Category The World Around us

The earth is continually recycling the essential ingredients for life — carbon, oxygen, nitrogen and water. All plants and animals play their part in this recycling process.

Energy flows directionally through ecosystems, entering as sunlight (or inorganic molecules for chemoautotrophs) and leaving as heat during the many transfers between trophic levels. However, the matter that makes up living organisms is conserved and recycled. The six most common elements associated with organic molecules (carbon, nitrogen, hydrogen, oxygen, phosphorus, and sulfur) take a variety of chemical forms and may exist for long periods in the atmosphere, on land, in water, or beneath the earth’s surface. Geologic processes, such as weathering, erosion, water drainage, and the movement of the continental plates, all play a role in this recycling of materials. Because geology and chemistry have major roles in the study of this process, the recycling of inorganic matter between living organisms and their environment is called a biogeochemical cycle.

The components of organic molecules are constantly being stored and recycled as part of their biogeochemical cycle. Water, which contains hydrogen and oxygen, is essential to all living processes. The hydrosphere is the area of the earth where water movement and storage occurs. Water can be liquid on the surface and beneath the surface or frozen (rivers, lakes, oceans, groundwater, polar ice caps, and glaciers) or exist as water vapor in the atmosphere. Carbon, found in all organic macromolecules, is an important constituent of fossil fuels. Nitrogen, a major component of our nucleic acids and proteins, is critical to human agriculture. Phosphorus, a major component of nucleic acid (along with nitrogen), is one of the main ingredients in artificial fertilizers used in agriculture and their associated environmental impacts on our surface water. Sulfur, critical to the 3–D folding of proteins (as in disulfide binding), is released into the atmosphere by the burning of fossil fuels, such as coal.

The cycling of all of these elements is interconnected. For example, the movement of water is critical for the leaching of nitrogen and phosphate into rivers, lakes, and oceans. Furthermore, the ocean itself is a major reservoir for carbon. Thus, mineral nutrients are cycled, either rapidly or slowly, through the entire biosphere, from one living organism to another, and between the biotic and abiotic world.

Water is the basis of all living processes. More than half of the human body is made up of water, while human cells are more than 70 percent water. Thus, most land animals need a supply of fresh water to survive. However, when examining the stores of water on earth, 97.5 percent of it is non-potable salt water. Of the remaining water, 99 percent is locked underground as water or as ice. Thus, less than 1 percent of fresh water is easily accessible from lakes and rivers. Many living things, such as plants, animals, and fungi, are dependent on the small amount of fresh surface water supply, a lack of which can have massive effects on ecosystem dynamics. Humans, of course, have developed technologies to increase water availability, such as digging wells to harvest groundwater, storing rainwater, and using desalination to obtain drinkable water from the ocean. Although this pursuit of drinkable water has been ongoing throughout human history, the supply of fresh water is still a major issue in modern times.

The water cycle is driven by the sun’s energy as it warms the oceans and other surface waters. This leads to the evaporation (water to water vapor) of liquid surface water and the sublimation (ice to water vapor) of frozen water, which deposits large amounts of water vapor into the atmosphere. Over time, this water vapor condenses into clouds as liquid or frozen droplets, which is eventually followed by precipitation (rain or snow), returning water to the earth’s surface. Rain eventually percolates into the ground, where it may evaporate again (if it is near the surface), flow beneath the surface, or be stored for long periods. More easily observed is surface runoff: the flow of fresh water either from rain or melting ice. Runoff can then make its way through streams and lakes to the oceans or flow directly to the oceans themselves. Rain and surface runoff are major ways in which minerals, including carbon, nitrogen, phosphorus, and sulfur, are cycled from land to water.

Carbon, the second most abundant element in living organisms, is present in all organic molecules. Its role in the structure of macromolecules is of primary importance to living organisms. Carbon compounds contain especially- high forms of energy, which humans use as fuel. Since the 1800s (the beginning of the Industrial Revolution), the number of countries using massive amounts of fossil fuels increased, which raised the levels of carbon dioxide in the atmosphere. This increase in carbon dioxide has been associated with climate change and other disturbances of the earth’s ecosystems. It is a major environmental concern worldwide.

