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CONTINENTAL DRIFT Rodina and Pangea

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Breakup of Pangea

225 - 180 mya

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750 mya 550

530

487

422

374260

Rodina a Neoproterozoic 750 mya

b Late Neoproterozoic 550

c Middle Cambrian 530

d Mid-Ordovician 487

e Mid-Silurian 422

f Late Devonian 374

g Early Permian 260

g

G

gf

ed

260

Rodina a b

c

d

e

fg

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Breakup of Pangea

135 - 65 mya

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Present Land - Ocean Distribution

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Creation of the Mid-Atlantic Ridge

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1953

2003

Marie Tharp

Lamont-Doherty Earth Laboratory

Office of Naval Research

“ Bruce Heezen handed me a stack of sound data profile sheets and said Here, do something with these. ”

“ .. this ridge had such a marked feature and we called it the rift valley from the beginning.”

“ I showed this to Bruce, and he didn’t believe me.”

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QuickTime™ and aGraphics decompressor

are needed to see this picture.

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a convection cell in three dimensions

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02_10

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Bottom Topography of the Atlantic Ocean

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Ocean Ridge System

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evidence supporting sea floor spreading

Fossils that lived more than 200 million years ago indicate that Pangea existed and support the supporting the continental drift concept.

Stratigraphy of geological material greater than 200 million years old suggest that the continents were joined prior to that time.

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Very Long Baseline Interferometry [VLBI] measures the time differences in the arrival of microwave signals from radio sources at two or more antennas. In this case the antennas are at Fairbanks and Cape Yakataga. Computer calculations with the time differences can be used to show the movements within the North American [NA] Plate.

This chart plots the relative locations of the antennas during the six year interval 1986 to 1990. Cape Yakataga moved slowly on the Plate toward Fairbanks as the NA Plate was compressed by northward movement of the Pacific Plate. The big change that occurred in 1987 is related to the release of stress by major earthquakes under the Gulf of Alaska. The blue ellipses show the range of error inherent in the measurement of distances.

Radio Astromomy can be used to assess plate motions on earth using the moon as a reflected source of signals.

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A striped magnetic anomaly pattern on the ocean floor and either side of the Mid-Atlantic ridge south of Iceland. The “A” stripe is the youngest ocean bottom and is at the crest. The paired B,B’; C,C’, … stripes were formed at the ridge crest during progress-ively older periods between which the Earth’s magnetic field reversed.

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