Antarctic Origins I. Geologic timescale II. Plate Tectonics

Antarctic Origins I. Geologic timescale II. Plate Tectonics

Antarctic Origins I. Geologic timescale II. Plate Tectonics III. Rodinia, Pangea and Gondwana IV. Antarctic Continent and Geology Antarctic ice sheets

form Transantarctic Mtns form Carboniferous Andes Mtns begin

forming, warming Pangea forms, ice sheet over Gondwana Gondwana forms Rodinia fragments Rodinia forms

Stable Isotopes and Radiometric Dating of Rocks Isotopes have the same atomic number but differ in atomic mass Carbon

12 Atomic number Atomic mass

6 C 12 Protons = 6

Neutrons =6 Carbon 13 Atomic number

Atomic mass 6 C

13 Protons = 6 Neutrons =7

Equal number of protons but different number of neutrons Stable Isotopes and Radiometric Dating of Rocks Isotopes are radioactive or stable Radioactive Isotope: changes

atomic number and/or mass over time (decay) Stable Isotope: do not change atomic number/mass and remains stable over time Potassium, uranium commonly used to date older rocks, going back billions of years; carbon only useful for last 50,000 yrs

Three major types of rocks: 1. Igneous: liquid to solid, basalt, granite 2. Sedimentary: accumulation of pieces of other rocks, sandstone 3. Metamorphic: changed rock from melting or pressure, schist, marble

Plate Tectonics (Continental Drift) Plate Tectonics The Earth's lithosphere is broken up into chunks called plates. Oceanic plates are made of basalts (cooled volcanic rock made of silicon, oxygen, iron, aluminum, & magnesium). Oceanic crust is only about 6 kilometers thick. The continental plates are

made of another volcanic type of silicates called granite. Continental crust is much thicker than oceanic crust---up to 35 kilometers thick. Continental plates are less dense than the oceanic plates. The mantle convection causes the crustal plates to slide next to or under each other, collide against each other, or separate from one another in a process called plate tectonics. Plate tectonics is the scientific theory that describes this process and how it explains the Earth's surface geology. http://www.astronomynotes.com

Modern Tectonic Plates and Movements http://commons.wikimedia.org/ Plate boundaries can be: Transform: grinding past each other

Divergent: separating Convergent: colliding Subduction Uplift Plate Tectonics (Continental Drift)

http://www.astronomynotes.com The mid-Atlantic Ridge divergence and subsidence Pingvellir National Park, Iceland Plates are diverging at rate of 3 mm per year, subsidence is at 1 mm per year

Antarctic ice sheets form Transantarctic Mtns form Carboniferous

Andes Mtns begin forming, warming Pangea forms, ice sheet over Gondwana Gondwana forms Rodinia fragments

Rodinia forms SWEAT Hypothesis: Southwest U.S. East Antarctica Connection From Walton text, p. 47 Granite boulder from glacial moraine with isotopic geochemistry similar to those from southwestern Laurentia

From Goodge et al. 2008 Science Antarctic ice sheets form Transantarctic Mtns form

Carboniferous Andes Mtns begin forming, warming Pangea forms, ice sheet over Gondwana

Gondwana forms Rodinia fragments Rodinia forms Carboniferous ice sheet, 300 Ma

Pangea Dry Valleys and Sedimentary Rocks in Transantarctic Mountains Glossopteris Fossil leaves from Mt. Wild, Antarctica

www.teara.govt.nz Also found in India, Australia, Africa, and South America https://wyrdscience.wordpress.com/2011/01/02/fossil-forestsreveal-a-subtropical-antarctica/ Glossopteris leaves from Allan Hills near McMurdo Station

Permian, ~255 Ma Also found in India, Australia, Africa, and South America Ginkgo Tree (Ginkgo biloba), a living fossil

Antarctic ice sheets form Transantarctic Mtns form Extinctions Carboniferous

Andes Mtns begin forming, warming Pangea forms, ice sheet over Gondwana Gondwana forms

Rodinia fragments Rodinia forms Climate warming, lots of vegetation, formation of coal deposits in Antarctica Lystrosaurus, a therapsid dicynodont reptile

Dr. Edwin H. Colbert (1905 2001) First a skeptic of continental drift, found Lystrosaurus in India and Africa In 1960s, went to Antarctica to confirm presence of Lystrosaurus there too

