Go to Section:

Concept Map

Evolution of Life

Section 17-2

Early Earth was hot; atmosphere contained poisonous gases.

Earth cooled and oceans condensed.

Simple organic molecules may have formed in the oceans..

Small sequences of RNA may have formed and replicated.

First prokaryotes may have formed when RNA or DNA was enclosed in microspheres.

Later prokaryotes were photosynthetic and produced oxygen.

An oxygenated atmosphere capped by the ozone layer protected Earth.

First eukaryotes may have been communities of prokaryotes.

Multicellular eukaryotes evolved.

Sexual reproduction increased genetic variability, hastening evolution.

Go to Section:

Mixture of gases simulating atmospheres of early Earth

Spark simulating lightning storms

Condensation chamber

Cold water cools chamber, causing droplets to form

Water vapor

Liquid containing amino acids and other organic compounds

Section 17-2

Figure 17-8 Miller-Urey Experiment

Go to Section:

Aerobic bacteria

Ancient Prokaryotes

Ancient Anaerobic Prokaryote

Primitive Aerobic Eukaryote

Primitive Photosynthetic Eukaryote

Chloroplast

Photosynthetic bacteria

Nuclear envelope evolving Mitochondrion

Plants and plantlike protists

Animals, fungi, and non-plantlike protists

Section 17-2

Figure 17-12 Endosymbiotic Theory

Go to Section:

Section 17-3

Geologic Time Scale with Key Events

Glaciations; mammals increased; humans

Mammals diversified; grasses

Aquatic reptiles diversified; flowering plants; mass extinction

Dinosaurs diversified; birds

Dinosaurs; small mammals; cone-bearing plants

Reptiles diversified; seed plants; mass extinction

Reptiles; winged insects diversified; coal swamps

Fishes diversified; land vertebrates (primitive amphibians)

Land plants; land animals (arthropods)

Aquatic arthropods; mollusks; vertebrates (jawless fishes)

Marine invertebrates diversified; most animal phyla evolvedAnaerobic, then photosynthetic prokaryotes; eukaryotes, then multicellular life

Cenozoic

Mesozoic

Paleozoic

PrecambrianTime

Quaternary

Tertiary

Cretaceous

Jurassic

Triassic

Permian

Carboniferous

Devonian

Silurian

Ordovician

Cambrian

1.8–present

65–1.8

145–65

208–145

245–208

290–245

363–290

410–363

440–410

505–440

544–505

650–544

Key EventsEra Period Time(millions of years ago)

Go to Section:

Section 17-4

Patterns of Evolution

Macroevolution refers to large-scale evolutionary patterns and processes that occur over long periods of time. Includes extinction, adaptive radiation, convergent evolution, coevolution, punctuated equilibrium, and changes in developmental genes.

Go to Section:

Extinction• More than 99% of all species that have every lived are now

extinct. • Occur because species compete for resources and

environments change (natural selection).• Mass extinctions wiped out entire ecosytems. Food webs

collapsed and disrupted energy flow through the biosphere.– Most mass extinctions caused by several factors.– Large volcanoes erupting, continents moving, sea levels changing.– Leads to burst of evolution as species fill niches.

Go to Section:

Adaptive Radiation• A single species or a small group of species has evolved,

through natural selection and other processes, into diverse forms that live in different ways.– Darwin’s finches – more that a dozen species evolved

from a single species.– Dinosaurs – ruled earth for about 150 million years.– Mammals – disappearance of dinosaurs lead to adaptive

radiation of mammals.

Go to Section:

Convergent Evolution• Process in which unrelated organisms come to resemble one

another.

• Groups of different organisms, such as mammals and dinosaurs, undergo adaptive radiation in different places or at different times but in ecologically similar environments. Face similar environmental pressures. Natural selection molds different body structures into modified forms (arms and legs into wings and flippers).

• Analogous structures – look and function similarly but are made up of parts that do not share a common evolutionary history.

Go to Section:

Coevolution• Organisms that are closely connected to one another by

ecological interactions evolve together.– Flowers and pollinators

• As evolutionary change in one organism may also be followed by a corresponding change in another organism.

• Analogous structures – look and function similarly but are made up of parts that do not share a common evolutionary history.

Go to Section:

Punctuated Equilibrium• Fossil records show that some organisms evolved gradually

over time.• Others are in equilibrium – have changed little over time.• Long, stable periods are interrupted by brief periods of

more rapid change – punctuated equilibrium. May occur when– a small population becomes isolated from the main part of the

population or a small group migrates to a new environment.– a mass extinction occurs.– Organisms evolve rapidly to fill available niches.

Go to Section:

Section 17-4

Flowchart

that are

can undergo can undergo can undergo can undergo can undergo

in underunderform inin

Species

Unrelated Related

Inter-relationshiops

Similar environments

Intense environmental

pressure

Small populations

Different environments

Coevolution Convergent evolution

ExtinctionPunctuated equilibrium

Adaptive radiation

Videos

Click a hyperlink to choose a video.

Geologic Time

Evolution of Cells

Career links on fossil preparators

Interactive test

For links on the fossil record, go to www.SciLinks.org and enter the Web Code as follows: cbn-5171.

For links on eukaryotic cells, go to www.SciLinks.org and enter the Web Code as follows: cbn-5172.

For links on extinction, go to www.SciLinks.org and enter the Web Code as follows: cbn-5174.

Go Online