1. Our Changing World
2.5

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. Vocabulary
Pangaea
Ice Age
Glacier
Sedimentary Rock
Fossil
Proxy Data