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Energy does not cycle the way nutrients and atoms do. Energy enters the ecosystem from the Sun and exits after the organisms have taken as much as they need. Organisms release energy back into the biosphere as heat. Energy also enters the ecosystem from the interior of the Earth. It is usually in the form of heat, not the electromagnetic radiation from the Sun. There are finite amounts of carbon (C), nitrogen (N), and oxygen (O) on the planet. Those elements are recycled through the planet’s resources. Energy is different in that it comes into the biosphere and then leaves.
Starting With The Sun
Our major source of energy is the Sun. Millions of miles away from Earth; our star has millions of nuclear reactions creating a large amount of energy. A small amount of that energy makes it to Earth. There are many different types of energy. We get visible light, heat, and ultraviolet radiation. Not all of it is good for the planet, but it all changes our world. The Earth absorbs only a small percent of the total energy hitting the planet.
The living organisms of the Earth generally use the heat (infrared radiation) and the visible light. The heat is good for everyone and lets our planet maintain a temperature where life can survive. The most important use of the visible light is to (1) see and (2) help plants run the process of photosynthesis. Photosynthesis is a process that happens when the energy from the Sun is used to power a chemical process that creates sugars and starches.
When Input Is Not Equal To Output
The amount of energy getting to the Earth is equal to the amount of energy leaving plus the amount used. Sometimes energy is trapped by the planet. There is a situation called a greenhouse effect that causes the energy of a planet to slowly increase over time. In the modern world we produce many compounds that float around in the atmosphere. If enough of these compounds were present, the infrared radiation reflected by the Earth could become trapped in the atmosphere and the temperature would slowly increase.
The Carbon Cycle
Carbon (C) is the basis of life on Earth. Scientists consider 99.9% of all organisms on the planet to be carbon based life. Those organisms need carbon to survive. Whether the carbon is in the form of a sugar or carbon dioxide gas, we all need it. Unlike energy, carbon is continuously cycled and reused. The Earth only has a fixed amount of carbon. The carbon cycle is the ultimate form of recycling.
Start With Plants
Plants are a good starting point when looking at the carbon cycle on Earth. Plants have a process called photosynthesis that enables them to take carbon dioxide out of the atmosphere and combine it with water. Using the energy of the Sun, plants make sugars and oxygen molecules. All of the non-photosynthetic creatures on the planet use the oxygen. Every creature on the planet uses the sugars and starches created by plants.
Then Animals Eat The Plants
Animals are the non-photosynthetic creatures of the planet. They are not able to create their own food. Instead, they eat plants or other animals. The sugars and starches they eat are broken down by a process of metabolism. The results are energy for the creature, water, and carbon dioxide molecules. The carbon dioxide then returns to the atmosphere where the plants use it again.
Who Eats The Animals?
There are also decomposers involved in the carbon cycle. They break down organic material such as dead animals, poop, or leaves. Decomposers are able to break down the chemical compounds inside the body. They also release carbon dioxide as well as methane.
Sometimes the decomposers don’t break down organic material. There are great oil fields under the surface that are made of plants that did not decompose millions of years ago. There are also layers of rock made of millions of creatures who had shells. One day this carbon will return to the everyday carbon cycle, but geological processes are much slower than living processes.
Cycling Water
Water water everywhere and always moving around. Even the smallest water molecule at the bottom of the ocean is moving. It just moves really slowly. We’re going to talk about the hydrologic cycle. This is the path water takes when it moves through the oceans, through the sky and through life on land. It’s a never ending cycle that keeps life on Earth alive.
Just Flowing Through
Water cycles and flows through ecosystems. Water is recycled on a global scale. It’s actually a cycle through the biosphere, not just through local ecosystems. It may flow from one ecosystem to another on its way from the air to the land and back to the oceans. Also, a great amount of fresh water below the surface of the Earth that is cycled over long periods of time.
The Overview
Even though there is no real starting place, we’ll start the cycle in the atmosphere. Water in the atmosphere is found in clouds and water vapor. Slowly the entire atmosphere circulates around the planet. When weather is created one of the most common results is precipitation. Precipitation is the process of water condensing in the atmosphere. It could be rain, snow, drizzle, fog, dew, or hail. Whatever path, the water comes out of the atmosphere and makes it to the surface. Scientists also use the term hydrological cycle to when discussing water’s movement through the biosphere.
