II. Geosciences Review

ASTRONOMY

Astronomy is the study of space and the relationship of objects in space. Astronomers use optical telescopes and radio telescopes, including the orbiting Hubble Telescope, to study space and objects in space. Our solar system has one star (the sun), nine planets, some comets, and lots of satellites (moons), asteroids, and meteors. Our sun is a star, a turbulent mass of incredibly hot gases exploding with repeated nuclear fusion reactions. Without the heat and light from the sun, our universe would not exist as we know it. About 1,000,000 earths could fit inside the sun. The sun’s diameter is about 864,000 miles, and the surface temperature is over 10,000° Fahrenheit. Still, the sun is just average size by galactic standards.

The sun is at the center of our solar system, although this was not realized until the time of Copernicus in the 1500s. The most noticeable features of the sun’s surface are the sunspots, cooler areas that move across the sun’s surface. Sunspots appear in somewhat predictable cycles and are associated with interruptions in radio and television transmissions. Earth is the name of our planet. The earth is the third planet from the sun. The earth’s distance from the sun ranges from about 91,000,000 to 95,000,000 miles. It takes light about eight minutes to travel from the sun to earth. The earth’s diameter is about 7,900 miles. The earth’s rotation and revolution have a tremendous impact on life here.

The earth rotates around its axis, which roughly runs through the geographic north and south poles. This rotation creates day and night as parts of the earth are turned toward and then away from the sun. The earth revolves in an orbit (path) around the sun. The earth’s axis is tilted about 23° from perpendicular with the orbit around the sun. The tilting and revolving creates seasons as regions of the earth are tilted toward the sun and away from the sun.

Moon is the name for the satellite that revolves around earth. The moon also rotates around its axis. The moon’s diameter is about 2,100 miles and it is about 240,000 miles from the earth to the moon. The moon has no atmosphere and its surface is covered with craters from meteorites and from volcanoes.

The moon’s rotation and revolution each take about 27 1/2 days. These equal periods of rotation and revolution mean that the same part of the moon always faces the earth. It was not until lunar exploration in the 1970s that the other side of the moon was viewed and photogaphed. Different parts of the moon’s surface reflect light to the earth, creating the different phases of the moons.

The phases of the moon are also integrally related to tides on earth. High tides occur on the parts of earth directly under the moon and on the other side of earth directly opposite this point. Low tides occur halfway between the two high tides. The tides move around the earth as the moon revolves around the earth, creating two high and two low tides each day at each place on earth. The lowest and highest tides occur when the sun and the moon are in a straight line. These tides are called spring tides. The moon is either new or full during this direct alignment.

The position of the sun, earth, and moon can create eclipses. A lunar eclipse occurs when the moon is in the earth’s shadow. A solar eclipse occurs when the sun is “hidden” behind the moon.

The word planet comes from the Latin word meaning traveler. Ancient observers were taken by the “lights” they saw traveling around the sky against a background of other “lights” that seemed stationary. Today we know that nine planets including earth travel in orbits around the sun. Also in orbit around the sun are a belt of asteroids from 1 to 500 miles in diameter that may be the remains of an exploded planet.

Cosmology is the study of the universe. Cosmological theories are about the origin, development, and ultimate fate of the universe. The universe consists of a large number of galaxies that contain an enormous number of stars and other material. Our solar system is located on the outer edge of the Milky Way galaxy. All the stars you can see from earth without a telescope are in the Milky Way galaxy. Intergalactic distances are so huge that they are measured in light years. Light travels about 6 trillion miles in a year. It takes light 300 years to travel from Polaris, the North Star, to earth. It would take about 100,000 years for light to travel across the Milky Way galaxy. Scientists have discovered a great many other galaxies. The Andromeda galaxy is over 2 million light years away from earth. The most distant detectable galaxies are about 10 to 16 billion light years from earth. Scientists have discovered that galaxies are moving away from each other. This, among other factors, has led most scientists to embrace the Big Bang theory. This theory proposes that helium and hydrogen combined to create a gigantic explosion 16 billion to 20 billion years ago. This explosion led to the development of the stars, galaxies, and eventually planets.

METEOROLOGY

Meteorology is the study of the earth’s atmosphere. Weather observations are taken on the ground, in the upper atmosphere, and from satellites in space. All these observations inform us about likely weather events and add to our knowledge about the atmosphere. The complex movement of air masses creates our weather. This movement begins because air around the equator is heated and air at the poles is cool. Air in the lower atmosphere moves toward the equator, while upper air moves toward the poles. High pressure systems are usually associated with good weather. Wind circulates to the right around a high pressure system. Low pressure systems are usually associated with bad weather. Wind circulates to the left around a low pressure system.

Humidity refers to the percent of water vapor in the air. Dew point is the temperature below which the air will become so humid that it is saturated with water. Humidity above 60 or 65 percent makes us more uncomfortable because perspiration evaporates slowly. When the temperature is below the dew point, the air is saturated with water droplets or ice crystals, and fog or clouds are formed. Fog is a cloud that touches the ground. Clouds are formed well above the ground.

