1. Chapter 2 Earth and the Sun’s Energy
The Big Idea
Earth’s movement and the sun’s energy interact to create day and night, temperature changes, and the seasons.
Main Ideas
Earth’s movement affects the amount of energy we receive from the sun.
Earth’s seasons are caused by the planet’s tilt.

2. Earth’s movement affects the amount of energy we receive from the sun.
All life on Earth requires solar energy, or energy from the sun, to survive.
Amount of solar energy received changes constantly
Earth’s rotation, revolution, tilt, and latitude all affect the amount of solar energy Earth receives.

4. Rotation
Earth spins on its axis —an imaginary line that runs through the center of the planet around which it turns.
It takes Earth 24 hours to make one rotation, or complete spin on its axis.
As Earth spins, different parts of the planet face the sun, thus causing the changes from day to night.

5. Revolution Earth follows an orbit, or path, around the sun.
Orbit is not a perfect circle.
It takes Earth 365¼ days to complete one revolution, or trip around the sun.
Our calendar year is based on the time it takes Earth to complete its orbit.

6. Tilt
Tilt
Earth’s axis is tilted at an angle of 23½ degrees from vertical.
At any give time of year, some places on Earth tilt toward the sun, and others tilt away.
Places tilting toward the sun receive more solar energy and have warmer temperatures than those that tilt away.

7. Latitude
Latitude
Latitude is the distance north or south of Earth’s equator.
Low-latitude areas, those nearest the equator, receive direct rays from the sun all year.
High-latitude areas, those farther from the equator, receive indirect rays from the sun and have colder temperatures.

8. Questions of the Day What is solar energy?
How does the Sun affect life on Earth?
What four things affect the amount of sunlight we receive?
Take the next 5 minutes in class to answer these questions.
Refer back to your notes for help!

9. Earth’s seasons are caused by the planet’s tilt.
Seasons are periods during the year that are known for a particular type of weather.
Many places experience four seasons: winter, spring, summer, and fall.
In some parts of the world, seasons are based on the amount of rainfall
Earth’s seasons are caused by the planet’s tilt.

11. Summer
Earth tilts towards the sun in summer.

12. Winter
Earth tilts away from sun in winter

13. Spring and Fall
In spring: tilt toward sun, solar energy increases, temperatures rise, and days grow longer.
In fall: tilts away from sun, solar energy decreases, temperatures decrease, days are shorter

14. Tropics
Tropics: seasons are marked by rainfall rather than temperature.
Monsoons, winds bring either dry or moist air to the tropics, creating wet and dry seasons.

16. The Seasons
Winter and Summer
Earth tilts away from sun in winter and towards the sun in summer.
Because of the Earth’s tilt, the Northern and Southern hemispheres experience opposite seasons.
Spring and Fall
In spring, Earth begins to tilt toward sun, solar energy increases, temperatures rise, and days grow longer.
In fall, the opposite occurs.
Rainfall and Seasons
In the tropics, regions close to the equator, seasons are marked by rainfall rather than temperature.
At certain times of year, winds bring either dry or moist air to the tropics, creating wet and dry seasons.

17. Water on Earth
Water is a dominant feature on Earth’s surface and is essential for life.
Salt water and freshwater make up Earth’s water supply.
In the water cycle, water circulates from Earth’s surface to the atmosphere and back again.
Water plays an important role in people’s lives.

18. Salt water and freshwater make up Earth’s water supply.
Water covers some two-thirds of the planet.
Earth’s Water
About 97 percent of the Earth’s water
Unsafe to drink because of high levels of salt
In general, found in Earth’s oceans, which cover some 71 percent of the planet’s surface
Also found in some of Earth’s lakes
Salt Water
Water without salt
Makes up only 3 percent of our water supply
Freshwater

19. Freshwater
Much of Earth’s freshwater is locked in glaciers, large areas of slow moving ice, and in the ice of the Arctic and Antarctic regions.
Surface water is water that is found in Earth’s streams, rivers, and lakes.
Less than one percent of Earth’s water supply
Streams, rivers, and lakes are common sources.
Precipitation is water that falls to Earth’s surface as rain, snow, sleet, or hail.
Most available freshwater is groundwater, water found below Earth’s surface.
Some naturally bubbles from the ground to the surface as a spring.
Most obtained by digging wells

