Table of Contents
Earth's Layers
Earth is made up of four main layers, each with different properties and composition.
1. Crust (0-70 km)
The thin, outer layer where we live.
- • Made of rocks and minerals
- • Continental crust: Land (thicker, 35-70 km)
- • Oceanic crust: Under oceans (thinner, 5-10 km)
2. Mantle (70-2,900 km)
The thickest layer, very hot.
- • Made of hot, dense rock
- • Upper mantle: Semi-solid, moves slowly
- • Lower mantle: More solid, hotter
- • Convection currents cause tectonic plates to move
3. Outer Core (2,900-5,150 km)
Liquid metal layer.
- • Made of liquid iron and nickel
- • Temperature: 4,000-6,000°C
- • Creates Earth's magnetic field
4. Inner Core (5,150-6,370 km)
The hottest, solid center.
- • Made of solid iron and nickel
- • Temperature: Up to 6,000°C (as hot as the sun's surface!)
- • Solid because of extreme pressure
Remember: "Cold Makes Others Icy"
Crust → Mantle → Outer Core → Inner Core
Types of Rocks
There are three main types of rocks, classified by how they are formed.
Igneous Rocks
Formed by: Cooling of hot magma or lava
"Igneous" comes from "ignis" (Latin for fire)
Examples:
- • Granite (cools slowly underground)
- • Basalt (cools quickly above ground)
- • Obsidian (volcanic glass)
Sedimentary Rocks
Formed by: Layers of sediment pressed together
Often contain fossils
Examples:
- • Limestone (from shells/coral)
- • Sandstone (from sand)
- • Shale (from mud/clay)
Metamorphic Rocks
Formed by: Heat and pressure changing existing rocks
"Metamorphic" means "change form"
Examples:
- • Marble (from limestone)
- • Slate (from shale)
- • Quartzite (from sandstone)
The Rock Cycle
The rock cycle shows how rocks change from one type to another over millions of years.
From magma/lava
From layers
Changed form
Hot liquid rock
Processes in the Rock Cycle
Weathering
Breaking down of rocks by wind, water, ice, or plants
Erosion
Moving rock pieces from one place to another
Deposition
Dropping and settling of sediments
Compaction
Layers pressing together to form rock
The Water Cycle
The water cycle is the continuous movement of water between Earth's surface and the atmosphere.
Evaporation
Sun heats water → water vapor rises
Condensation
Water vapor cools → forms clouds
Precipitation
Water falls as rain, snow, sleet, or hail
Collection
Water gathers in oceans, lakes, rivers
Additional Processes
Transpiration
Plants release water vapor through their leaves
Runoff
Water flows downhill on land's surface to streams and rivers
Infiltration
Water seeps into the ground to become groundwater
Groundwater
Water stored underground in rocks and soil
Ecosystems
An ecosystem is a community of living things (organisms) interacting with each other and their non-living environment.
Biotic Factors (Living)
- • Plants (trees, grass, flowers)
- • Animals (mammals, birds, insects)
- • Microorganisms (bacteria, fungi)
- • Decomposers (worms, mushrooms)
Abiotic Factors (Non-living)
- • Sunlight
- • Water
- • Air (oxygen, carbon dioxide)
- • Soil/rocks
- • Temperature
Types of Ecosystems
Forest
Rainforest, temperate forest
Desert
Sahara, Gobi
Grassland
Savanna, prairies
Ocean
Coral reefs, deep sea
Freshwater
Rivers, lakes, ponds
Tundra
Arctic, alpine
Wetlands
Marshes, swamps
Urban
Cities, parks
Food Chains & Food Webs
Food Chain
A food chain shows a single pathway of how energy flows from one organism to another.
Sun
Energy source
Producer
Makes food
Primary Consumer
Herbivore
Secondary Consumer
Carnivore
Tertiary Consumer
Top predator
Energy Pyramid
Only about 10% of energy is passed to the next level. The rest is lost as heat.
Food Web
A food web shows many connected food chains in an ecosystem. It's more realistic because animals eat more than one type of food.
Example: A hawk might eat snakes, mice, and rabbits. A rabbit eats grass and leaves. A mouse eats seeds and insects. All these connections form a food web.
Forms of Energy
Energy is the ability to do work or cause change. It cannot be created or destroyed, only transformed.
Light Energy
Energy we can see. Comes from the sun, light bulbs, fire.
Heat Energy (Thermal)
Energy from temperature. Moves from hot to cold objects.
Sound Energy
Energy from vibrations traveling through air, water, or solids.
Electrical Energy
Energy from moving electrons. Powers our devices.
Mechanical Energy
Energy of motion (kinetic) and position (potential).
Chemical Energy
Energy stored in food, fuel, and batteries.
Energy Transformation Examples
Light bulb: Electrical → Light + Heat
Car: Chemical (fuel) → Mechanical (motion)
Solar panel: Light → Electrical
Eating food: Chemical → Mechanical + Heat
Simple Circuits
A circuit is a complete path that allows electricity to flow. For electricity to flow, the circuit must be closed (complete).
Parts of a Circuit
Power Source
Provides energy (battery, outlet)
Wires
Conductors that carry electricity
Load
Device that uses electricity (light, motor)
Switch
Opens/closes circuit (on/off)
Types of Circuits
Series Circuit
One path for electricity. All components in a line.
If one bulb burns out, ALL go out!
Parallel Circuit
Multiple paths for electricity. Components on separate branches.
If one bulb burns out, others stay on!
↓→💡
↓→💡→🔋
Conductors vs. Insulators
Conductors
Allow electricity to flow easily
Examples: metals (copper, iron), water
Insulators
Block or slow down electricity
Examples: rubber, plastic, wood, glass