When you observe this Earth we live on, you see that it is a wondrous place that meets all your needs in the most perfect way. The bread, cheese, honey, meat, fruits and vegetables you eat with their many different flavors; the water, milk and fruit juices you drink; the air you breathe; your furniture and other objects crafted of wood and glass and plastic; the articles of clothing you wear; fossil fuels such as gasoline, coal and natural gas that provide your heating, transport and all kinds of energy requirements; the cats, dogs, trees and flowers you see when you are out walking; the medicines and remedies you take when you are ill; animals and plants with their totally different structures and features, the dazzling colors and perfect systems that you see on the television; butterflies, birds and fish; all matchless works of art; insects living in unspoiled forests and unexplored regions that you see photographed in magazines and newspapers; roses, lilacs, orchids, lavenders and violets, with their stunning perfumes and appearances; even this page that you are reading at the moment...
At first, you may not see any connection between all these objects, but take a second look. You will then realize that all living things—as well as man's handiwork— are the result of a glorious variety on Earth. The millions of species of living animals, plants and members of the other three kingdoms (fungi, Protista and Monera) that exist mostly at the microscopic level, constitute an ideal environment for all of your human needs to be met.
The Earth hosts millions of living species, from bacteria and viruses too small to be seen with the naked eye to giant Sequoias, from minuscule beetles and midges to enormous whales. Some 2 million different living species have been identified to date, although it is estimated that there are actually many more. There is practically no place on Earth that is completely devoid of life. Wherever you may go, from thousands of meters beneath the sea surface to the highest mountain peaks, from the burning deserts to the icy poles, you will encounter a variety of living species. The many different environments on Earth offer very different conditions: Oceans, seas, lakes, rivers, coral reefs, marshes, forests, meadows, deserts, rocky outcrops... No matter how different their conditions may be, all play host to a wide range of life forms.
Everyone knows that our a planet contains a teeming variety of life. Yet most people may never have reflected on this astonishing state of affairs, nor considered the great importance of this variety and how it must have come into being. They may never have thought of the need to reflect on these things. Now, putting aside for a moment the perspective stemming from familiarity, try to imagine a world without all these living things you know about.
First, picture an Earth in which there are no terrestrial or marine plants, no forests, and no trees. You will soon come to an obvious conclusion: Were it not for plants that perform photosynthesis every day, the oxygen essential for life would not be replenished, and for that reason, there would be no life on Earth apart from a few bacteria.
And what would the world be like without bacteria, whose species are estimated to number between 300,000 and 1 million, most of whose scientific names are known only to experts? Yet even if we have very little knowledge about bacteria, members of a different world that we cannot see, there is still one indisputable fact: Life without them is inconceivable. Because the production of a large part of the oxygen in the atmosphere, its elemental cycles, the cleansing of the Earth and the breakdown of dead organisms into re-usable substances and many other vital processes are all due to these microscopic creatures.
Vertebrates, mollusks, arthropods, crustaceans and dozens of other plant and animal groups play an important role in the ecological balance in the seas, forests and land. Were any of these to be absent, the processing of dead organisms into new sources of food would be interrupted, the