Chapter 1: INTRODUCTION, HISTORY OF LIFE (Archaeopteryx from Casiano Zoo)

"If today is a typical day on planet Earth, we will lose 116 square miles of rainforest, or about an acre a second. We will lose another 72 square miles to encroaching deserts, as a result of human mismanagement and overpopulation. We will lose 40 to 100 species, and no one knows whether the number is 40 or 100. Today the human population will increase by 250,000. And today we will add 2,700 tons of chlorofluorocarbons to the atmosphere and 15 million tons of carbon. Tonight the Earth will be a little hotter, its waters more acidic, and the fabric of life more threadbare."   ......   David Orr (1991), "What is Education For?".

Start by reading the environmental review of the United States in the 20th century. It shows the tremendous gains that were made in environmental protection over this time period.  Of course, there have been many losses as well.  But if you ever get discouraged by the difficulty of preserving species and habitats, come back to this review for some encouragement and inspiration!

We live at a critical time for the conservation of biological resources on earth. One third of the world's natural resources were consumed in the period 1970-1995, according to a report by the World Wide Fund for Nature.

In the recent past, the level of biological diversity was the highest the world has ever seen. However, the number of species is not known, even to the nearest order of magnitude. The number of described species is about 1.4 million; but the total is estimated at between 2 and 30 million. It has taken 3.5 billion years for this biodiversity to evolve, and we are rapidly destroying it.  Whereas the natural rate of extinction is estimated at about one species per year, the present rate is estimated at 10,000 times that - about one per hour - and almost all of these losses are caused by human activities. We probably will have lost 1 million species by the end of the century, and several more million will be lost in the first few decades of the next century.

Table 1 gives the number of recorded extinctions between 1600 and 1983. Notice:

- that the total number of recorded extinctions is over 700;
- that over half of these are vascular plants;
- that a very large fraction are island forms, especially with reptiles and birds.

The data are probably most accurate for birds and mammals since these are the most conspicuous of the types of organisms listed. 113 species of birds and 83 species of mammals were definitely lost during this period.
 
  

The number of inconspicuous forms, like insects, that have gone extinct is probably much higher than the number shown on the list. Many of these species are becoming extinct before they are even studied or named by scientists.

The reasons for extinction are changing. In prehistoric times, natural disasters and competition with other species were the main causes. In historic times, overexploitation and exotic species introductions have caused many extinctions. But today, the main problems facing wildlife are destruction of habitat and pollution.

Tropical forest is being destroyed at the rate of 40,000 square miles = an area the size of Ohio, per year. This is mainly due to slash-and-burn agriculture in areas of high population growth, in which small areas are cleared and used for a few years until they become infertile, then more acreage is cleared. Smoke from the fires in Indonesia is visible from space.  About 44% of the original tropical moist forest on the earth is now gone. It has been estimated that between 15 and 20 percent of all species will become extinct by the year 2000 because of the destruction of tropical forests. This rate is about 10,000 times as high as the rate prior to the existence of human beings.

Other habitats are also being destroyed - temperate forests, deserts, wetlands, and coral reefs are all being destroyed at alarming rates, either for profit or to make room for housing, agriculture, ports and other human activities. Damming of rivers has depleted salmon populations in the Pacific Northwest to such an extent that many of the runs are extinct and others have been listed as endangered.

A 1996 study by the World Conservation Union found that 25 percent of mammal and amphibian species, 11 percent of birds, 20 percent of reptiles and 34 percent of fish species are threatened with extinction.  About 10 percent of the world's tree species are in danger of extinction.

The fundamental reason for the degradation and loss of habitat is the explosive growth of the human population. Slide shows how the extinction rate parallels the increase in human population.

Since 1900 the world's population has more than tripled. Since 1950 it has more than doubled, to 5.2 billion. Every year 90 million more people ( = 3x the population of California) are added to the planet. All of these people need places to live, work and play, and they all contribute to habitat loss and global pollution. The chart shows how the loss of two types of forest is related to human population increase.

Our generation is the first one that really became aware of the fact that the human population is causing irreparable damage to the planet - to the air, water and soil of the planet and to its biological resources. Ours is not the first generation to do damage to the planet, but we are the first to realize the extent of the problem.

Ours is the only generation that can prevent a massive loss of biological diversity. Huge losses have already taken place and we will have to make major changes in the way we treat the planet if we are to save it in anything like an intact state.

If we are lucky, ours will be the first generation in which the main principles guiding our governments will not be economic and political systems, but will be learning to live on the planet without destroying it: learning to live, work, grow food, trade, and develop a sustainable way of life that serves the continuing needs of our descendants, and the other species present on earth, as well as ourselves.

Take this course and sign up for the Interdisciplinary Minor in Global Sustainability

(UC students) Join CALPIRG (California Public Interest Research Group) and get experience with activism

If you feel powerless to solve the environmental problems which are the most important problems of our time, get some inspiration from Healing Our World: You Are Not Alone

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A third major group of organisms, called Archaea, consisting of about 500 species but making up about 30% of the biomass on Earth, was not discovered until 1977. They live in the most extreme environments on Earth - the hottest, coldest, and highest pressure environments. Most of the known biomass is in the Antarctic.

Multicellular animals first appeared about 600 million years ago in the early Paleozoic and there was a rapid rise in number of families during the Cambrian and Ordovician. Diversity remained relatively constant (perhaps even declining) up until about 200 million years ago and then it rose again to its current all-time high of close to 800 families.

