The History of Life on Earth

Page
7

The presence of iridium in sedimentary rocks suggests a meteorite impact about 65 million years ago.

The Chicxulub crater off the coast of Mexico is evidence of a meteorite that dates to the same time.

Massive Meterorite Impact Evidence

Slide 44

Evidence of Meteroite Impact

NORTH

AMERICA

Chicxulub

crater

Yucatán

Peninsula

Slide 45

Is a Sixth Mass Extinction Under Way? Consequences …

Scientists estimate that the current rate of extinction is 100 to 1,000 times the typical background rate.

Data suggest that a sixth human-caused mass extinction is likely to occur unless dramatic action is taken.

Mass extinction can alter ecological communities and the niches available to organisms.

It can take from 5 to 100 million years for diversity to recover following a mass extinction.

Mass extinction can pave the way for adaptive radiations.

Slide 46

Adaptive Radiations - New Environmental Opportunities …

Adaptive radiation is the evolution of diversely adapted species from a common ancestor upon introduction to new environmental opportunities.

Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs.

The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size.

Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods.

Slide 47

World-Wide Adaptive Radiations

Millions of years ago

Monotremes

(5 species)

250

150

100

200

50

ANCESTRAL

CYNODONT

0

Marsupials

(324 species)

Eutherians

(placental

mammals;

5,010 species)

Ancestral

mammal

Slide 48

Regional Adaptive Radiations

Adaptive radiations can occur when organisms colonize new environments with little competition.

The Hawaiian Islands are one of the world’s great showcases of adaptive radiation.

Slide 49

Hawaiian Islands -- Regional Adaptive Radiations

Close North American relative,

the tarweed Carlquistia muirii

Argyroxiphium sandwicense

Dubautia linearis

Dubautia scabra

Dubautia waialealae

Dubautia laxa

HAWAII

0.4

million

years

OAHU

3.7

million

years

KAUAI

5.1

million

years

1.3

million

years

MOLOKAI

MAUI

LANAI

Slide 50

Major changes in body form result from changes in the sequences and regulation of developmental genes