Our Changing World

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