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 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 Total extinction rate (families per million years): Time (millions of years ago) Number of families: Cenozoic Mesozoic Paleozoic E OS D C P Tr J Era Period 5 C P N

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 6 o 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 Millions of years ago Monotremes (5 species) ANCESTRAL CYNODONT 0 Marsupials (324 species) Eutherians (placental mammals; 5,010 species) Ancestral mammal

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 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 SILVER SWORD

Remember Darwin’s Galapagos finches?