The carbon cycle is most easily studied as two interconnected sub-cycles: one dealing with rapid carbon exchange among living organisms and the other dealing with the long-term cycling of carbon through geologic processes.

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An ecosystem is any area that can support different living things, and as such can be almost any size. A droplet of rain may contain bacteria and other microscopic living things that live off one another, and could therefore be described as an ecosystem.

An ecosystem is a geographic area where plants, animals, and other organisms, as well as weather and landscape, work together to form a bubble of life. Ecosystems contain biotic or living, parts, as well as abiotic factors, or nonliving parts. Biotic factors include plants, animals, and other organisms. Abiotic factors include rocks, temperature, and humidity.

Every factor in an ecosystem depends on every other factor, either directly or indirectly. A change in the temperature of an ecosystem will often affect what plants will grow there, for instance. Animals that depend on plants for food and shelter will have to adapt to the changes, move to another ecosystem, or perish.

Ecosystems can be very large or very small. Tide pools, the ponds left by the ocean as the tide goes out, are complete, tiny ecosystems. Tide pools contain seaweed, a kind of algae, which uses photosynthesis to create food. Herbivores such as abalone eat the seaweed. Carnivores such as sea stars eat other animals in the tide pool, such as clams or mussels. Tide pools depend on the changing level of ocean water. Some organisms, such as seaweed, thrive in an aquatic environment, when the tide is in and the pool is full. Other organisms, such as hermit crabs, cannot live underwater and depend on the shallow pools left by low tides. In this way, the biotic parts of the ecosystem depend on abiotic factors.

The whole surface of Earth is a series of connected ecosystems. Ecosystems are often connected in a larger biome. Biomes are large sections of land, sea, or atmosphere. Forests, ponds, reefs, and tundra are all types of biomes, for example. They’re organized very generally, based on the types of plants and animals that live in them. Within each forest, each pond, each reef, or each section of tundra, you’ll find many different ecosystems.

The biome of the Sahara Desert, for instance, includes a wide variety of ecosystems. The arid climate and hot weather characterize the biome. Within the Sahara are oasis ecosystems, which have date palm trees, freshwater, and animals such as crocodiles. The Sahara also has dune ecosystems, with the changing landscape determined by the wind. Organisms in these ecosystems, such as snakes or scorpions, must be able to survive in sand dunes for long periods of time. The Sahara even includes a marine environment, where the Atlantic Ocean creates cool fogs on the Northwest African coast. Shrubs and animals that feed on small trees, such as goats, live in this Sahara ecosystem.

Even similar-sounding biomes could have completely different ecosystems. The biome of the Sahara Desert, for instance, is very different from the biome of the Gobi Desert in Mongolia and China. The Gobi is a cold desert, with frequent snowfall and freezing temperatures. Unlike the Sahara, the Gobi has ecosystems based not in sand, but kilometers of bare rock. Some grasses are able to grow in the cold, dry climate. As a result, these Gobi ecosystems have grazing animals such as gazelles and even takhi, an endangered species of wild horse.

Even the cold desert ecosystems of the Gobi are distinct from the freezing desert ecosystems of Antarctica. Antarcticas thick ice sheet covers a continent made almost entirely of dry, bare rock. Only a few mosses grow in this desert ecosystem, supporting only a few birds, such as skuas.

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The biosphere is the part of the Earth in which life exists. It covers an area that stretches from the very bottom of the oceans to some way above the surface of the Earth.

The biosphere is made up of the parts of Earth where life exists. The biosphere extends from the deepest root systems of trees, to the dark environment of ocean trenches, to lush rain forests and high mountaintops.

Scientists describe the Earth in terms of spheres. The solid surface layer of the Earth is the lithosphere. The atmosphere is the layer of air that stretches above the lithosphere. The Earth’s water—on the surface, in the ground, and in the air—makes up the hydrosphere.

Since life exists on the ground, in the air, and in the water, the biosphere overlaps all these spheres. Although the biosphere measures about 20 kilometers (12 miles) from top to bottom, almost all life exists between about 500 meters (1,640 feet) below the ocean’s surface to about 6 kilometers (3.75 miles) above sea level.

