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Life Materials: Nutrient Cycling

What are Life-Materials?

Life-materials are the basic particles of Earth, called elements, that all living organisms build their bodies from. They are sometimes called "bio-elements," and sometimes "nutrients." They are matter and not energy.

Six billion years ago, every atom of every rock, every waterfall, every creature and every thing now on Earth was stardust floating in space, in a whirling cloud of dust and gas called a nebula.This nebula eventually became the solar system

Those atoms of ancient stardust are the basic particles that all matter of Earth is made of, including your body and mine.


All living organisms, from bacteria to blue whales, are made primarily of six elements, all in the same proportion:


Most organisms also require small amounts of life-materials such as iron, copper and iodine. Sixteen elements are required by all organisms. Most plants require a total of twenty-three different nutrients to flourish.

With every breath, and with every chew and swallow, we take life-materials into our bodies and use them. We use these essential nutrients in two ways:

  • for energy to power our bodies (food for metabolism),
  • as materials to build and renew our bodies.

We renew or rebuild our bodies over and over, every day. In his book "The Web of Life" Fritjof Capra describes how rapid this renewal process can be:

"Many of these…changes occur much faster than one would imagine. For example:

Our pancreas replaces most of its cells every twenty-four hours.
The cells of our stomach lining are reproduced every three days
Our white blood cells are renewed each ten days.
98 percent of the protein in our brain is turned over every month.

Our skin replaces its cells at the rate of one hundred thousand cells per minute. In fact, most of the dust in our homes consists of dead skin cells.

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How Life Shares Life-Materials

Life has worked out a wonderful way of sharing these limited Life-Materials. Life re-cycles them, so organisms can share them over time. This sharing process is called Nutrient Cycling. These Life-Materials are shared by all lives on Earth, and have been shared over and over for billions of years.

Imagine a gigantic pool of atoms. Living organisms rise from this pool constantly, so many birthings all the time, here protists and bacteria, there fungi, plants and animals. These newborns drink up atoms from the pool so they can grow, but the pool stays the same size. Dying organisms fall back into the pool just as steadily as others are born.

Every plant, every animal alive on earth this minute is made of life-materials that have been used and re-used by life over and over again.

In other words, every atom of your own body, your physical self, has been part of other living bodies many times before. In a way, parts of you have already been everywhere on Earth. Parts of you have been in bacteria, parts in flowers, and parts have been in dinosaurs.

Death is the central feature of Earth's nutrient recycling program.

But our leftovers from metabolism are also part of Earth's recycling program.

We Need Each Others' Leftovers

Living organisms continually release nutrients from their bodies, in the form of wastes, which are really by-products or leftovers from metabolism. Life takes every opportunity to be creative. One organism's wastes become another organism's nutrients.

For example, every animal on Earth releases carbon dioxide as they breathe. To them, it's just a by-product, and useless. But to every plant on Earth, that carbon dioxide is a necessary nutrient for photosynthesis and continuing life. The plants, in turn, release oxygen into the air, which is necessary for animals. Life on Earth is a balanced process of exchanging each other's leftovers for mutual benefit.

Organisms release all their nutrients when they die and are decomposed (disassembled) by fungi and bacteria. After death our bodies are leftovers. We are done with them, and gradually every part of every body decomposes and returns to the Nutrient Cycles.

All these Life-Material Cycles are equally important. They are all crucial to life on Earth. The Cycles together make an intertwined weaving of many circles that began billions of years ago and has never stopped.

