Chapter 17 The History of Life Photo credit: Jackie Beckett/American Museum of Natural History Copyright Pearson Prentice Hall

Fossils and Ancient Life Paleontologists – scientists who collect and study fossils. Fossil record – information about past life including how different groups of organisms have changed over time. Over 99% of all species that have lived on Earth have become extinct (the species has died out). Copyright Pearson Prentice Hall

Geologic Time Scale Geologic Time Scale Paleontologists use a scale called the geologic time scale to represent evolutionary time. Scientists first developed the geologic time scale by studying rock layers and index fossils worldwide. An index fossil is a species that is recognizable and that existed for a short period but had a wide geographic range. The basic divisions of the geologic time scale are eras and periods. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale Precambrian Time Geologic time begins with Precambrian Time, which covers about 88% of Earth’s history. The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods. Vendian 650–544 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale Eras  Geologists divide the time between Precambrian time and the present into three eras: Paleozoic Era Mesozoic Era Cenozoic Era Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale Paleozoic Era The Paleozoic began about 544 million years ago. Many vertebrates and invertebrates lived during this time. There was a diversity of marine life. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale Permian 290–245 Carboniferous 360–290 Devonian 410–360 The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods. Silurian 440–410 Ordovician 505–440 Cambrian 544–505 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale Mesozoic Era The Mesozoic began about 245 million years ago. Divided into the Triassic, Jurassic, and Cretaceous periods. Dinosaurs lived during this time. Mammals began to evolve during this era. Flowering plants appeared. The Cretaceous period ended with a mass extinction (more than half of all plants and animals were wiped out). Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale Cretaceous 145–65 Jurassic 208–145 The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods. Triassic 245–208 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale Cenozoic Era The Cenozoic (Age of Mammals) began about 65 million years ago and continues to the present. Mammals became common during the Cenozoic and adapted to live in various environments. Divided into Tertiary and Quaternary periods. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Geologic Time Scale Periods  Eras are divided into periods. Range in length from tens of millions of years to less than two million years. Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall Macroevolution: large-scale evolutionary patterns/processes that occur over long periods of time. Six important topics in macroevolution are: extinction adaptive radiation convergent evolution coevolution punctuated equilibrium changes in developmental genes Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Extinction 1. Extinction More than 99% of all species that have ever lived are now extinct. Provided ecological opportunities for organisms that survived. Resulted in bursts of evolution that produced many new species. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Adaptive Radiation 2. Adaptive Radiation Adaptive radiation: a single or small group of species evolves into several different forms that live in different ways. Ex. Darwin’s finches (more than 12 species have developed from 1). The disappearance of dinosaurs resulted in the adaptive radiation of mammals. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Convergent Evolution 3. Convergent Evolution The process by which unrelated organisms come to resemble one another is called convergent evolution. Convergent evolution has resulted in sharks, dolphins, seals, and penguins. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Convergent Evolution Structures that look and function similarly but are made up of parts that do not share a common evolutionary history are called analogous structures. A dolphin’s fluke and a fish’s tail fin are analogous structures. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Coevolution 4. Coevolution The process by which two species evolve in response to changes in each other over time is called coevolution. Copyright Pearson Prentice Hall

Punctuated Equilibrium Pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change. Whether it is gradual or punctuated, evolution has often proceeded at different rates for different organisms at different times during the history of life on Earth. Biologists have considered two different explanations for the rate of evolution, as illustrated in these diagrams. Gradualism involves a slow, steady change in a particular line of descent. Punctuated equilibrium involves stable periods interrupted by rapid changes involving many different lines of descent. Copyright Pearson Prentice Hall

Developmental Genes and Body Plans Changes in genes for growth and differentiation during embryological development could produce changes in body shape and size. Small changes in the activity of control genes can affect many other genes to produce large changes in adult animals. Small changes in the timing of cell differentiation and gene expression can make the difference between long legs and short ones. Copyright Pearson Prentice Hall

Developmental Genes and Body Plans Evolution of Wings in Insects Ancient Insect Two Types of Modern Insects Some ancient insects, such as the mayfly nymph (top), had winglike structures on many body segments. Modern insects have only four wings or two wings. Changes in the expression of developmental genes may explain how these differences evolved. Copyright Pearson Prentice Hall