Sea floor spreading dating
These curves diverged, but could be reconciled if it was assumed that the continents had been in contact up to 200 million years ago.
This provided the first clear geophysical evidence for continental drift.
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.
The continents bordering the Atlantic Ocean, for example, are believed to be moving away from the Mid-Atlantic Ridge at a rate of 1–2 cm (0.4–0.8 inch) per year, thus increasing the breadth of the ocean basin by twice that amount.
New oceanic crust is magnetized as it forms and then it moves away from the ridge in both directions.Paleomagnetism continues to extend the history of plate tectonics back in time and are applied to the movement of continental fragments, or terranes.