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 Pangaea Ice Age Glacier Sedimentary Rock Fossil Proxy Data