Once on the surface, water is still moving around. Snow can melt and become rivers that flow into the oceans. Water can collect underground (groundwater). Water can collect in the oceans. Over 60% of the surface of the planet is covered by water. Beyond collecting, water can return to the atmosphere. Water moves from the ground or oceans into the atmosphere through a process called evaporation. It’s a process that happens on a molecular level when the molecules of water are really energized and rise into the air.
Now you’ve got water in the air and water on land. Organisms all over the Earth need water to survive. Although it’s a small amount when compared to oceans, every living creature is filled with water. Our cells are mainly composed of water. The human body is 80% water. Eventually, when an organism dies, the water is returned to the system, but you should know that living things borrow water on a regular basis.
Life Of A Water Molecule
So you’re a water molecule. Chances are you’ll stay a water molecule and won’t ever be broken down. The world likes to keep its water around. You’re moving through the hydrologic cycle. You evaporate, fall in rain, and drain in a river. Not a lot of excitement. But how much time does it take? Scientists think that if you are lucky enough to be evaporated into a cloud that you spend about ten days floating around the atmosphere. If you’re unlucky enough to be at the bottom of the ocean, or stuck in a glacier, you might spend tens of thousands of years without moving.
Oxygen Cycling
Oxygen (O) atoms cycle through the ecosystem and the biosphere the way other elements do (especially carbon). The Earth has a fixed supply of the element even though it can be found everywhere, including the atmosphere, the oceans, rocks, and all living organisms. While not all organisms need to breathe oxygen, there is definitely oxygen inside of every organism.
Oxygen Rarely Alone
Oxygen is one of the major compounds found in the atmosphere of the Earth. You never find oxygen floating around as individual atoms. Oxygen is always with other elements. You may find an oxygen molecule that has two oxygen atoms. There are molecules with three oxygen atoms called ozone. You will also find oxygen bound in water molecules and carbon dioxide. That oxygen floats through the atmosphere until it comes down to Earth and starts one of many cycles.
Dissolved In Water
There is a large amount of oxygen dissolved in the water of oceans, lakes, and streams. As water moves, the oxygen is forced into solution. The organisms that live in the water breathe that oxygen by filtering it out of solution the way we do with the air. Over millions of years oxygen has also become an integral element in our rocks and land. Oxygen bonds with silicon (silicates), iron, and carbon (carbonates) to form many of the compounds in rock. Creatures like lichen are able to break down the rocks over thousands of years and release nutrients into the soil. We Need Oxygen To Survive
Last are the organisms of the world. They use oxygen in many forms. Their role in the cycle begins with carbon dioxide in the atmosphere. Plants take in that carbon dioxide and combine it with water to create sugars and oxygen molecules. Animals breathe that oxygen and both plants and animals use the sugars for energy. Through the process of metabolism, the sugars are broken down into water and carbon dioxide. Then the cycle begins again.
The Nitrogen Cycle
Nitrogen (N) is an element like carbon. All creatures need nitrogen to survive. There are huge amounts of nitrogen gas in the atmosphere, but most animals and plants have no way of using it. It needs to be fixed (put into a biologically useful compound). After it is fixed, it can then start to move through the cycles and organisms in an ecosystem.
Where Can You Find It?
Let’s start with the main sources of nitrogen. Nitrogen gas is the most abundant element in our atmosphere. The other main source of nitrogen is in the nitrates of soil. The nitrogen in the atmosphere cannot be used while the nitrates in the soil can be used by plants. Nitrogen can be converted into useful nitrate compounds by bacteria, algae, and even lightning. Once in the soil, the nitrogen becomes biologically accessible.
Borrowing Nitrogen
Plants are the main users of nitrogen in the soil. They are able to take in the nitrates through their root system. Once inside the plant, the nitrates are used in organic compound that let the plant survive. Organic compounds have carbon atoms. Those compounds might be proteins, enzymes, or nucleic acids.
