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This volume, aimed at the general reader, presents life and times of the amazing animals that inhabited Earth more than 500 million years ago. The Cambrian Period was a critical time in Earth's history. During this immense span of time nearly every modern group of animals appeared. Although life had been around for more than 2 million millennia, Cambrian rocks preserve the record of the first appearance of complex animals with eyes, protective skeletons, antennae, and complex ecologies. Grazing, predation, and multi-tiered ecosystems with animals living in, on, or above the sea floor became common. The cascade of interaction led to an ever-increasing diversification of animal body types. By the end of the period, the ancestors of sponges, corals, jellyfish, worms, mollusks, brachiopods, arthropods, echinoderms, and vertebrates were all in place. The evidence of this Cambrian "explosion" is preserved in rocks all over the world, including North America, where the seemingly strange animals of the period are preserved in exquisite detail in deposits such as the Burgess Shale in British Columbia. Cambrian Ocean World tells the story of what is, for us, the most important period in our planet's long history.
Author : Stephen Jay Gould Publisher : W. W. Norton & Company Page : 350 pages File Size : 35,82 MB Release : 1990-09-17 Category : Science ISBN : 0393245209
"[An] extraordinary book. . . . Mr. Gould is an exceptional combination of scientist and science writer. . . . He is thus exceptionally well placed to tell these stories, and he tells them with fervor and intelligence."—James Gleick, New York Times Book Review High in the Canadian Rockies is a small limestone quarry formed 530 million years ago called the Burgess Shale. It hold the remains of an ancient sea where dozens of strange creatures lived—a forgotten corner of evolution preserved in awesome detail. In this book Stephen Jay Gould explores what the Burgess Shale tells us about evolution and the nature of history.
*Includes pictures *Includes a bibliography for further reading The early history of Earth covers such vast stretches of time that years, centuries, and even millennia become virtually meaningless. Instead, paleontologists and scientists who study geochronology divide time into periods and eras. The current view of science is that Earth is around 4.6 billion years old, and the first 4 billion years of its development are known as the Precambrian period. For the first billion years or so, there was no life in Earth. Then the first single-celled life-forms, early bacteria and algae, began to emerge. It's unclear where they came from or even if they originated on this planet at all, but this gradual development continued until around four billion years ago when suddenly (in geological terms) more complex forms of life began to emerge. Scientists call this time of an explosion of new forms of life the Paleozoic Era, and it stretched from around 541-250 million years ago (Mya). In the oceans and then on land, new creatures and plants began to appear in bewildering variety, and by the end of this period, life on Earth had diversified into a myriad of complex forms that filled virtually every habitat and niche available in the seas and on the planet's only continent, Pangea. Despite all of the scientific advances made in the past few centuries, including an enhanced understanding of Earth's geological past, very little is known about the planet's early history. It is generally accepted that the planet formed somewhere in the region of 4.5 billion years ago, and at some point, the first life appeared in the form of tiny, single-celled creatures, but scientists are unsure of what this life looked like. One of the problems for those seeking to trace the history of life on Earth is that modern scholars are almost entirely dependent on fossil records, but the earliest types of life left few fossils. The best fossils are formed from the bones and hard body parts of dead creatures, but the earliest types of life were so small that they had no bones or cartilage and thus left no fossils. Thus, even though the Precambrian Period (4,600-541 millions of years ago (Mya)) covers over 80% of the entire history of the planet, scientists have very little idea of what forms of life existed then. Then, as Earth entered the Cambrian Period, there was a relatively sudden increase in life form diversity throughout the oceans. Completely new forms of life, more complex and more diverse than anything that had been seen before, began to spread. This acceleration in the evolution of new forms of life was so dramatic that this has come to be known as the "Cambrian explosion." Although new species in the Cambrian explosion developed almost entirely in the oceans, the land was not entirely devoid of life. Though there were no plants or animals, mats of cyanobacteria and other types of microbes covered large terrestrial areas. Scientists have discovered the tracks of a creature that were left in mud that existed 551 Mya, and those tracks were left by leg-like appendages. Was this a fish-like creature that temporarily invaded the land, or was it something completely different than anything that exists today? There is no general consensus, but the Cambrian Period left a rich fossil record that provides a clear idea of the development of life during this time. At the same time, new discoveries are continually being made, and the more scientists discover about this mysterious period, the more their understanding of ancient Earth changes. The Cambrian Period: The History and Legacy of the Start of Complex Life on Earth looks at the development of the era, the extinction event that preceded it, and how life began to evolve during it. Along with pictures depicting important people, places, and events, you will learn about the Cambrian Period like never before.
Unlike some other reproductions of classic texts (1) We have not used OCR(Optical Character Recognition), as this leads to bad quality books with introduced typos. (2) In books where there are images such as portraits, maps, sketches etc We have endeavoured to keep the quality of these images, so they represent accurately the original artefact. Although occasionally there may be certain imperfections with these old texts, we feel they deserve to be made available for future generations to enjoy.
Until the mid-1980s, AI researchers assumed that an intelligent system doing high-level reasoning was necessary for the coupling of perception and action. In this traditional model, cognition mediates between perception and plans of action. Realizing that this core AI, as it was known, was illusory, Rodney A. Brooks turned the field of AI on its head by introducing the behavior-based approach to robotics. The cornerstone of behavior-based robotics is the realization that the coupling of perception and action gives rise to all the power of intelligence and that cognition is only in the eye of an observer. Behavior-based robotics has been the basis of successful applications in entertainment, service industries, agriculture, mining, and the home. It has given rise to both autonomous mobile robots and more recent humanoid robots such as Brooks' Cog. This book represents Brooks' initial formulation of and contributions to the development of the behavior-based approach to robotics. It presents all of the key philosophical and technical ideas that put this "bottom-up" approach at the forefront of current research in not only AI but all of cognitive science.
The Cambrian Period records one of the most extraordinary transitions in the history of life. Although animals may have first appeared nearly 700 million years ago, with the earliest sponges, their initial diversifications appear to have been modest until a richly diverse fossil fauna appeared abruptly about 170 million years later. In The Cambrian Explosion, Erwin and Valentine synthesize research from many fields to explain why there was such remarkable novelty of animal forms.
When Charles Darwin finished The Origin of Species, he thought that he had explained every clue, but one. Though his theory could explain many facts, Darwin knew that there was a significant event in the history of life that his theory did not explain. During this event, the “Cambrian explosion,” many animals suddenly appeared in the fossil record without apparent ancestors in earlier layers of rock. In Darwin’s Doubt, Stephen C. Meyer tells the story of the mystery surrounding this explosion of animal life—a mystery that has intensified, not only because the expected ancestors of these animals have not been found, but because scientists have learned more about what it takes to construct an animal. During the last half century, biologists have come to appreciate the central importance of biological information—stored in DNA and elsewhere in cells—to building animal forms. Expanding on the compelling case he presented in his last book, Signature in the Cell, Meyer argues that the origin of this information, as well as other mysterious features of the Cambrian event, are best explained by intelligent design, rather than purely undirected evolutionary processes.