Chapter 7: Changing Continents and Climates

19 th Century Geology Law of Superposition – 19 th century geologists assumed that strata lower in the stratigraphic exposure were older than the overlying strata Law of Uniformitarianism – assumes that processes that weathered, eroded, and deposited rock in the past were the same as those operating today These laws used to develop geologic time scale

Alfred Wegener 1912 Theory of Horizontal Displacement of the Continents – similarities between Atlantic coastlines Theory of Continental Drift ( ) –Crust of continents composed of relatively light rocks. Ocean floors largely composed of dense basalts. Lighter continental rocks could float on viscous mantle of Earth and override oceanic crust

–Permian glacial deposits in Brazil, South Africa, India, and Australia – indicates that tropical areas once glaciated, so they must have been close to the poles at one time –Similarities in the shapes of continents, their geology, and fossils suggest closer proximity in the past –Geodetic measurements of latitude and longitude of Greenland indicated westward movement of the landmass –Continental Drift led to Plate Tectonics Alfred Wegener

Pangaea Gondwanaland – Africa, South America, Australia, Antarctica, and India Laurasia – North America, Europe, and Asia Pangaea formed 195 mya – began to break up 180 mya with formation of Atlantic Midoceanic Ridge Alfred Wegener

Figure 7.3

Vindication – Alfred Wegener Lystrosaurus – Triassic reptile –fossils found in Antarctica, Africa, and India – Antarctica must have been warmer in the past

Galaxioidea – freshwater fish family – found in southern South America, South Africa, Australia, and New Zealand – must have been connected in the past WWII – sea floor mapping by submarines Vindication – Alfred Wegener

Paleomagnetism – ancient igneous rocks are little compasses iron or titanium point to their magnetic north compare this to current magnetic north to determine where continents used to lie

Figure 7.6

Glaciation Radiocarbon dating – based on measuring the amount of the radioactive isotope carbon 14 found in plant and animal remains Greenland ice cores extend 100,000 years Antarctic ice cores extend 400,000 years Ice cores provide record of atmospheric chemistry 18 O isotopes deposited during warmer times – 16 O isotopes deposited during cooler times

Figure 7.7

Figure 7.9 Relationship between atmospheric temperature and 18 O isotopes