Stratus clouds refer to low-hanging clouds. Rain or snow may fall from nimbostratus clouds. Other stratus clouds can appear after rain has fallen. Stratus clouds may be just a few thousand feet above the ground. Cumulus can be puffy cotton-like clouds that appear in the afternoon. The base of these clouds is about a mile above the ground. Cumulonimbus clouds are huge dark cumulus clouds that produce thunderstorms and hail. All cumulus clouds have strong convective, upward wind currents. Cirrus clouds are high wispy clouds made up of ice crystals. Cirrus clouds are frequently three to five miles above the ground.

When condensed water or ice crystals become too dense for the air to support the precipitate, they fall toward the ground. Rain is water droplets that fall to the ground. Snow crystallizes from water droplets in clouds and falls to the earth. Sleet begins as rain and freezes or partially freezes as it falls to the earth. Freezing rain is rain that freezes when it strikes the surface. Hail is rain that freezes in cumulonimbus clouds and is blown up and falls only to be blown up again. This cycle is repeated many times, forming noticeable layers of ice in a hailstone.

Lightning is an instantaneous, high energy electrical discharge in the atmosphere. Lightning occurs when positive and negative charges are separated in the atmosphere. While this occurs most often in violent thunderstorms it can occur also in sandstorms or in clouds above volcanoes. Lightning can be from cloud to cloud, or from cloud to ground.

Weather maps show the position of pressure systems and fronts. A warm front signals that the air behind the front is warmer than the air in front. A cold front signals that the air behind the front is colder.

Oceanography is the study of the world’s oceans and ocean beds. Oceanographers are concerned with 71 percent of the earth’s surface. The ocean floor is covered by sediment, which reveals information about life on earth. Midocean ridges are the source of many volcanic eruptions. Seawater itself is about 3. 5 percent salt. Ocean currents, such as the Gulf Stream, are like rivers of water within the ocean. The sea provides over one-quarter of the protein needed in the world. Off-shore wells provide about 15 percent of the world’s petroleum. Pollution by petroleum spills and other factors has had a noticeable impact on the oceans and on marine life.

GEOLOGY

Geology is the study of the earth, its development and origin. The earth has five parts—atmosphere, crust, mantle, outer core, and inner core. The atmosphere is the gaseous region that surrounds the earth; it consists of 78 percent nitrogen and 21 percent oxygen. The remaining 1 percent consists of carbon dioxide, argon, water vapor, and other gases. The atmosphere extends out about 650 miles. But air becomes thinner as you travel away from earth and only the bottom 3 1/2 miles or so of the atmosphere is habitable by humans without special equipment. The ozone layer, which protects earth from ultraviolet rays, is about 20 miles up.

The hydrosphere is the layer of water that covers about three-quarters of earth’s surface. Ocean water, salt water, makes up about 95 percent of all earth’s water. Oceans average about 12,400 feet deep. Below 100 feet, water temperature decreases rapidly. At 5,000 feet, the ocean temperature is near freezing.

The lithosphere includes the rigid crust (20 miles thick) and upper mantle (40 miles thick) of the earth. The lithosphere is divided into a number of tectonic plates, which drift across earth’s surface on the partially molten asthenosphere. The asthenosphere separates the lithos­phere from the mantle. The rigid mantle reaches to a depth of about 1,800 miles. The outer core is about 1,400 miles thick and consists of dense rigid materials. The inner core has a radius of about 800 miles and is very dense and hot with temperatures over 10,000°F. The heat generated in the inner core is transferred to the surface and provides the energy for continental drift and for molten rock, which erupts on land and in the ocean.

Geologists study rocks. Three types of rocks are found in the earth’s crust — sedimentary, igneous, and metamorphic. Sedimentary rocks form in water when sediments and remains of dead organisms harden. Igneous rocks form when molten rock, magma, crystallizes. Metamorphic rocks form when other rocks are subjected to extreme pressure. Sedimentary rocks are found near the surface of the earth while igneous and metamorphic rocks are usually found beneath the surface.

Fossils are evidence of living organisms. Geologists and other scientists use fossils to learn about earth’s history. Fossils usually form when organisms die and are buried in the sediment that forms sedimentary rocks. Other fossils include footprints or tracks of animals. Fossils of animals help us date rocks and other layers of the earth.

Geologic processes can be external and internal. As new rocks are being created, old ones are being destroyed, and earth’s surface is being worn away. This process is called erosion. Most erosion begins with weathering. Weathering disintegrates rocks physically and chemically. Physical weathering breaks up rocks and may be caused by intense heat or cold, by frost, or by the action of vines or the roots of plants. Chemical weathering changes the composition of the rocks. Rain water combines with small amounts of carbon dioxide in the atmosphere to form carbonic acid, which can dissolve or decompose minerals. Streams, rivers, and wind erode rocks and carry away soil, while glaciers can gouge out huge grooves in rocks and in the soil. Beaches are the result of erosion from the pounding surf or oceans. Humans cause erosion. The earth’s interior is very hot. Holes drilled one mile into the earth can be 85° to 90° warmer at the bottom than on the surface. This is why geologists believe that the interior of the earth, which extends down almost 4,000 feet, is exceptionally hot. This belief is bolstered by the molten rock that erupts from volcanoes and by the boiling water in springs at the earth’s surface.

New mountains and land are constantly being created. Hot magma comes to the surface, seeps out, and is cooled. Land masses also rise as the land is eroded and pushed up from below.

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