Sea floor spreading dating
Although he produced an abundance of circumstantial evidence, his theory met with little acceptance for two reasons: (1) no mechanism for continental drift was known, and (2) there was no way to reconstruct the movements of the continents over time.Keith Runcorn constructed apparent polar wander paths for Europe and North America.Such studies have shown that the strength of the geomagnetic field is alternately anomalously high and low with increasing distance away from the axis of the mid-ocean ridge system.The anomalous features are nearly symmetrically arranged on both sides of the axis and parallel the axis, creating bands of parallel anomalies.marine sediments and absolute age determinations of such bottom material have provided additional evidence for seafloor spreading.As the magma cools, it is pushed away from the flanks of the ridges.This spreading creates a successively younger ocean floor, and the flow of material is thought to bring about the migration, or drifting apart, of the continents.
Research has also revealed that the ridge crests are characterized by anomalously low seismic wave velocities, which can be attributed to thermal expansion and microfracturing associated with the upwelling magma.
Shortly after the conclusion of World War II, sonar-equipped vessels crisscrossed the oceans collecting ocean-depth profiles of the seafloor beneath them.
The survey data was used to create three-dimensional relief maps of the ocean floor, and, by 1953, American oceanic cartographer Earth’s mantle continuously wells up along the crests of the mid-ocean ridges that wind for nearly 80,000 km (50,000 miles) through all the world’s oceans.
(A veritable legion of evidence supports the seafloor spreading hypothesis.
Studies conducted with thermal probes, for example, indicate that the heat flow through bottom sediments is generally comparable to that through the continents except over the mid-ocean ridges, where at some sites the heat flow measures three to four times the normal value.