The Cycles are all interrelated, and cannot in truth be separated from each other. But toward understanding, we will pretend we can separate them and will briefly explore the cycling of a few key Life-Materials:

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Water Cycle


Water Facts

Your body is over 60 % water.
Your brain is 90% water. We think with beautifully organized puddles inside a hollow of bones.
Water is a molecule made of two atoms of Hydrogen (H) and one atom of Oxygen (O), so we call it H2O.
Life uses the same water over and over again. This recycling of Earth's water has been going on for billions of years.
Sea water is being lost to the interior of Earth as tectonic plates subduct (sink) into the magma under the seafloor crust.
Subduction loss is made up as we receive millions of gallons of water every day from small ice comets that fall into Earth's atmosphere and become available to life.
Some water molecules in your blood right now are water that has been blood countless times before, and has already flowed down all the rivers on Earth. Some water molecules in your blood were locked in glacial ice ten thosand years.
Some water molecules that are now part of you have recently arrived from space.
Heat from the sun changes liquid surface water (oceans, lakes, wetlands, rivers) into the gas water vapor, which rises into the air. This change of phase is called evaporation.
Another huge source of water vapor in the air is plants. Green plants, especially trees, suck water out of the earth with their roots, and pump it up throughout their bodies, ending in the leaves, which release water vapor. This is called transpiration or evapo-transpiration.
  Large trees transpire hundreds of gallons of water a day. If you study water, you begin to see a forest as a vast series of fountains. Life is deeply involved in the water cycle.
Above the ocean and rain forests, water vapor gathers into clouds. Winds move the clouds of vapor (in North America usually from west to east). The clouds release their water in liquid phase (rain) or crystal phase (snow). The water runs off, or soaks into the ground, and eventually some of it flows into the ocean, where the cycle repeats.

Mind-Play: Follow One Water Molecule

Imagine one molecule of water off the coast of Hawaii.

One sunny day the molecule vaporizes and evaporates up into the air. It rises and becomes part of a cloud.

A few days later, it rains down in Mexico. It is absorbed by the soil. Then a plant root sucks our molecule into itself and the plant makes the molecule part of a flower petal.

After a time, the petal wilts and dries, and the molecule vaporizes again and lifts into the sky.

Imagine the journey continuing. That molecule of H2O might sink deep underground and become ground-water, and it might get pumped up into a faucet to become part of your own blood sometime, or it might get locked up inside a stone or locked up in a glacier for a few thousand years. It might even be in a tear on your pillow.

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The Carbon Cycle

The carbon cycle has many paths.

Carbon Facts

Life on Earth is carbon-based.
Carbon is a lively element that readily combines with other elements to make organic compounds.
A lot of your body, and every body, is made of carbon.
Some carbon parts of your body, right now, were parts of living plants only a few months ago.
Plants make carbohydrates (chemical compounds made of carbon, oxygen and hydrogen, such as wheatseeds that become pasta) that animals eat for food.
You eat the plants, salad or bread or pasta ( or another animal (cow), ate the plants) then you ate the animal (meatballs), and pretty soon the carbon that was part of grass became part of you.
Part of the carbon cycle is very fast, but the rock-forming part and coal/petroleum/natural gas part take many millions of years.
In the ocean, sediments are the largest reservoirs of carbon--this carbon is not accessible to life. It is slowly turning into rock.
On land, forests are the largest reservoirs of carbon--up to 80% of the aboveground carbon. Most of it is in the tissues of trees. Russia and the Amazon basin together hold about 45% of the world's forest carbon.
On land, peat deposits in the tundras of Siberia and North America, mostly locked up in permafrost, have recently recognized as huge reservoirs of carbon dioxide. These, we fear, will dump much of it into the air as permafrost melts because of global warming. This melt has already begun.

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Greenhouse Earth and Carbon Burial

For the past several hundred years, humanity has been burning fossil fuels at an ever-increasing rate. Coal and natural gas and petroleum are all carbon based compounds. When burned, the carbon grabs oxygen from the air and creates carbon dioxide. Carbon dioxide behaves like glass does in a greenhouse. It lets all the solar radiation in--all the light and infra-red--but it doesn't let the heat bleed off into space very well. In a glass greenhouse, we open windows and turn on fans to get rid of the excess heat, but Planet Earth doesn't have windows and is not equipped with fans. The result is global warming.

Scientists are desperately looking for ways to decrease the carbon dioxide in the atmosphere. But it turns out that we don't know much about the carbon cycle and especially carbon burial. Carbon burial refers to carbon that is buried or sequestered for a time, perhaps a very long time, and is not available to use. We are just learning what the reservoirs of buried carbon are, and where.

