Chapter 2 “CLIMATE" GEO SKILLS

Earth and the Sun’s Energy A. The Earth’s tilt and rotation affect the amount of energy we receive from the sun. It takes 24 hours for Earth to spin on its axis. As Earth rotates on its axis, energy from the sun creates periods of day and night. The half of the planet that faces the sun during this period experiences daytime, and it experiences night when it turns away from the sun.

Earth and the Sun’s Energy B. As the Earth spins on its axis, it also follows a path, or orbit, around the sun. Since the orbit is not a perfect circle, it sometimes takes the Earth closer to the sun or further away. It takes 365 ¼ days for the Earth to complete one revolution, or trip around the sun.

The Seasons: Northern Hemisphere As Earth orbits the sun, the tilt of its axis toward and away from the sun causes the seasons to change. Seasons in the Northern Hemisphere change at about the same time every year.

The Seasons Winter and Spring The North Pole tilts away from the sun in winter, causing cooler temperatures. In the spring, temperatures gradually rise as the North Pole begins to point toward the sun. The Seasons Spring March 21 Winter December 21 Summer June 21 Fall September 22 Summer and Fall Summer’s warm temperatures are the result of the North Pole’s tilt toward the sun. As we move away from the sun in the fall, temperatures slowly decline. The Tropics Some regions on Earth have seasons marked by rainfall rather than temperatures. This is true in the tropics, regions close to the equator. At certain times of the year, winds bring either dry or moist air to the tropics, creating wet and dry seasons.

Earth’s Orbit and Seasons

Water on Earth I. Earth’s Water Supply Water covers two-thirds of the Earth’s surface. Salt Water – Oceans hold 97 percent of Earth’s water supply. Because salt water contains high levels of salt and other minerals, it is unsafe to drink. Fresh Water – or water without salt, makes up only about 3 percent of our total water supply. Much of that freshwater is locked in Earth’s glaciers, large areas of slow-moving ice, and in the ice of the Antarctic and Arctic regions. Surface water is water that is found in Earth’s streams, rivers, and lakes. Water found below Earth’s surface is called groundwater. Aquifers are rock layers that hold large amounts of fresh water below the surface.

Water on Earth II. The Water Cycle The water cycle is the movement of water from Earth’s surface to the atmosphere and back. As the sun heats water on Earth’s surface, some of that water evaporates, or turns from liquid to gas, or water vapor. Cooling causes the water vapor to condense, or change from a vapor into tiny liquid droplets. If the droplets become heavy enough, precipitation occurs – that is, the water falls back to Earth as rain, snow, sleet, or hail.

Earth’s Plates Earth’s Plates – The planet’s continents, or large landmasses, are part of Earth’s crust. The 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. As plates collide, the energy created from their collision produces distinct landforms. When two ocean plates collide, one plate pushes under the other. This process creates ocean trenches. The collision of two continental plates also results in mountain- building. When continental plates collide, the land pushes up, sometimes to great heights.

Earth’s Plates B. A second type of plate movement causes plates to separate. As plates move apart, gaps between the plates allow magma, a liquid rock from the planet’s interior, to rise to Earth’s crust. As the lava cools, it builds a mid-ocean ridge, or underwater mountain. Volcanoes and geysers are part of the Earth’s process of releasing pressure as plates separate. C. Tectonic plates also slide past each other. This grinding produces earthquakes – sudden, violent movements of Earth’s crust. Earthquakes often take place along faults, or breaks in Earth’s crust. The Ring of Fire is home to most of the world’s earthquakes and volcanoes.