20. The Water Cycle
Water is the only substance on Earth that occurs naturally as a solid, a liquid, and a gas, or water vapor.
The water cycle is the movement of water from Earth’s surface to the atmosphere and back ; it is driven by the sun’s energy.
Evaporation—water turns from liquid to gas.
Condensation —the rising gas cools and condenses, or changes from a vapor into tiny liquid droplets, to form clouds.
Precipitation —if the droplets in clouds become heavy enough, they fall back to Earth as rain, snow, sleet, or hail.
Runoff —excess water that isn’t absorbed as groundwater flows over land and collects in streams, rivers, and oceans.

22. Water plays an important role in people’s lives.
Water Problems
Lack of available freshwater, which can be caused by droughts or overuse
Contaminated, or polluted, water can harm humans, plants, and animals.
Flooding can damage property and threaten lives.
Water Benefits
Provides us with food to eat
Important source of energy
Provides us with recreation, including swimming, fishing, surfing, and sailing

23. The Land
Processes below and on Earth’s surface shape the planet’s physical features.
Earth’s surface is covered by many different landforms.
Forces below Earth’s surface build up our landforms.
Forces on the planet’s surface shape Earth’s landforms.
Landforms influence people’s lives and culture.

24. Earth’s surface is covered by many different landforms.
Landforms, or shapes on the planet’s surface, make up the landscapes that surround us.
Earth’s surface is covered with landforms of many different shapes and sizes.
Mountains, land that rises higher than 2,000 feet
Valleys, areas of low land located between mountains or hills
Plains, stretches of mostly flat land
Islands, areas of land completely surrounded by water
Peninsulas, land surrounded by water on three sides

25. Forces below Earth’s surface build up our landforms.
Earth’s Plates
The planet’s continents, or large landmasses, are part of Earth’s crust—the solid outer layer of the planet.
Theory of plate tectonics suggests that Earth’s surface is divided into a dozen or so slow-moving plates, or pieces of Earth’s crust.
Movement of Continents
The idea that continents have traveled great distances over millions of years is known as continental drift.
Theory, developed by Alfred Wegener, states that the continents were once united in a single supercontinent and over time, slowly separated and moved to their present positions.
As plates collide, separate, and slide, they shape Earth’s landforms

26. Plates Collide, Separate, and Slide
Two ocean plates: one pushes under the other, creating ocean trenches, or deep valleys in ocean floor
Ocean and continental plate: ocean plate drops beneath continental plate, forcing land above to crumple and form mountain range
Two continental plates: land pushes up to form mountains
Plates Separate
As plates move apart, gaps between plates allow magma to rise to Earth’s crust.
Lava, magma that reaches the Earth’s surface, emerges from the gap.
As lava cools, it builds a mid-ocean range, or underwater mountain, that can rise above the surface of the ocean to form islands.
Plates Slide
As plates pass by each other, they sometimes grind together, producing earthquakes, sudden, violent movements of Earth’s crust.
Earthquakes often take place along faults, or breaks in Earth’s crust where movement occurs.
The region around the Pacific plate, called the Ring of Fire, is home to most of the world’s earthquakes and volcanoes.

30. Forces on the planet’s surface shape Earth’s landforms.
Weather, water, and other forces change Earth’s landforms by wearing them away or reshaping them.
Weathering is the process by which rock is broken down into smaller pieces called sediment.
Heating and cooling can cause rocks to crack.
Expansion of water as it freezes can cause cracks to expand.
Roots of trees can pry rocks apart.
Erosion is the movement of sediment from one location to another.
Can wear away or build up landforms

31. Types of Erosion Wind Erosion Glacial Erosion Water Erosion
Winds lift sediment into air and carry it across great distances .
On beaches and in deserts, deposits can form dunes.
Blowing sand can wear down rock.
Glacial Erosion
Glaciers, or large, slow-moving sheets of ice, erode the land by carving valleys and mountain peaks.
Crush rock into sediment and move it great distances
Water Erosion
Waves and flowing water can cut through rock, carry sediment, and deposit sediment in new locations.
Floodplains are created when rivers flood their banks and deposit sediment.
Sediment carried by a river all the way to the sea creates a delta.