When you study the structure of the Earth's surface or Earth's atmosphere, did you know that you are studying the subject of geography? Geography is the broader category which includes both of these subcategories. Learning about the Earth by exploring its surface, the various oceans, the atmosphere and also how animals, people and plants are distributed is geography. It is a science that encompasses the distribution, description and interaction of different biological, cultural and physical aspects of the surface of earth.
How do scientists know what is at the center of the Earth when no one has actually ever seen it? Scientists use seismic waves to sense the Earth's core. Think of the waves that are produced by an earthquake or by a man-made explosion. These waves are considered seismic waves. Seismic waves can be measured as they pass through Earth, and they react differently when encountering different materials. The Earth has a magnetic field that scientists also use to learn about the planet core. Large circulations of hot liquid mantel under the Earth's surface create the magnetic field. The majority of Earth is covered by oceans (approximately 70 percent). The continents comprise the other 30 percent of the surface. Basalt and granite are also a large part of Earth's surface. Scientists have divided Earth into four layers including: the crust, mantle, outer core and inner core. The initial and thinnest layer of Earth is called the crust. It is comprised of rock and other loose materials. Silicon, calcium, potassium, aluminum and sodium help to create this layer which is about three times thicker underneath the continents than it is under the oceans. The next layer is referred to as the mantle. The mantle is directly below the crust. It has layers which are comprised of hard, rigid rock followed by a layer of super-heated solid rock and ending with a layer of solid and sturdy rock. In the mantle you will find oxygen, iron, magnesium, calcium, silicon and aluminum. The outer core is the next layer of Earth which consists of super-heated liquid molten lava. The lava is mostly iron and nickel. Scientists believe the outer core controls Earth's magnetic field. Earth's final layer is the inner core which is also mostly nickel and iron. This layer is a solid mass.
What is Earth's atmosphere? Basically it is air. Without air, life on Earth would not be possible. A variety of gases and particles comprise air. There are three primary gases which include nitrogen, argon and oxygen. Many other gases also exist in tiny amounts. Small particles can be found floating in the atmosphere such as dust and pollen. Air itself cannot be seen, smelled nor tasted while particles can often be seen such as smoke. Earth's atmosphere extends from its surface to approximately 6,000 miles above Earth. Scientists have divided the atmosphere into various layers beginning at Earth's surface and including: the troposphere, stratosphere, mesosphere, thermosphere and exosphere. The mesosphere and thermosphere are often referred to as the ionosphere because of the manner in which they reflect the Sun's ionized energy. There are differing amounts of pressure in the various layers of the atmosphere which greatly effect weather, people, animals and man-made devices. Basically the higher you travel from the surface of the Earth, the less compressed the atmosphere becomes, and the less pressure is exerted on items existing in that atmosphere. When you climb a mountain, you are actually traveling higher into the atmosphere as the air becomes cooler. There are several gases in the atmosphere which have a huge effect on weather throughout the world. Carbon dioxide is able to absorb infrared radiation (heat) that the Sun sends to Earth. Due to this aspect of carbon dioxide, the lowest layer of the atmosphere is warm enough to sustain life. It keeps Earth insulated. Carbon dioxide is naturally found in the air, but humans also add small amounts to the air when we breathe out. The burning of fossil fuels adds even more carbon dioxide to the air which may help to cause the temperature of Earth to rise. Another important gas in the atmosphere is ozone which is mainly found in the ozone layer. This gas is able to absorb ultraviolet radiation from the Sun which is vital to life on Earth. It protects animals and plants from getting too much of the Sun's dangerous UV rays. Water vapor is another important gas in the atmosphere. On average the amount of water vapor in the air remains constant but varies a large amount from one area to another. Water vapor causes much of what humans consider to be weather. Water vapor also has a huge impact on temperature.