Once the plants have converted the nitrogen, the element can be returned to the soil or taken up by animals. Herbivores eat plants and convert many of the amino acids into new proteins. Omnivores that eat both plants and animals are able to take in the nitrogen rich compounds as well. The nitrogen compounds are only borrowed. Nitrogen atoms are returned to the soil in poop and dead organisms. Once in the soil, the whole process can start again.
Yes. Iron Cycles Too.
Iron (Fe) atoms also cycle through the ecosystems of the world. Although there is cross-over, there is a difference between the cycling on land and in the water. The differences are based on how the producers get their iron in the first place. Iron must be in the seawater for sea plants and phytoplankton to use it. A great deal of iron is in the soil or other organisms for the land creatures to consume.
Start With The Plants
As with many cycles, the iron cycle starts with plants. Plants on land get their iron from the soil. Iron is an abundant element on the planet so you will find it in many rocks and biomes. Good soils are often rich in iron compounds. Iron also gets into the soil when organisms die and sometimes when they poop. All organisms use iron in some form. Iron is an essential nutrient. Many enzymes require iron to work. So plants get iron out of the soil and into their tissues.
Then The Animals
Animals need plants to get iron into their systems. You might get iron by eating beets, carrots, celery, or potatoes. If you eat meat you will get a lot of iron from eating the flesh of other animals. The main point is that animals need to eat substances that have already absorbed iron. We can’t get our iron from the soil or by eating rocks. Humans use iron in their hemoglobin. Hemoglobin is the compound that carries oxygen through the body. A lack of iron in the diet results in a disease called anemia.
Iron Does An Organism Good
Once the iron is captured from the environment it is free to circulate between plants and animals. Scientists have even tried to stimulate the growth of plants in the ocean by adding iron to the water. The phytoplankton grew more with the extra iron, but it was only a temporary effect. Iron usually makes its way into the ocean from runoff or from the dust circling the earth. When a volcano erupts, large amounts of dust are sent into the atmosphere. That iron rich dust lands on the soil and in the ocean.
Cycling Phosphorus
Phosphorus (P) is another one of the essential elements that cycle through the ecosystem. It is an element that is found in the ground and then taken up by plants and animals. Phosphorus starts its existence as phosphate ions (PO4) in the rocks of the world. When it rains, the phosphates and other minerals are removed from the rocks and distributed in soils and the water all over the planet.
Plants Need It
Plants on land take in the inorganic (compounds without carbon) phosphorus compounds from the soil. The phosphorus atoms are then incorporated into many organic compounds that are used in cells. Animals can get their phosphorus by eating plants or drinking water. Algae and water plants are able to absorb the ions from the water. Unlike carbon and nitrogen, the phosphorus cycle is not a true cycle. There is a great deal of phosphorus lost.
Losing The Element
Phosphorus has a tendency to wind up at the bottom of the ocean. Once at the bottom, the phosphate ions are lost to the world. Sometimes the phosphates are found in runoff water and go to the bottom and sometimes human poop contains phosphate and those phosphates are returned to the ocean. The problem is that all usable phosphorus sources are on the surface The atoms are useless once they reach the bottom of the ocean. Slowly but surely the surface of the Earth is running out of easy places to find phosphorus.
Elemental Concern
Why is there a sudden concern? Phosphorus only gets into the soil by the weathering process on rocks. When plants die in the natural world, the phosphates return to the soil. In farming, the crops are taken away and then over many years the soil runs out of phosphorus compounds. We have created a situation where we must artificially replenish the nutrients in the land. Phosphorus is heavily used in the farming industry and fertilizers filled with phosphates are used all over the world to help plants grow
Start At The Center
With the exception of a few meteorites, all of the rocks on the surface of the Earth started beneath the surface. Combinations of magma flowing beneath the crust, upheaval, and plate tectonics keep the rocks of the world circulating in the same way that water and air circulate. One big difference is that rocks cycle very very very slowly. A million years is a short period of time for rocks.
As a hot Earth cooled millions of years ago, the crust began to form. Those were the first rocks. With the movement of the surface, newer rocks have appeared over time. For our example we’re going to follow the rocks near a volcano. Simply enough… The molten rock oozed out of the volcano and wound up near the surface.
