1. Chapter 17 The History of Life
Photo credit: Jackie Beckett/American Museum of Natural History
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2. 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).
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3. 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.
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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
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Geologic Time Scale
Eras 
Geologists divide the time between Precambrian time and the present into three eras:
Paleozoic Era
Mesozoic Era
Cenozoic Era
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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.
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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
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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).
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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
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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.
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Geologic Time Scale
The basic units of the geologic time scale after Precambrian Time are eras and periods. Each era is divided into periods.
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Geologic Time Scale
Periods 
Eras are divided into periods.
Range in length from tens of millions of years to less than two million years.
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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
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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.
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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.
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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.
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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.
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Coevolution
4. Coevolution
The process by which two species evolve in response to changes in each other over time is called coevolution.
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20. 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.
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21. 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.
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22. 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.
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