Earth's Layers and Plate Tectonics

Earth's Layers and the Crust

• Earth's layers include the crust, mantle, outer core, and inner core.
• The crust is the outermost layer, making up continents and oceans.
• The crust is the thinnest layer.

Convection Currents

• Convection currents are caused by uneven temperatures within Earth.
• Hot rock rises, cools, and sinks, creating a circular pattern.
• These currents move tectonic plates.
• Convection currents are similar to boiling water, creating ridges and trenches.

Pangaea

• Pangaea was a supercontinent that existed 200 million years ago.
• It eventually broke apart and formed the continents we know today.
• Alfred Wegener proposed the idea of continental drift.
• Wegner's evidence of continental drift came from jigsaw puzzle fit of continents, ice sheets, fossils and mountain ranges.

Plate Tectonics

• Earth's outer shell is made of about 20 plates.
• These plates float on a layer of hot rock, several hundred kilometers beneath the surface.
• Plates move in three ways:
  • Divergent: Plates move apart, forming ridges (e.g., Mid-Atlantic Ridge).
  • Convergent: Plates move together, forming trenches, and continental plates go over oceanic plates (e.g., Pacific Coast).
  • Transformative: Plates slide past each other, causing earthquakes.

Mountain Formation

• Mountains are formed when continental and oceanic crust converge.
• Oceanic crust slides beneath the continental crust.

Natural Disasters

• Earthquakes occur when plates move but friction stops them, and they suddenly become unstuck.
• Tsunamis occur when earthquakes happen underwater, causing water to rise.
• Volcanoes form along plate boundaries where magma reaches the surface (e.g., Hawaiian Islands).

Subduction Zone

• A subduction zone is a tectonic feature where one tectonic plate slides under another at a converging plate boundary.

Geologic Eras

• Precambrian Era: 4 billion years, first single celled organisms.
• Paleozoic Era: 370 million years, first fish and land plants.
• Mesozoic Era: 165 million years, Dinosaurs.
• Cenozoic Era: 65 million years, modern humans developed.
• Precambrian is the longest era; Cenozoic is the shortest.

Formation of Landforms

• Canadian Shield and Appalachian Mountains formed during the Paleozoic era.
• Western Cordillera formed during the Mesozoic era.

Rock Cycle

• The rock cycle describes how rocks change from one form to another through various processes.
• Sedimentary rocks are formed from pre-existing rocks that have been broken down, transported, and deposited into layers.
• Metamorphic rocks are formed from other rocks that have been transformed by heat and pressure.
• Igneous rocks are formed from the cooling and hardening of magma.

Weathering and Erosion

• Weathering breaks down rocks into smaller pieces.
• Physical weathering changes physical structure of rocks.
• Chemical weathering changes the chemical composition of rocks.
• Erosion moves weathered material from one place to another.
• Agents of erosion include: water, ice, wind, and gravity

Glaciers

• Glaciers form when snow piles up and compresses into ice, moving downhill.
• Glaciers during the last ice age impacted Ontario's landscape by creating lakes, valleys, and shaping the land.
• Alpine glaciers form in mountains and move down valleys.
• Continental glaciers are large ice sheets that cover large land areas.