- The document discusses how the theory of continental drift evolved into the theory of plate tectonics through various geological discoveries in the mid-20th century. - Key evidence included fossil distributions, glacier patterns, and the matching shapes of continents on opposite sides of the Atlantic. However, the mechanism for continental drift was unknown. - In the 1950s-60s, studies of seafloor topography, magnetism in oceanic rocks, and seismic activity revealed processes of seafloor spreading at mid-ocean ridges and tectonic plate movement. - Harry Hess and Robert Dietz combined these findings into the hypothesis of sea floor spreading, providing the missing mechanism that led to the new theory of

1. How the theory of Continental Drift became the theory of Plate Tectonics

2. Evidence for Continental Drift Fossil Evidence Glacier & Climate Evidence Continental Fit Structural & Strata Evidence

3. Continental Drift The evidence suggested that the continents were once all together in a super-continent called Pangea And that the continents were not always located in the same place on the globe. http://www.knowledgerush.com/kr/encyclopedia/Pangea_supercontinent/

4. Drifting Continents Alfred Wegener and his supporters thought the continents were moving about the oceans like big rafts but couldn’t explain how this happened. http://tea.armadaproject.org/deaton/12.6.2004.html

5. New Information After Alfred Wegener died in 1930, Continental Drift Theory was mostly disregarded. . . No one knew that the key information explaining how the continents to move would lie in a remote and vast part of the world that was still almost entirely unexplored.

6. Secrets in the Ocean www.tripadvisor.com/LocationPhotos-g255055-Au...

7. Secrets in the Ocean Topography Most people thought the ocean floor was a flat plain except for one set of mountains. Laying the trans-Atlantic telegraph cable in the late 1850’s revealed there was some kind of high ridge in the mid-Atlantic During World War II seafloor topography was mapped with sonar.

8. Seafloor Map http://www.pacificislandtravel.com/nature_gallery/platetectonics.html

9. Secrets in the Ocean Magnetism Magnetism in Rocks When lava cools, minerals get “frozen” in what ever position they were last in. The Earths magnetic field affects some minerals so that they line up parallel to it. http://www.tulane.edu/~sanelson/geol111/pltect.htm

10. Measuring Magnetism Magnetometers were used for minesweepers in World War II. By the 1950’s scientists used magnetometers to study continental and ocean rocks to study paleomagnetism . http://ofgs.ori.u-tokyo.ac.jp/okino/okino-res-e.html

11. Magnetic Polarity Time Scale Paleomagnetic studies showed that the Earth’s magnetic field had switched many times through geologic history http://roma2.rm.ingv.it/en/themes/17/magnetostratigraphy

12. Magnetic Stripes on the Ocean Floor http://pubs.usgs.gov/gip/dynamic/magnetic.html

13. Secrets in the Ocean Structure of the ocean floor Seismic studies tested the structure of the ocean crust. http://www.rigzone.com/training/insight.asp?i_id=303

14. Secrets in the Ocean Structure of the ocean floor These studies revealed that about 100 km below the hard surface, the Earth got softer. http://www.physicalgeography.net/fundamentals/10h.html

15. Secrets in the Ocean Earthquakes Scientists found that earthquakes in the ocean were centered at the seafloor ridges. http://beyondpenguins.nsdl.org/issue/column.php?date=December2008&departmentid=professional&columnid=professional!science

16. Secrets in the Ocean Heat The flow of heat through the ocean floor was discovered to be strongest/hottest at the ridges http://eqseis.geosc.psu.edu/~cammon/HTML/Classes/IntroQuakes/Notes/plate_tect01.html

17. So what? None of the scientists who discovered these things thought they had anything to do with the theory of Continental Drift.

18. So What? Separately Harry Hess and Robert S. Dietz saw some of this information and had the interesting idea which they called Sea Floor Spreading. Harry Hess Robert S. Dietz http://oceanexplorer.noaa.gov/history/electronic/1946_1970/media/dietz.html http://www.amnh.org/education/resources/rfl/web/essaybooks/earth/p_hess.html

19. Sea Floor Spreading Sea Floor Spreading was the key to the new theory of Plate Tectonics. Alfred Wegener’s evidence, when put together with sea floor spreading went a long way to convince people that the continents, not only could but did move apart from each other—not as huge rafts, but as passengers on tectonic plates.

20. Morley-Vine-Matthews Hypothesis 1966 Fred Vine and Drummond Matthews pulled it all together in publications in 1966 Morely’s article was rejected--looking back some say that it was the most significant piece of scientific writing ever rejected from a journal. Lawrence Morely Fred Vine, Drummond Matthews and Dan McKenzie

21. A new theory is born By 1967 Sea Floor spreading was finally accepted by most geologists and the theory of Plate Tectonics was born. http://spot.pcc.edu/~aodman/GS%20107%20web/earth,venus,mars/earthmarsvenusindex.htm