PLANET EARTH - THE THIRD MILLENIUMPart 3: Ecosystems on Earth
Of all the planets we know, Planet Earth has the most varied, the most interesting and the most fast-changing ecosystems.
Here are some samples you can visit today.
Lush tropical rain forests like this one in Ecuador, this one in Thailand, or this one in Hawaii are home to what some scientists think is the greatest number and variety of species found anywhere on earth. Many species of plants and animals living in these rain forests have yet to be seen or described by human scientists.
Remote mountain ecosystems like this one in Colorado or this one in Switzerland or this one in China are home to a surprisingly large number of plants and animals, including human beings, all especially adapted for life at high altitudes and low temperatures.
Bleak desert ecosystems like this one in California or this one in Arizona or this one in Morocco are also home to a surprisingly large number of plants and animals, including human beings, all especially adapted to life with scarce water and high temperatures.
Rich grassland ecosystems, on the other hand, like this one in Tanzania, or this one in Kansas, or this one in Mali are home to a much richer variety of plants and animals, especially many large grazing mammals prized by other carnivores, including human beings, for the milk, meat, leather and bone they can provide.
Temperate forest ecosystems like this one in Russia, or similar ones in Minnesota, in Vermont, in China, in Scotland were on the decline a century ago. Now as their 3rd millenium begins these ecosystems are beginning to thrive once more and provide homes to plants and animals that once were near extinction when the original primeval forests were cut down to make way for human farms and cities. Later many of the farms failed, the cities retreated and the land grew back to hardwood and coniferous forests.
Some of these ecosystems have been working together for a very long time. Others are very recent. Like these volcanic Hawaian and Galapagos Islands that rose out of the Pacific Ocean only a few thousand years ago and are now home to many plants and animals found nowhere else on earth.
Also very new are the inland lakes created by glaciers in the recent ice ages on earth. The Great Lakes of the United States, the glacial lakes and ponds of Finland, Sweden and Denmark. Or human-created lakes like this one in Dali, China. Or human-made ponds like this one in Vermont. Lakes and ponds like these are home to plants and animals adapted to life under and above fresh water, a relatively scarce commodity on planet earth.
And finally we come to the largest of the earth ecosystems, the oceans where life began 4 billion years ago and where water is not a scarce commodity. Indeed the salt water of the oceans covers three quarters of the planet and is home to an incredibly large number and amazing variety of living creatures, many of which, like those of the rain-forest, have yet to be seen or described by human scientists.
This especially applies to the particularly large variety of fantastic species recently discovered in the depths of the ocean. These unusual creatures get their life energy not directly from the sun but from the heat coming from the still cooling center of the young planet.
As the 3rd millenium dawns, human beings have invaded and become a key part of all of these natural ecosystems. In addition, they have created whole new ecosystems of their own design.
Agricultural ecosystems, for instance, began about ten thousand years ago. They expanded greatly a few hundred years ago and are common now, taking up about one third of all the land area on earth. Built by humans the agricultural ecosystems are simpler than the natural ecosystems they replace. Rather than being home to a bewildering variety of plant and animal species, the agricultural lands often feature mono-cultures, that is a single plant species dominating large acreages of land. In some places that plant is corn. In others it is rice, or wheat, or potatoes, or apple trees, or tea bushes or coffee trees. In still other places it is grasses which provide ideal grazing land for sheep, or cattle or goats or yaks.
The newest and the fastest growing of all the ecosystems on planet earth are the spectacular human designed cities that are expanding everywhere with ferocious speed. No ecosystem exists independently of the others. Though cities take up only about 2 percent of the actual land area on earth they have influences far greater than their size would warrant. These new cities are also the ecosystems with the greatest dependence on their neighbors.
Each of these ecosystems on earth has its own structure and its own dynamics. Common to all, however, are two important traits.
One. Every ecosystem has a dynamic structure, a unique web of life. The stability of this web comes from the hundreds of thousands of connections of living organisms one to another and to the non-living atoms and molecules at their base.
Two. No ecosystem stands still. Every ecosystem is always changing, is always evolving, is always related in critical ways to all the other ecosystems in the biosphere, and in the 3rd millenium is always changing in response to the most dominant species of the biosphere, Homo sapiens.
Let's look at each of two traits in detail.
One: The life web of an ecosystem is built on the base of a steady energy flow and a continual recycling of matter.
Almost all ecosystems on earth, for instance, (with the notable exception of the newly discovered deep ocean ones) rely on the energy of the sun to power all of the life activities in the system.
The sun's energy is captured by the green plants in the process called photosynthesis. That energy is used by the plants and the animals to power their life activities. In every change of form some energy is lost as random heat. Eventually all of the sun's energy originally captured by the green plants is radiated back into space as useless heat waves. Energy flows through all ecosytems but it cannot be recycled.
But matter can.