The largest reservoir of buried carbon is the ocean. This carbon is part of uncountable billions of living protist shells (tests). These tiny creatures get their carbon from dissolved carbon dioxide in the surface water of the ocean, where water is turbulent enough to soak up gases from the air.When these protists die, their bodies sink, become sediments, and in millions of years, become sedimentary rock, mostly limestones.

We now know that freshwater lakes, reservoirs behind dams, and wetlands bury a lot of carbon in their sediments. We know that the great forests of Earth sequester a whole lot of carbon, but we are busilycutting down the last of them. Much of this wood is being burned, and making carbon dioxide.

Scientists, in their search for solutions to global warming, have discovered that people in "developed" countries do not want to hear about solutions that might change their lifestyles, such as using less fossil fuel, conserving energy and using alternative energy sources, such as wind. So Earth is going to get warmer, the sea levels will rise as the icecaps and glaciers melt, drowning coastal cities, and those ecosystems that survive will radically change.

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The Nitrogen Cycle

Nitrogen Facts

Nitrogen is one of the most abundant elements on Earth
79% of Earth's atmosphere is nitrogen in gaseous form.
No living cell can exist without nitrogen.
But organisms cannot use nitrogen in gaseous form.
Multicellular life (plants, animals and fungi) depend almost entirely on bacteria to obtain (or "fix") nitrogen from the air and transform it into a chemical form that plants can use. See Nitrogen-Fixing Bacteria. In 2005, scientists discovered that some archea microbes can also fix nitrogen.
Some of these talented bacteria interlive with legumes such as beans. These bacteria take nitrogen out of the air in soils.
Other bacteria and archea live freely in the soil, where they process manures and urine, and also help decompose dead plants and animals.
A third kind of bacteria lives in the soil and changes "fixed" nitrogen (a hydrogen compound) into nitrates (oxygen compounds), which plants can use. Without these nitrifying bacteria, agricultural fertilizers cannot work.
In the ocean, cyanobacteria fix nitrogen for marine life. Cyanobacteria also live in lichens. In old growth forests and in deserts, lichens are a primary source of nitrogen. Deserts have living crusts on their surfaces, called cryptobiotic crusts.
Plants assimilate nitrogen from soil, and with it create amino acids and proteins.
Animals get nitrogen from eating plants or from eating other animals

The Nitrogen (N) cycle follows several paths.
N from air
cyanobacteria in desert crusts
animals and/or decomposers
N from air
cyanobacteria in lichens
animals and/or decomposers
N from water surfaces
cyanobacteria in water
animals and/or decomposers
Nitrogen from
soil air
N-fixing bacteria and archea
nitrifying bacteria
animals and/or decomposers
N from dead organisms
decomposers nitrifying bacteria plants animals and/or decomposers

A small amount of nitrogen is fixed by lightning, and volcanoes release some nitrates: both are carried to soils by rain.

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The Sulfur Cycle

Sulfur Facts

Sulfur is essential to all living cells
Bacteria are crucial to sulfur cycling.
Major reservoirs for sulfur are the atmosphere and rock.

The Sulfur Cycle is Complex and takes many paths:

There are many more sulfur compounds in soil than are shown in the illustration.

Plants and microbes absorb sulfur and use it.

Animals get their sulfur from plants.

Burning coal and other fossil fuels release large amounts of sulfur dioxide, which turns into sulfuric acid, which becomes acid rain.

Ocean phytoplankton release sulfur into the air in a form that makes it possible for raindrops to condense and form clouds. These clouds reflect some of the sun's heat and help keep Earth from overheating. See Balancing the Biosphere.

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Explore Further in Cycles

The Season Cycle
Feedback Loops
Micro-Scale Circles and Cycles
Human-Scale Circles and Cycles
Macro-Scale Circles and Cycles
Essay: Life Lives in Circles
  Return to Ecology Index


Copyright © Morning Earth 2007












Copyright © Morning Earth 2005