The biosphere has existed for about 3.5 billion years. The biosphere’s earliest life-forms, called prokaryotes, survived without oxygen. Ancient prokaryotes included single-celled organisms such as bacteria and archaea.

Some prokaryotes developed a unique chemical process. They were able to use sunlight to make simple sugars and oxygen out of water and carbon dioxide, a process called photosynthesis. These photosynthetic organisms were so plentiful that they changed the biosphere. Over a long period of time, the atmosphere developed a mix of oxygen and other gases that could sustain new forms of life.

The addition of oxygen to the biosphere allowed more complex life-forms to evolve. Millions of different plants and other photosynthetic species developed. Animals, which consume plants (and other animals) evolved. Bacteria and other organisms evolved to decompose, or break down, dead animals and plants.

The biosphere benefits from this food web. The remains of dead plants and animals release nutrients into the soil and ocean. These nutrients are re-absorbed by growing plants. This exchange of food and energy makes the biosphere a self-supporting and self-regulating system.

The biosphere is sometimes thought of as one large ecosystem—a complex community of living and nonliving things functioning as a single unit. More often, however, the biosphere is described as having many ecosystems.

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Scientists who study the relationships between different forms of life on Earth are called ecologists. They divide up the bio-sphere into different, related sections, which makes the relationships easier to understand. These sections are the niche, the habitat, and the ecosystem.

Many different kinds of scientists study the biosphere, using many kinds of tools.

Some scientists go into the field to study animals and plants in their native environments. Some scientists study cellular processes in the laboratory with sophisticated equipment. Some do experiments to see how changes in the environment result in changes in the organism.

NASA scientists use remote sensing to observe a section of the earth each orbit, and then combine the data from many orbits to recreate the whole earth at once. Sensors in space observe the earth in many different wavelengths of light. Combinations of these images can be used to determine what is growing in each patch of the earth, and even if it is healthy or not. As sensors get better and more sensitive, the size of the smallest patch that can be observed from space gets smaller and smaller – to within a few meters now. Remote sensing data can be used in estimating biomass, soil moisture, changes in elevation, or even animal population densities.

At a smaller scale, other scientists may investigate the processes involved in cycling water and the elements of life through the biosphere: carbon, nitrogen, sulfur, phosphorous, and other elements. These studies can also provide “ground-truth” – observations on the ground which are used to validate the remotely sensed data. As more and more observational and experimental data become available, other scientists construct models to help us understand the biosphere, how it evolved, and even provides tools that allow for predicting the future response of the biosphere to global change and human activities.

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As far as we know, the Earth is the only planet in our Solar System capable of supporting life. It has all the things necessary to support life as we know it — water, carbon, oxygen, nitrogen and an abundant supply of food. Life on Earth is incredibly diverse, and the systems that support it are very complex.

Although the exact process by which life formed on Earth is not well understood, the origin of life requires the presence of carbon-based molecules, liquid water and an energy source. Because some Near-Earth Objects contain carbon-based molecules and water ice, collisions of these object with Earth have significant agents of biologic as well as geologic change.

For the first billion years of Earth’s existence, the formation of life was prevented by a fusillade of comet and asteroid impacts that rendered the Earth’s surface too hot to allow the existence of sufficient quantities of water and carbon-based molecules. Life on Earth began at the end of this period called the late heavy bombardment, some 3.8 billion years ago. The earliest known fossils on Earth date from 3.5 billion years ago and there is evidence that biological activity took place even earlier – just at the end of the period of late heavy bombardment. So the window when life began was very short. As soon as life could have formed on our planet, it did. But if life formed so quickly on Earth and there was little in the way of water and carbon-based molecules on the Earth’s surface, then how were these building blocks of life delivered to the Earth’s surface so quickly? The answer may involve the collision of comets and asteroids with the Earth, since these objects contain abundant supplies of both water and carbon-based molecules.

Once the early rain of comets and asteroids upon the Earth subsided somewhat, subsequent impacts may well have delivered the water and carbon-based molecules to the Earth’s surface – thus providing the building blocks of life itself. It seems possible that the origin of life on the Earth’s surface could have been first prevented by an enormous flux of impacting comets and asteroids, then a much less intense rain of comets may have deposited the very materials that allowed life to form some 3.5 – 3.8 billion years ago.