All ecosystems on earth are made of matter, that is, of chemicals, of atoms and molecules. Specifically all living things are made of chemicals like carbon dioxide, oxygen, water, proteins, enzymes, hormones, vitamins, nucleic acids and a host of other complex molecules that are themselves built by living tissues from atoms like sulfur, phosphorus, carbon, oxygen, hydrogen, nitrogen and very small amounts of fifteen to twenty of the more common elements of the universe.
These life chemicals are the same in seaweed and in whales, in ants and chimpanzees. In barley and in humans The thing that makes one living thing different from another is the way these chemicals are put together. How this construction is carried out is decided by directions encoded on a long double helix molecule called DNA, deoxyribonucleic acid. This molecule is present in the nucleus of most cells of most living things. Portions of the DNA code are called genes, and right now earth scientists are rapidly deciphering this genetic code of many living organisms, including humans.
When it comes to the complex combinations of living things and non-living environments called an ecosystem, the important thing to note about the life chemicals is that they continually cycle and recycle into and out of all the living creatures of the ecosystem. The carbon atom that was a part of a pondweed today becomes a part of an frog's eyeball tomorrow. The nitrogen atom that was a part of a fish muscle yesterday is part of a cat's paw today. The oxygen atom that came from a tree leaf yesterday is part of a human brain today.
Ecologists, (scientists who specialize in studying ecosystems) often diagram the chemical cycles and the flows of energy through an ecosystem's complex webs and food chains. The particulars of these webs and chains vary considerably in different ecosystems though the general principles are the same in all.
One of the most important of these general principles is homeostasis. This term points to the ability of any living system to respond to life-threatening challenges in certain predictable ways, ways that enhance the system's ability to survive, to stay alive. The basic principle of homeostasis is: with any stress that an organism faces, the organism will respond to counteract, to reduce that stress.
For instance, if the temperature gets warmer, our bodies respond by sweating, by opening up blood capillaries to the surface skin and by making other internal adjustments to take heat away. Vice versa when the temperature gets colder.
Well, all living things, including larger units of living things like ecosystems have homeostatic capabilities. Ecosystems, in other words, like individual organisms tend to stay the same even as they change.
Long-term change (sometimes called evolution) is the second characteristic of all ecosystems. All through four billion years of life history on spaceship earth, ecosytems have been changing, have been evolving.
What is a coral reef today was a volcanic peak yesterday. What is a mountain range today was the ocean floor yesterday. What is a coal mine today was a tropic wetland yesterday.
Individual species of plants and animals have all evolved from some earlier form into the form we find them today. Algae has evolved into oak trees. Dinosaurs have evolved into birds. Amphibians into reptiles. Primates into humans.
Most of these dramatic changes in ecosystems and in individual species have taken place over very long time spans in the past. Today some of these changes, especially the ecosystem ones are taking place much faster than ever before because of the dominance of the most intelligent species, Homo sapiens.
This dominance has caused special problems (and given rise to special opportunities) in the 3rd millenium.
Thousands of chemicals never before experienced in nature have been made by human industrial processes. These chemicals are sent into the air and the water and the soil through smokestacks, landfills, drainage pipes, sprayed from airplanes and spread by tractors. Most of these newly minted chemicals are not needed and usually not taken up and used by living organisms. A few, however, like some lead or mercury or chlorine or iodine compounds, may be taken up by plants or animals and become part of the food chains and the chemical cycles.
Sometimes that can be good for human beings, as when new human-made chemicals, like fertilizers, pesticides and herbicides help farmers protect and grow healthier, more nutritious crops and get higher yields for their labor and on less land. Or when new human-made chemicals help doctors cure disease and promote health.
Some of these chemicals can be useful in one respect and can cause problems in another. Even small amounts of chemicals like dioxin and PCBs and DDT and radioactive iodine once introduced into the natural food chains and chemical cycles may have harmful effects on some members of the ecological community. DDT, for instance, is a chemical that was very useful for people in that it helped to eliminate malaria-carrying mosquitoes in many third world countries and in so doing, saved millions of lives.
On the other hand it was later found to get into the food chain of certain predator birds like the peregrine falcon and the eagle, making their eggshells too thin and drastically reducing their reproductive power. Scientists and environmentalists worried that continued use of DDT could lead not only to the extinction of some bird species, it might have serious though as yet unknown effects on other animal and plant life, including humans. To prevent that from happening DDT was banned in the United States and in many European countries.
Much the same story could be told of other new chemicals already on the market and no doubt will be told of other new chemicals to come in the 3rd millenium.
In the late 20th century some humans in the wealthiest countries let their fear of the bad threaten the progress of the good. They seemed to be unaware of enormous benefits human beings and natural ecosystems have enjoyed from the cornocupia of new chemicals invented in the 20th century--and of the striking progress humans have made in controlling the harmful side effects.
Diseases like tuberculosis, polio, typhoid fever, cholera, malaria, polio and hundreds of others that used to curse and only too often take the lives of hundreds of millions of people around the world have been all but conquered by new chemical drugs and new chemical sanitation methods. As a result all around the world life-threatening pollution has dramatically declined and life expectancies have dramatically increased.
