Life on Planet Earth: Variety of Microbes, Plants and Animal Species

About the variety of microbes, plants, and animal species to be found on planet Earth.


For sheer numbers of living creatures, one must turn to the microorganisms. "The microbe population on any one of us is undeniably large," Dr. Theodor Rosebury wrote in Life on Man, "numbering vastly more than all the people on earth. Yet they could all be packed into something hardly bigger than an ordinary soup can. They're evidently indispensable to our healthy development and well-being."

Slightly more than a million species of animals are known, and some 300,000 species of flowering plants. There are over 20,000 species of birds, of which about 1,500 fly over North America. More than 5,000 reptiles--turtles, alligators, and snakes--crawl and slither about. One, the tuatara, has been around for 200 million years, unchanged, though there are only a few left on some islands off New Zealand. Another relic of the past is the ginkgo tree, which flourished in the days of the dinosaurs (and was probably part of their diet) and which does very well in the polluted atmosphere of modern American cities. The coelacanth fish, long thought to have disappeared some 70 million years ago, was found to be still flourishing off South Africa, unchanged. The oldest "living fossil" is the lingula, a brachiopod that hasn't changed in the past half billion years.

In the beast-bird-fish or animal-vegetable differentiations, there are some anomalies. The platypus, called an aquatic mammal, breastfeeds its young but lays eggs like a bird. Also, coral, strange underwater polyps--considered holy by religious sea peoples--are both animal and vegetable in their functioning.

The merciless jungle of life-eat-life in the seas is nothing compared to the microworld of tiny creatures a mere fraction of an inch beneath the grass on any peaceful lawn. "Although the soil itself does not give birth to life, it is the incubator for the living world," Peter Farb stated in Living Earth. "The abundance of life to be found in the soil is staggering. The organisms vary from the submicroscopic up to the relatively gigantic earthworm." Earth's cruelest creatures turn out to be not sharks in the sea but tiny nematodes, which have more species than all other kinds of animals combined, and which pursue their prey mercilessly. Our age perhaps should be called "The Age of Nematodes," Donald E. Carr warned in The Deadly Feast of Life. They do at least $2 billion worth of damage to American agriculture. "It is as if we . . . were being invaded by astronomically vast colonies of malign little beings from outer space. And yet it is an ancient animal . . . perhaps eventually it will be found that anything we can do, the nematode will be able to do better."

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