VIEWS: 13 PAGES: 7 POSTED ON: 12/15/2011
The Earth's Biosphere (kidgeo.com) The biosphere is the defined as the sphere or area around the planet Earth where life exists. This zone of life is vast. Most life forms live on, or near the surface of Earth. However, some live deep within the hydrosphere (oceans, lakes, and streams), while others thrive in the depths of the lithosphere (solid portion of Earth). For this reason, mapping the exact borders of the biosphere is quite challenging. Life Affects The Landscape The life forms that make up the biosphere do more than just live on Earth. They also interact with it, and are responsible for making great changes in the way that the Earth has evolved. Without life the planet Earth would have evolved very differently. Consider the atmosphere. Our atmosphere is comprised of approximately 21% oxygen. Where did that oxygen come from? The early Earth did not have very much oxygen in the air. Most of it had been trapped by the seas, and locked up in the rocks and soil. Slowly over millions of years, plants released oxygen into the air, greatly increasing its abundance, and making animal life possible. Life affects the landscape in many other ways. Plant roots help keep soil from being carried away by rain water. Small rodents and reptiles dig tunnels, beavers build damns, creating temporary lakes, and ponds, and humans build a variety of projects large and small. Geographer Versus Biologist Biology is the study of life. Biologists are scientists who study life forms in all their varieties, and who do their best to use their knowledge about these life forms to both protect life on Earth, as well as help mankind. Biologists study the complex systems with each life form. For example, consider a beetle. A biologist is looking to understand how the beetle’s body works. What makes its legs move back and forth, how does it digest its food, how does it fly, and so forth. A geographer is not concerned so much with how the beetle’s body works, but rather, with how the beetle affects the landscape of Earth, as well as how the beetle, and all of its fellow beetles are distributed around the Earth, and so forth. Biologists study the life form itself, and how it works, while geographers look at how the same life form affects the Earth, other life forms, and how they are distributed throughout the biosphere. Cycles, Balance, And Life For hundreds of millions of years the chemicals and elements found on Earth have remained relatively constant, or in other words, they have changed very little. The amount of one element or chemical in the Earth’s surface is practically the same as it was many millions of years ago. This consistency is one of the things that makes life on Earth possible. This balance is maintained via complex interactions or cycles between the Earth, and its organisms, or life forms. The elements of the Earth are taken into life forms, used to sustain the organism, and later released in the form of waste, or through decomposition upon the death of the organism. Most of these cycles only take a few months, or a few years to complete. However, some can take many millions of years. The Energy Cycle Each day as the Sun rises, the world is showered with heat and light. This energy from the Sun is very important to all life on Earth. Without it, life could not exist. While most of the heat and light that reaches the Earth is either reflected, or radiated back into space, some of it is captured by plant life through the process of photosynthesis. Photosynthesis takes place when plants use sunlight in order to produce sugars. These sugars can than be used by the plant as food, in order to sustain the functions of life. Animals do not have the ability to produce our own food. Thus we must obtain our energy by eating plants, or by eating other animals that have eaten plants. At some point as plants, or animals die, or release waste into the environment, the heat from the Sun is released back into the environment. The Hydrologic Cycle The process of water moving through the environment is referred to as the hydrologic cycle. Water is found throughout the biosphere, and is probably the most important substance needed to sustain life forms. Humans can survive for many weeks without the energy obtained by eating food, however, we would only last a few days without water. Water is used to carry out the many important, and complex chemical reactions that all life forms must perform in order to survive. Water carries nutrients to various parts of a life form, and carries waste away from the different parts of a life form. Because water is so important, the most abundant substance in any organism is water. The water found within your body as you read this article has been used, and re-used by organisms throughout the history of Earth. It is quite possible that there is water found in your body that was once inside of a Tyrannosaurus Rex. The Carbon Cycle Carbon is an important element to living things. As we learned earlier, the most abundant substance in organisms is water. The second most abundant substance is carbon. Much of the solid portions of life forms is made up of great amounts of carbon. How do living things obtain carbon? Carbon is extracted from the atmosphere by plants through the process known as photosynthesis. This carbon is combined with other elements in complex ways to form organic molecules important to life. This carbon is later transferred to animals who consume or eat plants. When plants and animals die, much of their carbon is returned to the atmosphere as the organisms decompose. Every so often, a plant or animal does not decompose right away. Their bodies are trapped, in locations where decomposition can simply not take place. This is most common at the bottom of oceans and seas, where the life forms become buried by sand. Instead of returning to the atmosphere, the carbon from these life forms is trapped within the Earth. Over millions of years more and more of the carbon on Earth has been trapped in this manner. Today, almost 99% of all the