W2.1 Paleomagnetism and Spreading Seas

• German meteorologist and polar explorer • 1880-1930 • Proposed that the present distribution of continents and ocean basins has evolved through time

• Oceans and continents were permanently fixed • The face of Earth had not changed throughout time

• Supercontinent “Pangaea” once existed; Pangaea fragmented in moving continents via continental drift • Fit of continents, past glaciations, climatic belts, fossil distribution, matching geologic units

Fit of continents - shorelines fit roughly while edges of continental shelf fit perfectly Location of glaciations - past polar ice caps evidences (glacier detritus and scars) found away from the poles Paleoclimatic evidence Fossil evidence Rock type and structural similarities

…widespread glaciers forming at high latitudes

Glaciers flow like rivers Sediments of all sizes are shed on the glacier’s surface Sediments are then transported by the glacier and confer it abrasive power

Glaciers act as large-scale conveyer belts that transport sediments downstream, leaving sentiment debris or detritus at the toes of the glacier; this forms moraines

Glaciers depose glacial till - sediment dropped by glacial ice, consisting of all grain sizes, unsorted, unstratified; sediment accumulates beneath glacial ice, at the toe of a glacier, along glacial flanks

a “sandpaper” effect on substrate -striations are caused by large rocks dragging across bedrock -boulders crack crescentic chatter marks into bedrock

If the southern part of Pangaea was over the Permian South Pole, the northern part of Pangaea was over the Equator Evidence is preserved in sedimentary rocks and includes: tropical reefs from shells of marine organisms in clear, shallow, and warm seas; tropical coal from swamps and jungle; sand dunes and evaporites preserved in areas where they could not have formed today.

….the result of large volumes of water evaporating

Identical fossils have been found on widely separated landmasses

• freshwater reptile • Africa and South America

• Subpolar plant with heavy seeds • All

• Non-swimming land-dwelling reptile • India, Antarctica, Africa

• Non-swimming land-dwelling reptile • Africa and South America

• He could not explain why or how the continents moved • Sea-floor bathymetry; distribution of global earthquakes

• Development of echo-sounding (sonar) – sound wave emitted by a ship travels down through the water, is reflected at the sea floor, and returns back up to a receiver on the ship. • This was developed after WWII • Now, we use satellite data

At the ridge axis

Volcanic island chains

….the mid-ocean ridge

• Layer of sediments • Thickest near continents; thinnest or absent at mid-ocean ridge

…at the mid-ocean ridges

…concentrated belts