The scans for MH370 revealed that the ocean crust rises and falls in waves that start at the Southeast Indian Ridge and continue outward. The ridge spreads about 35 millimeters in opposite directions every year, and the wave crests, where crust grew faster, are more than 100 kilometers long and repeat every 10-14 kilometers. The researchers estimated when each wave formed by comparing the bathymetry maps to independent measurements and models of the crust's magnetic field. ...Crustal rocks record the polarity of Earth's magnetic field as they form, allowing scientists to trace the age of different sections of ocean crust....