25.4

LIFE HAS BEEN INFLUENCED BY GEOLOGIC EVENTS

CONTINTENTAL DRIFT

MASS EXTINCTION

ADAPTIVE RADIATION

Theory of Plate Tectonics• Earth’s crust is broken into plates that float on the hot mantle• Plates move over time – continental drift• Magnetic signal in rock helps geologist track past movements• Typical movement is

10-40 mm per year

SUPERCONTINENT FORMED 3 TIMES• 1.1 BYA, 600 MYA, 250 MYA• Most recent eon – Phanerozic - supercontinent

Pangaea broke into Laurasia and Gondwana• By 65 MYA Laurasia and Pangaea separated into

modern continents

PLATE BOUNDARIES are often geologically active• Transform Boundaries – slide past each other – San Andreas• Divergent Boundaries – move away from each other; ocean-

to-ocean rifting (ex. Mid-Atlantic Ridge) & continent-to-continent rifting (ex. East African Rift Valley)

• Convergent Boundaries – move toward each other; subduction as one plate slides under the other or continental collision (ex. Himalayas)

• Plate boundaries are geologically active – earthquakes, volcanoes, etc.

New Madrid Fault• Divergent boundary – lucky for us the North American Plate did not split!• Deeply buried• Ancient event - still settling down• 4 of largest North American earthquakes

in recorded history (est. magnitude – 8.0) all occurring within 3-month period period between December 1811 and February 1812

This is not on the test! But it’s close to home and I just have to

mention it!

Continental Drift may be SLOW but the consequences are DRAMATIC!• Organisms will adapt, move, or become extinct.• While some species are driven to extinction, species that survive will

have new opportunities.• Habitats change, climate changes, the pattern and diversity of life

changes• Allopatric speciation is promoted – geographic isolation of members

of a population; each group becomes genetically different from the others – new species

***species – organisms can mate and produce fertile offspring (*Spoiler alert – this definition is only a starting point to understanding the definition of species!)

Continental Drift helps explains puzzles about geographic distribution of living things.• How can fossils of the same creature show up on two or

more continents?• I don’t think any of these

animals swam between South America and Africa!

Continental Drift helps explains puzzles about geographic distribution of living things.• Why is Australia’s fauna and flora so different from the rest

of the world?• Why marsupials but no eutherian mammals? (Bats flew in,

humans brought rats and dingo and more)• Marsupials originated in North America and Asia; reached

Australia via South America and Antarctica• Break up of Gondwana separated Australia

Continental Drift helps explains puzzles about geographic distribution of living things.• Break up of Gondwana separated Australia• Marsupials thrived and diversified; if any eutherians were

present they became extinct• Elsewhere most marsupials became extinct and eutherians

thrived• ***Eutherian – placental mammals; nourished before birth

through the placenta• Marsupial – pouched mammals; at birth helpless embryo

must find its way to pouch and continue to grow (for the record marsupials do have a placenta)

MASS EXTINCTIONS• “MASS” means more than 50% of species died• Causes? Climate change (temperature, precipitation, change in

composition of atmosphere, rising and falling sea levels, etc); Geologic events (continental drift, earthquakes, mountain formation, etc.; asteroid impact

• Results? Some species disappear but new species will form new ecological communities by colonizing the new habitats. Ex. adaptive radiation

• 5-10 million years for biological diversity to recover

Fig. 25-14

Tota

l ex

tin

ctio

n r

ate

(fam

ilie

s p

er

mill

ion

yea

rs):

Time (millions of years ago)

Nu

mb

er o

f fa

mili

es:

CenozoicMesozoicPaleozoicE O S D C P Tr J

542

0

488 444 416 359 299 251 200 145

EraPeriod

5

C P N

65.5

0

0

200

100

300

400

500

600

700

800

15

10

20

5 MAJOR MASS EXTINCTION EVENTS

• 2 GET MOST OF THE ATTENTION: PERMIAN PERIOD (end of Paleozoic Era) AND CRETACEOUS (end of the Mesozoic Era)

• PERMIAN – 96% of marine species and large numbers of terrestrial species; perhaps triggered by volcanism – global warming 6o C, drop in oxygen dissolved in the ocean

• CRETACEOUS – 50% of marine species and large numbers of terrestrial species – NOTABLY the dinosaurs; perhaps triggered by asteroid or large comet – debris would block the sun and severely disturb global climate

• Evidence for an asteroid includes presence of iridium in sedimentary rocks suggests a meteorite impact about 65 million years ago

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

Is a Sixth Mass Extinction Under Way?

• 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

ADAPTIVE RADIATION

• process in which organisms diversify rapidly into a multitude of new forms, particularly when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches

Worldwide Adaptive Radiations

• 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

Fig. 25-17

Millions of years ago

Monotremes(5 species)

250 150 100200 50

ANCESTRALCYNODONT

0

Marsupials(324 species)

Eutherians(placentalmammals;5,010 species)

Ancestralmammal

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

Fig. 25-18

Close North American relative,the tarweed Carlquistia muirii

Argyroxiphium sandwicense

Dubautia linearisDubautia scabra

Dubautia waialealae

Dubautia laxa

HAWAII0.4

millionyears

OAHU3.7

millionyears

KAUAI5.1

millionyears

1.3millionyears

MOLOKAIMAUI

LANAI

SILVER SWORD

Remember Darwin’s Galapagos finches?