Earth's hydrosphere encompasses all of the water on, under and over the surface of Earth. The hydrosphere is one of four overlapping spheres that scientists have divided Earth into. The other three spheres include: the atmosphere, biosphere and lithosphere. The hydrosphere affects the evolution of life, erosion and weather. Some of the water supply is temporarily part of many life forms. Most life forms are comprised of at least 50 percent water. The hydrologic cycle refers to the main process involved with moving water around Earth. Through evaporation, water from lakes, streams and oceans is brought into the atmosphere and returned to Earth's surface through rain. Oceans also absorb large amounts of solar energy which the currents transport from the equator toward the Poles. There are four distinct oceans that comprise most of the water on Earth including: the Pacific, Atlantic, Indian and Arctic. There are also designated gulfs, bays and seas which are generally smaller parts of one of the larger oceans. The largest ocean is the Pacific which covers more space than the combination of all of the continents combined. Surface water is located on continent and island surfaces and comprises 25 percent of Earth's total water. Lakes are responsible for 90 percent of surface water.
Our living world is considered the biosphere. It includes animals, plants, bugs, fungi and even two single-celled living things (prokaryotes and eukaryotes). It extends to upper areas in the atmosphere where birds and insects can be found. It also includes areas deep in the ground or at the bottom of the ocean where life of some type exists. Any place on Earth where life exists is part of the biosphere. All the spheres work together in the biosphere to create our living world such as land interacting with air. Living things depend on each other and the environment for survival. Life forms interacting with Earth have made significant changes in the way Earth has evolved. For example, plants have slowly over millions of years released oxygen into the air which has made life on Earth possible. The landscape is affected by life as well. Plant roots help to protect soil from being washed away by rain water. Beavers build dams that create lakes and ponds that are temporary. Also, humans build many projects that affect the landscape.
Natural cycles (such as the previously mentioned water cycle) exist on Earth to help regulate and balance our planet and its atmosphere. Things that humans do can cause serious changes in the natural cycles which can cause changes in climate. One of Earth's cycles is known as the carbon cycle. Everything that is living is made of carbon including rocks, air and the oceans. Carbon dioxide is a gas formed by carbon attaching to oxygen. Plants need sunlight and carbon dioxide to make food and to grow. Carbon becomes part of plants. Dead and buried plants may become fossil fuel consisting of carbon such as oil and coal for millions of years. Carbon is considered a greenhouse gas and it traps heat in the atmosphere which warms Earth. Due to the burning of fossil fuels by humans there is 30 percent more carbon dioxide in the air today than 150 years ago which has made Earth warmer.
Another of Earth's cycles is the rock cycle. Throughout thousands of years, the Sun's energy caused wind and water on Earth's surface to move. The force of the movement was strong enough to break rocks into types of sediment such as sand. When sediment becomes buried and solidifies it creates sedimentary rock like shale or sandstone. When rocks are deeply buried, the environment becomes high pressure and very hot. This causes the texture of rocks and crystals to change into metamorphic rocks such as slate or marble. Very deep underground rocks actually melt from extreme pressure and temperature and form molten rock (magma). Magma can cool deep underground and form igneous rock. It can also flow to the Earth's surface through a volcanic eruption. Rocks can actually affect Earth's atmosphere. Tiny ash particles and gases can be sent into the air when volcanoes erupt. The particles of ash can help to make raindrops when water condenses around them. When gases are released from a volcano they can become sulfuric acid droplets which can block out sunlight. If the volcanic eruption is big it can affect the temperature of Earth for months or even years.
Since the water cycle was previously explained, the nitrogen cycle is the final cycle. Eighty percent of air is nitrogen. Every living thing needs nitrogen. Humans get the necessary nitrogen in order to grow from food. Soil is where the majority of plants get their nitrogen. Many farmers use fertilizers on their soil that adds nitrogen. Forest fires and fertilizers add huge amounts of nitrogen to soil as well as nearby rivers and lakes. When water has too much nitrogen in it, the plants and algae grow rapidly and die all at once when the environment cannot support so many.
There are many online games that are available to teach you about geography. You can have lots of fun while learning at the same time. The following links all provide fun games for kids regarding geography.