temperature rose about half a degree
Celsius in the twentieth
century. Studying how
past climate changes
shaped life helps scientists predict how it may
affect us in the future.
A large plant-eating
mammal, Chalicotherium
grande, roamed Asia
millions of years ago.
Scientists have learned a lot about climate
change and mass extinctions by studying fossils.
There are many questions still to be answered.
• What caused changes in Earth’s climate?
As you study this unit, work alone or
with a group on one of the projects
listed below. Use the bulleted steps to
guide your project.
Museum Display
What organisms survived the Permian
extinction? What organisms went
extinct?
• Create a museum display using art
and text.
• Use visuals to show the organisms and
the modern relatives that have close
connections to them.
Design a Robot
Often, scientists design robots to study
dangerous or distant locations.
• Design an artificial robot that would
be well-adapted to survive an event
that causes a mass extinction.
• Explain why the design would help the
robot remain in operation.
Species over Time
Find out more about species that have
gone extinct during recorded history.
• Choose one species that is now extinct.
• Present a timeline giving a history of
that species.
• Describe what some of its ancestors
and surviving related organisms are.
• Describe when it was last seen.
Include some of the possible
reasons for why it died out.
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• What else might have caused mass extinctions?
• How might climate change affect life on Earth
in the future?
Learn more about careers in
paleontology.
Frontiers in Science 449