Biological diversity was dramatically depleted by five mass extinction episodes at the ends of the Ordovician, Devonian, Permian, Triassic and Cretaceous Periods. At each of these times a large fraction of existing species were wiped out, leaving the survivors to repopulate the biological world. The most famous of these was the extinction at the end of the Cretaceous because this ended the age of dinosaurs and made possible the evolution and dominance of mammals. But it was not the most devastating of the mass extinctions.

Many of the important fossils telling the story of the Cambrian explosion were found in a fossil bed in the Canadian Rockies
called Burgess Shale, where both soft- and hard-bodied animals were buried in an underwater mudslide and preserved in water so deep and oxygen-free that they did not decompose. They are described in a book by Steven J. Gould called "Wonderful Life", as well as in the Time magazine article.  Compare pictures of the actual fossils with an artist's rendition of what the animals may have looked like.
 

We will look at the kinds of animals and plants that were present on the earth at different periods, starting with a jump to the Carboniferous because at that time, both plants and animals had moved out on to the land and were beginning to diversify.

Primitive air-breathing fishes, which had two lungs and lobe-like fins, had given rise to the bony fishes, and in these one lung has been lost and the other converted to a swim bladder. They also gave rise to the amphibians, in which both lungs have been retained and the limbs strengthened and specialized for walking. These amphibians, like modern frogs and salamanders, hatched from eggs and spent their larval period in the water as tadpoles, then moved out on to the land as adults. They were the first land-dwelling vertebrates, and some of them were massively built animals two or three feet long. In addition to the primitive amphibians there were also some very primitive reptiles that were totally terrestrial like today's lizards; the egg gave rise directly to a miniature version of the adult, which could survive on the land.

The arthropods of the Carboniferous had also moved onto the land and had in fact taken to the air. Many of the ancient insects were gigantic compared to present day ones, among them mayflies with a 14 inch wing span, and giant six-winged insects, in which the first pair of wings had been already reduced to nubs but not eliminated as they are in all present-day insects. These insects had long sucking mouthparts with which they sucked the juices out of large primitive pine cones. Jarmila Kukalova-Peck calls them the "big suckers of the Carboniferous"! Feeding on these insects were dragonflies with a 30-inch wing span!.

The most successful land animals of the middle Permian were the many kinds of mammal-like reptiles, which were quite varied and included both herbivores and carnivores. Most of them were large, heavy and slow-moving. We can't tell if they were warm-blooded or if they had mammary glands, like true mammals, but they did have a jaw articulation like that found in mammals and they had several types of teeth which is a mammalian feature.

At the end of the Permian, 240 million years ago, huge numbers of animals became extinct. About 96% of all marine animal species and 52% of the families disappeared in the greatest mass extinction the world has ever known. Recent data shows that 8 of 27 orders of insects, 21 of 27 families of reptiles, 6 of 9 families of amphibians and most of the terrestrial plant life disappeared at this time. This happened over a remarkably short period - about 1 million years. The most popular theory is that it was caused by flood volcanism in Siberia - huge continent-sized floods of scorching hot magma, about a mile deep, poured out from fissures in the Earth's crust and spread over the land. The eruption lasted for about a million years, generating about 2 million times as much lava as was involved in the eruption of Mount St. Helens in 1980. This might have generated enough debris to block out sunlight and trigger an ice age, enough sulfuric acid to acidify the oceans, and/or enough CO₂ to cause global warming by a greenhouse effect. Which of these happened, if any, is not known. It took about 100 million years for the species diversity to recover from this mass extinction.
 

The Jurassic and Cretaceous together were the age of giant reptiles. For 150 million years, the dominant vertebrates on the land were the dinosaurs. (By comparison, humans have been on the earth for only about 3 million years).

The dinosaurs are composed of two distinct orders:

The Ornithischians (bird-hip dinosaurs) included the duck-billed dinosaurs or Hadrosaurs; Stegosaurs with their plate-like armour along the back; Ankylosaurs which were heavily armoured and flattened, and the rhinoceros-like horned dinosaurs or Ceratopsians (example - Triceratops).

The Saurischians (lizard-hips) included the Sauropods - gigantic herbivorous dinosaurs with extremely long necks and tails, such as Brontosaurus and Brachiosaurus - the largest terrestrial animals that ever lived; and Therapods - carnivorous dinosaurs with enormous skulls, powerful teeth and ridiculously small front legs, Tyrannosaurus being the best known example but Giganotosaurus was bigger.

The dominant animals of the oceans were the ichthyosaurs, some of which were as large as medium sized whales, the long-necked plesiosaurs and some marine crocodiles. The dinosaurs also took to the air and evolved some spectacular and huge flying reptiles called pterosaurs.  One of them, Quetzalcoatlus, was the largest flying vertebrate the world has ever known, with a 40 foot wing span!

A different, much smaller type of dinosaur is thought to have evolved into the first bird, Archaeopteryx, some time in the Jurassic.

The predominant land plants in the Jurassic were the Cycads, primitive palm-like seed plants.  A few species of cycads still exist in tropical and sub-tropical regions today, and although they are used as ornamental plants some of them are facing possible extinction. Early Cretaceous saw the evolution of flowering plants (angiosperms). The flowers provided a new food source for pollinators, mainly insects, with profound effects on the evolution of those forms.

The end of the Cretaceous saw the culmination of dinosaur evolution. Dinosaurs were more varied and adapted for more different modes of life than any other group, before or since. There were at least 100 species of dinosaurs. Some of them even lived in the Arctic, which was probably a lot warmer than it is now.  They had achieved a level of evolutionary success that would seem to have guaranteed them a permanent place in history, and yet they were soon to disappear entirely from the face of the earth. Several different groups of bird-like dinosaurs had evolved, and all except one - the ancestor of all modern birds - died out at about the same time as the rest of the dinosaurs.