Comets have this peculiar duality whereby they first brought the building blocks of life to Earth some 3.8 billion years ago and subsequent commentary collisions may have wiped out many of the developing life forms, allowing only the most adaptable species to evolve further. It now seems likely that a comet or asteroid struck near the Yucatan peninsula in Mexico some 65 million years ago and caused a massive extinction of more than 75% of the Earth’s living organisms, including the dinosaurs. At the time, the mammals were small burrowing creatures that seemed to survive the catastrophic impact without too much difficulty. Because many of their larger competitors were destroyed, these mammals flourished. Since we humans evolved from these primitive mammals, we may owe our current preeminence atop Earth’s food chain to collisions of comets and asteroids with the Earth.

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Some fish are bred in controlled conditions called fish farms. Fish farmers build special pens in lakes, ponds or estuaries. Here, they hatch fish from eggs and keep them until they are big enough to sell. Also known as “aquaculture”, fish-farming is becoming increasingly common. Freshwater fish farms breed salmon, carp and trout. Oysters and other shellfish are popular in coastal fish farms.

Fish farming is a form of aquaculture in which fish are raised in enclosures to be sold as food. It is the fastest growing area of animal food production. Today, about half the fish consumed globally are raised in these artificial environments. Commonly farmed species include salmon, tuna, cod, trout and halibut. These “aquafarms” can take the form of mesh cages submerged in natural bodies of water, or concrete enclosures on land.

According to the United Nations Food and Agriculture Organization, roughly 32% of world fish stocks are overexploited, depleted or recovering and need of being urgently rebuilt. Fish farming is hailed by some as a solution to the overfishing problem. However, these farms are far from benign and can severely damage ecosystems by introducing diseases, pollutants and invasive species. The damage caused by fish farms varies, depending on the type of fish, how it is raised and fed, the size of the production, and where the farm is located.

One significant issue is that—rather than easing the impact on wild populations—the farms often depend on wild fish species lower on the food chain, like anchovies, in order to feed the larger, carnivorous farmed species. It can take up to five pounds of smaller fish to produce one pound of a fish like salmon or sea bass. Overfishing of these smaller “forage” fish has repercussions throughout the ocean ecosystem.

As is the case with industrial animal farms on land, the fish are often housed in unnaturally crowded and cramped conditions with little room to move. Fish may suffer from lesions, fin damage and other debilitating injuries. The overcrowded and stressful conditions promote disease and parasite outbreaks—such as sea lice—that farmers treat with pesticides and antibiotics. The use of antibiotics can create drug-resistant strains of diseases that can harm wildlife populations and even humans that eat the farmed fish.

Escaped fish introduce yet another threat into the environment. Each year, hundreds of thousands of fish escape farms and threaten the genetic diversity and survival of native species. High stocking densities result in a significant amount of pollution from fish excrement and uneaten food, which in turn lead to poor water quality high in ammonia and low in oxygen. Outdoor fish farms can also attract predatory marine animals, such as sea birds and sea lions, who are sometimes poisoned or shot by aqua farmers for eating the fish.

Despite evidence to the contrary, it is still a common misconception that fish do not feel pain. Slaughter methods in the aquaculture industry are appalling. Little to no attention is given to the suffering of the animals and most are fully conscious during slaughter, which can take many minutes. Some species, such as salmon in the United States, are also starved for many days to empty the gut before they are sent to slaughter. Fish are most often not stunned and are killed by bleeding out, being hit on the head repeatedly, suffocating or freezing. In the US, as with many other countries, there are no regulations to ensure the humane treatment of fish.

Years of unregulated and underreported catches of Bluefin tuna in the Mediterranean Sea and Atlantic Ocean are threatening the existence of this severely overfished species. To meet the high and growing demand for sushi in Japan and elsewhere, ranching of Bluefin tuna is becoming a popular industry and is exacerbating the problem. Fisherman use longlines and purse seines to catch the tuna before they reach breeding age and have time to reproduce. They are then kept in sea farms for 3–6 months and fattened with thousands of pounds of smaller wild-caught fish before being killed and exported.

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