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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; oceanto-ocean rifting (ex. Mid-Atlantic Ridge) & continent-tocontinent 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
December 1811 and February 1812
This is not on the test! But it’s
close to home and I just have to
mention it!
period between
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
800
700
15
600
500
10
400
300
5
200
100
0
Era
Period
542
E
O
Paleozoic
S
D
488 444 416
359
C
Tr
P
299
251
Mesozoic
C
J
200
145
Time (millions of years ago)
Cenozoic
P
65.5
N
0
0
Number of families:
Total extinction rate
(families per million years):
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
Ancestral
mammal
Monotremes
(5 species)
ANCESTRAL
CYNODONT
Marsupials
(324 species)
Eutherians
(placental
mammals;
5,010 species)
250
200
100
150
Millions of years ago
50
0
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
SILVER
SWORD
Close North American relative,
the tarweed Carlquistia muirii
Dubautia laxa
KAUAI
5.1
million
years
MOLOKAI
OAHU
3.7 LANAI
million
years
1.3
MAUI million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Remember Darwin’s Galapagos finches?