Chapter 17 Notes

I. Continental Drift A.Early mapmakers noticed matching coastlines B.Single landmass theories 1.Suess-(late 1800s) Austrian geologist theorized that the southern continents were once joined in a body called Gondwonaland 2.Wegener-(1912) German scientist who proposed that all continents were once joined in a body called Pangaea

C. Evidences for plate tectonics 1. Rock formations with shared rock types, ages, and orientations a) Appalachian Mountains with Greenland and Europe b) South America and Africa

Appalachian Mountains and the Caledonide Mountains in Greenland & Europe

2. Fossil evidences: a) Mesosaurus, a freshwater animal found on widely separated continents

b) Labyrinthodont; land-dwellers found on widely separated continents.

c) Glossopteris; fossil seed fern found on widely separated continents

3. Climate evidence a) Coal deposits found in Antarctica. Coal forms in warm, tropical areas.

Climate Evidences con’td b) Glacial deposits and striations (long parallel scratches) found in the Sahara Desert.

D. Wegener’s theory was rejected by the scientific community. Why? 1. He had no explanation for HOW the continents could have moved. 2. Even if he could have explained that, the question still remained-How could continents move without breaking apart?

II. Seafloor Spreading A.Technology 1.RADAR (Radio Detection and Ranging) and SONAR (Sound Detection and Ranging) were developed during WWII. After the war ended, they were modified for scientific use. 2. Magnetometer can detect very small changes in magnetic fields. Magnetic field reversals were detected worldwide.

A.Topography of the Ocean Floor 1.No longer thought to be just a wide, flat plain 2.Underwater trenches (deep enough to submerge Mount Everest!!) and mountain chains that encircle the entire earth were discovered. B.Rocks & Sediments 1.Old rocks were found near the continents, young rocks near the ocean ridges 2.Thick sediments were found near continents, almost none near the ocean ridges at center of oceans.

D. Magnetism 1. The use of magnetometers during repeated crossings of the worlds’ oceans revealed a pattern of magnetic reversals over time. 2. Magnetic Symmetry – Each side of the mid-ocean ridge is a mirror image of the other. Magnetic stripes parallel to the ridge can be paired with magnetic reversals discovered in rocks on land. This helps to determine the ages of seafloor rocks.

III. Plate Tectonics & Boundaries A.Plate Tectonics – a new theory emerged which combined Wegener’s old ideas of Continental Drift and the new theory of Seafloor Spreading. B.Data began to emerge about three types of plate boundaries (edges.) They are: 1.Divergent 2.Convergent 3.Transform

A.Divergent Boundaries 1.Plates move apart 2.On land, this is called a Rift Valley Example: African Rift Valley 3.Under the sea, it is known as a Mid-Ocean ridge. Example: Mid-Atlantic Ridge

B. Convergent Boundaries – collisional 1. Continent – continent Mountain building Example: India and Eurasia colliding is still building the Himalayan Mts. 2. Continent – oceanic Violent volcanoes and deep-sea trenches (Subduction) Example: Pacific plate and North America colliding to produce Mt.St.Helens, Ranier, Hood, etc in the pacific northwest 3. Oceanic – oceanic Produces underwater volcanoes Example: Pacific plate and Japan

C. Transform Boundaries Plates slide past one another. Example; San Andreas Fault in California