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The Universe • Earth is a part of a larger physical system that contains other planets, moons, and stars. This system is called the Universe. The Universe contains billions of galaxies, each with billions of stars. Many stars have their own system of planets, moons, and other orbital bodies. • Our galaxy is called the Milky Way. Earth is part of a solar system within the Milky Way. Our solar system revolves around our star, the Sun.
Our Solar System • Our solar system is made up of the Sun and other objects that revolve around it.
The Sun • Stars are giant balls of burning gases. Our Sun is a medium-sized star. Its enormous mass creates a strong gravitational pull which keeps the earth and other objects revolving around it.
The Planets • Planets—There are eight planets that revolve around the Sun. The inner planets are Mercury, Venus, Earth, and Mars. These are the terrestrial planets. The outer planets are Jupiter, Saturn, Uranus, and Neptune. These are called gas giants.
Moons—Planets have natural satellites called moons. We have one moon. Jupiter has the most with 63. Not all moons are like ours. Some have atmospheres. Others are irregular in shape, similar to asteroids.
Dwarf Planets—Small round bodies that orbit the Sun but have not cleared their orbits of other bodies are called dwarf planets. The largest dwarf planets are Pluto, whose orbit is beyond Neptune, and Ceres, whose orbit lies between Mars and Jupiter.
Asteroids, Comets and Meteoroids • Asteroids—small irregularly shaped planet-like objects; most are found in the asteroid belt between Mars and Jupiter • Comets—icy dust particles & frozen gases with long feathery tails; they have irregular orbits which cross planetary orbits • Meteoroids—chunks of rock and iron; some enter Earth’s atmosphere; those that impact the Earth are called meteorites; mostly insignificant, though some have caused catastrophic damage
Earth • The Earth is a rounded object, wider when measured at the Equator than from pole to pole. The Earth’s diameter is 7,930 miles, and its circumference is 24,900 miles. • Earth is the largest of the inner planets.
The Earth is composed of: • Water—about 70% of the Earth’s surface is covered by water—oceans, lakes, rivers, and other bodies of water. • Land—about 30% of the Earth’s surface is land. • Air—the layer of gases above Earth’s surface is made up of nitrogen (78%), oxygen (21%), and other gases • All life exists on or near the surface of the Earth.
Landforms—different shapes and elevations of land and undersea surfaces make up Earth’s landforms. Some are directly connected above water, others stand alone as islands. • From the shore, the land extends out from the coastal plain to form the continental shelf. This leads to the continental slope, which is a sharp drop-off of the continental shelf. This in turn leads to the ocean floor.
Landforms • Some common examples of landforms are: • mountain • valley • river • cape • bay • gulf Name ten other types of landforms.
Earth’s Extreme Landforms • Mount Everest is the Earth’s tallest peak, standing 29,028 feet above sea level. • The shore of the Dead Sea lies 1,349 feet below sea level, making it the lowest area of dry land on the planet. • At 35,827 feet below sea level, the Mariana Trench is the deepest spot on the globe.
Earth’s Structure • Core—made of iron and nickel the solid inner core is surrounded by an outer liquid core. The core is under enormous pressure. • Mantle—thick layer of hot, dense rock • Crust—rocky shell that forms the Earth’s surface. It ranges from 2 to 75 miles thick and is composed of more than a dozen movable plates.
Seismic Activity Seismic activity—earthquakes and volcanic eruptions—happens everyday. Recent Seismic Activity
Tectonic Plates • The earth’s surface is composed of about a dozen tectonic plates that are in motion against each other. Over millions of years, their movement has produced the landforms and bodies of water that we know today.
Plate Movement • Continental drift—theory that the continents were once joined and have slowly drifted apart • Plate tectonics—physical processes that have created many of the Earth’s physical features. Plates are constantly moving and, over millions of years, form mountains, create volcanoes, and produce earthquakes. • Magma—molten rock. Magma is pushed up from the mantle when plates separate.
Subduction—occurs when a heavier sea plate collides with a continental plate and is thrust downward. Then magma bursts through and creates volcanic mountains. • Accretion—occurs when a continental plate slides over a sea plate, leveling underwater features and expanding the continental land mass. • Spreading—occurs when sea plates pull apart and magma flows upward creating undersea volcanic mountains, ridges, and sometimes islands.
Folds and Faults • Folds—occur when plates push against each other and cause the Earth’s surface to buckle. This process causes folds, or bends, in layers of rock. • Faults—created when plates slide or grind past each other causing cracks in the Earth’s surface.
Earthquakes—sudden and violent movements of tectonic plates along a fault line. • Volcanic eruptions—periodic expulsion of magma between plates, causing eruptions of gas, ash, and lava.
External Forces of Change • Weathering—breaking down rocks • Physical erosion—large rock masses are broken down by physical actions • Chemical erosion—large rock masses are broken down by chemical changes in their composition
Erosion—wearing away the Earth’s surface • Wind erosion—movement of dust, sand, and soil from one place to another • Glacial erosion—movement of rocks and soil by the slow, gradual changes in glaciers • Water erosion—continual movement of soil and rocks by water slowly erodes surfaces, creating/modifying valleys, canyons, shorelines
Earth’s Water • Earth’s water resources are constant—the amount of water on our planet does not change. • Water cycle—the regular movement of water from ocean to air to land and finally back to ocean
Evaporation—the changing of liquid water into vapor, or gas, by the sun’s energy • Condensation—liquid water created when water vapor cools • Precipitation—moisture such as rain, sleet, or snow released from clouds
Bodies of Water • Salt water • Oceans—about 97% of the Earth’s water is salt water found in oceans, seas, and gulfs • Five principal oceans • Pacific (largest) • Atlantic • Indian • Arctic • Southern
Freshwater • Rivers, lakes & streams—about 3% of our planet’s water supply is freshwater; more than 2% is locked in ice. Less than 1% of Earth’s water is found in lakes, rivers and streams. • Groundwater—freshwater that lies beneath the Earth’s surface • Aquifer—a porous underground layer of rock saturated by very slow flows of water