One important measure of this--at the beginning of the 20th century the average person lived about 40 years. Today that figure is over 70 years.
New chemical fertilizers, pesticides and herbicides, new chemical ways of preserving, transporting and serving food, new chemical fuels have helped the average farm family feed a hundred and twenty people in 2000 when it could only feed five people in 1900. Even though the population of humans tripled in the twentieth century, the food supply per person has increased more than the population. As a result there is less starvation and less malnutrition than ever before.
New chemicals have also helped humans control plant and animal diseases in both wild and domesticated ecosystems. They have helped recycle wastes products of plant, animal and human. And perhaps most important of all, they have aided in the scientific research that seeks to understand ecosystems.
Going along with all the good, there have been some harmful side effects. But led by concerned environmentalists and supported by governments, companies and ordinary citizens, the harm has been minimized. As a result of these efforts, the improvement in air, water and soil quality in the richer countries of planet earth was dramatic in the late 20th century. Poorer developing countries like China and India have serious pollution problems as they rapidly industrialize today but even they are less polluted than they were 50 or 100 years ago. And aided by the experience of the wealthier countries, they too are seeing the future as hopeful.
One of the chemical cycling problems that many scientists think is the most serious threat to the ecosystems of the world is what they call global warming.
In the rush to industrialize, countries around the world are using more energy. This energy today is usually obtained by burning fossil fuels in power plants, in automobiles, trucks and aircraft. Waste products of industrial cities and suburban housing areas are burned in incinerators. Agricultural wastes and other industrial activities put more carbon dioxide and other gases like methane into the atmosphere. The increased content of carbon dioxide along with other industrial gases leads to what is called the greenhouse effect. Heat which normally would radiate back to space is instead directed back to earth. The biosphere becomes warmer. How much warmer is a matter of dispute.
Even a few degrees of higher average temperatures on earth would indeed make large differences in rainfall patterns and other ecosystem cycles.
At least three possibilities are there for the 3rd millenium.
Humans may be able to cut back on their production of carbon dioxide and other greenhouse gases by changing energy sources from fossil fuels to renewable fuels or nuclear fuels.
Second. Nature may take care of some of this problem through its homeostatic capabilities. That is, as the carbon dioxide and methane content in the air increases, ecosystems will react to reduce that content. How?
By locking up more of the greenhouse gases in liquid and solid forms in the ocean and earth--called carbon sinks. Humans can help nature build better carbon sinks. We can do this by planting more trees, bioengineering new carbon-eating algae to plant in the ocean, burying more carbon wastes in mummifying landfills, or we can discover other new strategies to take these gases out of the atmosphere and store them in the water of solid portions of earth.
The third possibility is to live with the climate changes. Earth has gone through many climate changes much greater than 3 or 4 degrees in past ages, and ecosystems have adopted. A few hundred years ago the Thames River in England froze in the days of a little Ice Age. England adopted then and could adopt now to a cooling or to a warming.
At this writing it is still unclear whether there will be global warming (and some scientists think it will be global cooling). How successful earthlings of the 3rd millenium will be in coping with climate changes if they do occur is unknown at the present time..
Many humans think the greatest challenge they may face in the 3rd millenium is finding ways to preverse and perhaps to enhance the spectacular plant and animal diversity on Planet Earth. Here there is wide agreement among experts.
In the long four billion history of life on earth many millions of species of plants and animals that once lived on earth no longer do so. These species are extinct.
Today as ecosystems change faster than at most previous times in earth history the rate at which species are becoming extinct has also increased. Scientists, environmentalists and concerned citizens are doing their best today to slow down that rate and to save endangered species like the Giant Panda in China, the Galapagos Tortoise of Equador, the California condor, the Komodo Dragon of Indonesia and the many songbirds and cranes that are devastated as their their habitats are degraded or destroyed on all the earth's continents. Especially threatened are the large and often unknown number of species of plants, and animals in the tropical rainforests of the world. Many of these species will never be known as their habitats are destroyed by human settlers determined to turn these ancient rain-forest ecosystems into modern agricultural lands.
The best way to preserve these species is to preserve their habitats. In some cases this means severely restricting the human presence, keeping more of the earth's surface as a wilderness preserve. In other cases it means using the increased knowledge of ecosystem structure and functioning to creative plan ways for humans and other species to live together in harmony.
A third possibility that is just now receiving much attention is to use the rapidly developing knowledge of genetics, of DNA, of biotechnologies like cloning and new genome banks to preserve the genetic information that makes these species special.
Which brings us back and propels us forward to the most powerful prospect for ecosystem change in the 3rd millenium --the changes that will come with new knowledge of this most basic life structure of all the millions of species of living things on Planet Earth. That is, knowledge of the gene.
How this knowledge will change the ecosystems of earth and how it will change human beings themselves is the subject of the final report of this series. Stay tuned.