Thrinaxodon, cynodont therapsid from S. Africa and Antarctica Excavating Triassic fossils in Antarctica Fossil Evidence for Plate Tectonics Antarctic ice sheets

form Transantarctic Mtns form Gondwana begins to breakup Carboniferous

Andes Mtns begin forming, warming Pangea forms, ice sheet over Gondwana Gondwana forms Rodinia fragments

Rodinia forms Gondwana begins to separate from Pangea Cryolophosaurus, a crested dinosaur from Jurassic of Antarctica

A Cretaceous Forest in Antarctica Fig. 2.28 Other dinosaurs from Antarctica now include the large, long-necked Sauropods, an ankylosaur and a hadrosaurus (duck-billed dinosaur). Reptiles include pterosaurs, plesiosaurs and mosasaurs (marine)

Gondwana began to break up in the Cretaceous from ~180 mya Finally separation of Antarctica occurred by 32 mya when the tip of S. America separated from the Antarctic Peninsula This is when the current ice sheets on Antarctica today began to form From Walton text, p. 53

Breakup of Gondwana Figure 2.21 in text 180 to 35 mya, Gondwana breakup Shows Antarctic Peninsula as separate plate, moves off the tip of South America by 35-30 mya, opening Drake Passage and forming the circumpolar current that initiated cooling of Antarctica

and formation of ice sheets (p. 56) Microplates positioned themselves within the continent such as the Ellsworth Mountains with their anomalous orientation Antarctica and plate tectonics Rodinia and Antarctica

Note position of Ellsworth Mountains and the rift zone between Marie Byrd Land and the Transantarctic Mountains Dry Valleys Transantarctic Mountains, Victoria Land Coast

Dry Valleys and Sedimentary Rocks in Transantarctic Mountains Sedimentary rocks in Dry Valleys have many fossils Devonian worm burrows, ~400 Ma Antarctic ice sheets

form Transantarctic Mtns form Carboniferous Andes Mtns begin

forming, warming Pangea forms, ice sheet over Gondwana Gondwana forms Rodinia fragments Rodinia forms

While the ice sheets have been present in Antarctica since ~35 Ma, recent evidence suggests a warming phase, or perhaps two warming phases, in the late Miocene (~14 Ma) and early Pliocene (5.3 1.8 Ma). The warming was enough to allow tundra-like growth and dwarf Nothofagus trees to grow in Antarctica as shown by fossils from the Sirius Formation in the Transantarctic Mountains

The climate would have been similar to Greenland today, or the tip of South America in Patagonia http://www.gettyimages.com Fossil Nothofagus leaf from Antarctica compared to modern species

In Miocene (~14 mya), Antarctica remained about 20 C warmer than today, with tundra and beech tree (Nothofagus) forests, similar to Patagonia in South America today. Evidence in Dry Valleys show presence of desiccated aquatic plants, algae, moss, and diatoms Dry Valley discovery Cooling phase occurred after this, interrupted by early Pliocene warming

at 5.3 1.8 Ma Sedimentary rocks also occur extensively on Seymour Island in the Antarctic Peninsula Here, some of the earliest fossil penguins are known from Eocene (~50 mya) rocks

Marine fossils on Seymour Island Penguins evolved in the Southern Hemisphere --earliest penguin-like fossil is from Paleocene of New Zealand A reconstruction of Waimanu tuatahi from Slack et al. (2006).

Two species have been described, the older at 61.6 mya (W. manneringi) Show evolution from a flying ancestor Gap in penguin fossil record of over 10 my, until the Eocene at ~50 mya on Seymour Island --high diversity of penguins, fully formed as modern species

--some quite large: Anthropornis The Seymour Island fossil range from giants like Anthropornis, to numerous species in the same size ranges as today Indicates the niche for penguins was well established in the Southern Ocean by the Eocene Marine ecosystem must have been highly productive and rich

to support all these species. Another gap in fossil record occurs after this time, until the Miocene A penguin humerus from the Prince Charles Mountains, East Antarctica, dated at 10.2 mya. Photo courtesy of Dr. Piotr Jadwiszczak of Bialystok University.

Quiz 1. What is plate tectonics? 2. What is Rodinia and its significance to Antarctic origins? 3. What are Glossopteris, Lystrosaurus and Cryolophosaurus? 4. What caused the breakup of Gondwana and when did Antarctica become fully isolated as a continent?

5. When did penguins first evolve? 6. What are the Transantarctic Mountains and the Dry Valleys?

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