Forced Up
As that magma moved towards the surface, our example is going to see a pool form just beneath the surface in a pluton. As this pool of igneous rock cools, it was close, but didn’t break the surface. Since our example volcano was near a fault line, there was a lot of tectonic activity beneath the surface. That activity and movement applied pressure on the pluton and the rock was changed from an igneous form to metamorphic. Given a few million more years, tectonic activity forced that metamorphic rock to the surface and eventually to the top of a mountain.
Falling Down
When you’re at the top of a hill or a mountain there is only one direction you can go. Down. Let’s bring in a little erosion and weathering that will break up the metamorphic rock. It starts simply enough by breaking the mountain into boulders and then smaller rocks. A few landslides help the process move a bit faster too. Remember we’re working with thousands and millions of years. Those rocks slowly move downhill and are small enough to be carried away in the runoff water. The runoff carries the small pieces of stone in the form of sand to an area where the sediment collects.
These super small rock fragments can go in a few directions from here. There may not be any vegetation and the sediment continues to build up over time. Eventually, sedimentary rock types may be created. Some examples might be some nice limestone or sandstone near the coasts. The other direction would be to break down even more into the basic elements of the rock. The plants in the region can then use those elements as their roots reach out for nutrients.
From A Mountain To Atoms
Now we’re thinking on a microscopic level. Rocks have been broken down into sand and the sand into fine powder. These smaller particles are more easily subject to biological break down by basic organisms such as lichen, molds, or algae. They take a few atoms of nutrients at a time. Looking at one day it’s not that impressive. But if you think of millions of microscopic organisms working over thousands of years, its starts to make a dent. Once those nutrients are available to organisms, the elements take a new road.
The chemistry of the world can also break down these small pieces of rock. Oxidation reactions are only one example of the way the chemical makeup of the rocks can be changed. The thing to remember is that rocks don’t always wind up as little rocks. There is a final phase of their existence when they become a part of many biological cycles
Moving and Flowing
As you have learned about the biosphere, biomes, and specific ecosystems, we have been mentioning the cycles all around you. Whether you look at the food chain or the growth and reduction of populations, ecosystems are always shifting and changing. Forests have spring when plants bloom, autumn when they lose leaves, and winters in the snow. The cycle begins again the next spring.
There are also cycles for the components and the pieces that keep everything alive. There are cycling and flowing nutrients, molecules, and energy. For example, we have mentioned the water cycle several times. Water evaporates, condenses in clouds, falls as rain, and often returns to the oceans. Biogeochemical cycles cover all of the cycles on Earth that relate to biological, geological, and chemical factors.
Bio-Geo-Chemical
Wow. Talk about a word that describes everything on Earth. The world’s cycles all fall under the big grouping of biogeochemical cycles. Let’s break it down.
BIO: Biology. Life. Living things. The biological elements of these cycles play a role in the lives of organisms. The cycles might limit the organisms of Earth or they might happen alongside, changing the environment. For example, when oxygen (O) is found in you or in a plant, it is in the biological phase of its cycle. When a substance is in this portion of a cycle, it is in a biotic phase.
GEO: Earth. Rocks. Land. Air. The ‘geo’ portions of the cycles refer to the non-living or abiotic phases. For example, oxygen cycles through many systems. When oxygen winds up in rocks as iron oxide (FeO) or a crystal, it is in the ‘geo’ part of its cycle.
CHEMICAL: Molecules. Reactions. Atoms. These are the chemical factors involved in the cycles. Complete molecules are not always passed from one point to the next. Chemical reactions change the molecules by building and breaking chemical bonds. These chemical interactions may be small, but they are very important.
Oxygen, for example, is included in all oxidation reactions. One minute oxygen might be in the air and then it is involved in rusting an iron pipe. Carbon (C) offers another important example of chemical factors involved in a cycle. Carbon dioxide (CO2) is found in the atmosphere. It is ‘fixed’ into sugar molecules when plants go through photosynthesis. It moves from an inorganic form to an organic and biologically useful form.
Most of the cycles we discuss will involve the recycling of molecules and nutrients that can be used in systems over and over again. You need to remember that all cycles involve biological, geological, and chemical elements.