carbon on Earth has been locked up deep within the Earth. As rocks weather, this carbon is slowly released back into the atmosphere, creating a balance. For the past several hundred million years, the amount of carbon being locked up in the Earth, and the amount being released by weathering rocks was almost perfectly balanced. This important balance has been altered significantly in the past century, as humans have begun using fossil fuels to produce energy. By burning the Earth’s store of carbon, mankind is able to create the energy needed to operate our communities. However, we must be careful as we do so. By releasing more carbon into the atmosphere than is being locked up, we risk causing damage to the delicate carbon cycle. The Oxygen Cycle Oxygen exists in our modern atmosphere in great amounts. Approximately 21% of the atmosphere is comprised of oxygen. This was not always the case however. Billions of years ago, it is believed that there was virtually no oxygen found in the atmosphere at all. What caused an increase in oxygen levels? Most of the oxygen now found in our atmosphere was released by plants, as a bi-product of photosynthesis. Over millions of years, as plants around the globe released oxygen, the levels continued to rise, until they reached a balance around 1 billion years ago. For the last billion years, the amount of oxygen has remained relatively constant. At the same time that plants continue adding oxygen to the atmosphere, it is also being removed by various processes. Oxygen is highly reactive. As the oxygen in our atmosphere interacts with other substances, it often bonds to them, becoming trapped. Many life forms also remove oxygen from the atmosphere, as they breath. This oxygen is used by these life forms to carry out the functions of life. The Nitrogen Cycle Nitrogen is the most abundant element in our planet’s atmosphere. Approximately 78% of the atmosphere is comprised of this important element. Nitrogen is used by life forms to carry out many of the functions of life. This element is especially important to plant life. Yet nitrogen in its gaseous form is almost entirely unusable to life forms. It must first be converted or ‘fixed’ into a more usable form. The process of converting nitrogen is called fixation. There are specialized bacteria whose function it is to fix nitrogen, converting it, so that it can be used by plants. There are still other bacteria who do the reverse. That is, they return nitrogen to its gaseous form. After nitrogen is fixed, it can be absorbed, and used by plants, and subsequently by animals. The process of nitrogen being fixed, used by plants and animals, and later returned to the atmosphere is referred to as the nitrogen cycle. Food Chains and Webs In previous sections we have studied how the many different substances needed for life are passed from the Earth to life forms, and than from one life form on to another, until these substances are eventually returned to the Earth. These many different cycles are primarily carried out as one organism consumes, or eats another in a complex chain known as the food chain. The most important part of any food chain are the plants that take the energy from the Sun, and substances from the atmosphere and soil to produce food. As one organism eats another, it uses a portion of these substances to sustain itself, and discards the rest in the form of waste. "Basic" Food Chain Classifying Life Forms On the Earth today there are approximately 600,000 different types of plants, and over one million different kinds of animals. Remember that one of the goals of geographers is to understand how life forms are distributed throughout the Earth. With nearly 2 million different types of life forms on Earth, the task of mapping out, and understanding their distribution can be over whelming. In order to aid them in their goals, geographers group life forms into categories based on how they are the same, and how they are different. For the purpose of geography, the two main groups are flora, and fauna. Flora consists of all the plant life on Earth, while fauna refers to animal life. Within the oceans, geographers sometimes categorize life forms a little differently. Instead of two major groups, they consider three. These are plankton, nekton, and benthos. Plankton consist of any plants and animals that float in the water. Nekton are the animals, such as fish, squid, and sharks that can swim about freely from place to place. Benthos are the plants and animals found on the ocean floor. Ecosystems The plants and animals that are found in a particular location are referred to as an ecosystem. These plants and animals depend on each other to survive. In a delicate balance, these life forms help to sustain one another in regular patterns. Disruptions to an ecosystem can be disastrous to all organisms within the ecosystem. As an example, consider what happens when a new plant or animal is introduced into an ecosystem, where it did not before exist. The new organism competes with the natural organisms from that location for available resources. These unnatural strangers can push other organisms out, causing them to become extinct. This can then affect still other organisms that depended on the extinct organism as a source of food. Throughout the history of the Earth, the delicate balance found within ecosystems have been disrupted by natural disasters such as fires, floods, storms, volcano eruptions, and so forth. In recent years however, mankind has increasingly been affecting the many ecosystems around the world. Biomes As geographers study the many ecosystems around the world, many similarities or patterns become evident from one ecosystem to another. This allows scientists to group ecosystems into categories called biomes. The most commonly accepted biomes that exist on the Earth are Tundra, Desert, Grassland, Tropical Rain Forest, Deciduous Forest, and Coniferous Forest. Though there is some debate among scientists as to exactly how biomes should be classified.
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