Physical Geology: GEOL 107

GEOL 107: Physical GeologyDr. Lijun Liu1AnnouncementsSyllabus quiz due today, 10 pm.

Chp 3 quiz due Monday, 11 am.

3Review of last lectureWhat is physical geology

Formation of Earth

Moon forming eventWhich is true about Earths structureThe deeper into the Earth, the stronger the material becomes.There is a giant bar magnet inside the Earth, to generate the geomagnetic field.The asthenosphere is made of magma, as is why material in this layer could flow.The only common interface in both the compositional and rheological layering is the core-mantle boundaryI-clicker question:The lithosphere is made of____Continental crust and asthenosphereBasaltic rocksThe outermost compositional layer of EarthCrust and the uppermost mantleI-clicker question:

NAMSAMEURASIAFRAUSDo you think there were any spatial relations between different continents?From this map, we can infer thatN. America and Australia never stayed next to each otherAfrica and S. America were never togetherAfrica and N. America could have been connected in the pastAntarctic and Asia couldnt have been connectedI-clicker question:

7This topography map is full of information. What could you tell about the past evolution of Earth?The Himalaya Mountains stay in the interior of a plateThe high topography regions (brown color) have stayed the same since the very early history of Earths evolution.The two N-S oriented ridges in the Indian Ocean suggest India moved northward during the pastThe roughness in the seafloor results from rapid deep ocean circulations

64208-2-4-6-8Elevation (km)

Wegeners hypothesis (1912): Continental DriftThe supercontinent PangaeaFigure 3.1Why could Wegner make this hypothesis?9Continental Drift

Alfred Wegener, 1880-1930In 1912, Wegener hypothesized that the continents were slowly drifting around at Earth surface.

Wegener also presented various evidence to support his hypothesis

Evidence for Pangaea (1)S. AmericaAfricaFit of the Continents

Late Paleozoic (~300 Ma) Glacial DepositsFigure 3.3Evidence for Pangaea (2)

Consistent Ice Sheet FlowFigure 3.3Evidence for Pangaea (2)Tropical Climate Indicators

Fossilized Marine ShellsSalt DepositsEvidence for Pangaea (3)

Continuous Climate BeltsFigure 3.3

Distribution of FossilsFigure 3.3Mesozoic: 250 65 MaEvidence for Pangaea (4)

Paleozoic mountain belts540 250 MaEvidence for Pangaea (5)

Distinctive rock belts2500 540 Ma> 2500 MaEvidence for PangaeaFit of the ContinentsPast Ice Sheet with consistent flow directionsDistribution of coal swamps and desertsSimilar fossil record on different continentsMountain belts on both sides of ocean basins

Wegeners supercontinent PangaeaFigure 3.1~300 MaA great discovery purely based on correlationsWhy could Wegner make this hypothesis?2021Question: why continents move?Oceanic crust: thin & denseContinental crust: thick & light

Doesnt work; Centrifugal and tidal forces not strong enoughContinental crust plows through oceans?Continental Drift Rejected!There was no proper physical mechanism that Wegener proposed to move relatively light continents through heavy ocean basins.

Wegeners proposition went to dormancy, and he died in a field trip in 1930.