Download Our Changing World

Our Changing World
2.5
Our Changing World
• Earth’s daily rotation is easily visible in the light
• Weather changes are obvious with lightning and
snow/rain
• Water cycle can be seen in action (evaporation,
condensation, cloud formation, etc.)
• Some of the biggest changes are happening so
slowly that humans may never see them
Changes in the Earth
• Moving plates have kept the Earth’s surface in a
constant state of change
• Over 200 million years ago, Earth had a single
landmass called Pangaea
• Plate movement caused the landmass to break
apart
Changes
• Plate movement continues to change the
position of continents and ocean borders
• People cannot see this movement, but we can
measure it
• Rocky Mountains: stopped rising after shock
waves stopped pushing the rock formations up
• Half their height due to erosion
Global Climate
• For most of Earth’s history, temps have been
5◦C-8◦C warmer than they are today
• About 925 million years ago, periods of severe
cold began known as ice ages
• Ice ages produce enormous ice sheets known as
glaciers across most of the planet
Climate Change
• 18,000 years ago, nearly 1/3 of Earth’s land was
covered with ice
• The ice sheets altered the landscape by carving
out hills and valleys, eventually melting to form
lakes
• Greatly affects species in the area and how they
can thrive
Measuring Change
• Earth has existed much longer than people have
been writing about it
• Rocks provide the best record of Earth’s history
• Most rocks form in layers as bits of gravel, sand,
and mud pressed together
• These are known as sedimentary rocks
• These preserve a rough record of the past
Fossils
• Sometimes sedimentary materials trap living
and dead animals and plants
• These preserved traces or remains are called
fossils
• Fossils can show that animals from northern
areas lived in southern areas during a past ice
age
• Rocks can provide fossil evidence of Earth’s past
climate
Proxy Data
• Fossilized evidence that helps scientists
understand past climate conditions
▫ Cross section of rings in a tree trunk show growth
▫ The width of rings show warm, wet, dry or cold
▫ Growth rate of coral reefs reflect climate
conditions
▫ Trapped air (bubbles) in glaciers are analyzed by
scientists to learn what the atmosphere was like
Looking Ahead
• Studying Earth’s physical history teaches people
many things
▫ shows when and how Earth’s land, air, and water
have changed
▫ Shows the impact these changes have had on
Earth’s life forms
Humans are now a major force shaping life on Earth
Vocabulary
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Pangaea
Ice Age
Glacier
Sedimentary Rock
Fossil
Proxy Data