Plate Tectonics

Events

Pellegrini: theorised possibility of continental drift

1858

Suggested all continents were once joined during the Pennsylvanian Period. Supported by the fact he found identical plant fossils in Europe and US

Wegener: Continental Drfit

1912

Hypothesised that the landmasses are dynamic, building upon the ideas of Pellegrini.
He had a PhD in Astronomy, not a geological background thus seen as a maverick and outsider.
His theory lacked evidence, especially a proposal of the dynamic mechanism.

Origins of Continents and Oceans translated into English

1928

Holmes: mechanism

1929

By pioneering the use of radiometric dataing of minerals, enabled him to grasp the mechanical and thermal implications of mantle convection, contributing to the acceptance of plate tectonics theory. He proposed the earths mantle contained convection cells that dissipated radioactive heat from the core, thus moving the crust. Including the concept of seafloor spreading

Hess: proposed seafloor spreading

1962

According to Hess, seafloor was created at mid-oceanic ridges by the convection of the earth's mantle, pushing and spreading the older crust away from the ridg

Wilson: Hot-spots

1963

Hot-spot theory explained anomalies which undermined the plate tectonics theory (plume from core). Also recognised transform plate boundaries,

Vine & Matthews: Mid-Atlantic Ridge, first evidence of seafloor spreading

1963

If Hess was correct then the rocks surrounding the Mid-ocean ridges should show symmetric patterns of magnetization reversals using newly collected magnetic surveys (as geomagnetic reversal occur, the crust on either side of the ridge will contain a record of remnant magnetizations of normal or reversed magnetizations in comparison to the current geomagnetic field.)

The Glomar Challenger

1968

Drilled up rocks from seabed to determine their age. Consolidated the theory that youth of rocks is positively correlated with distance from Mid-Atlantic Ridge (new material being created symmetrically)

McKenzie: Earths divided into Plates

1968

Tied all the loose strings together, offering a complete model of the earth. where the earth is divided into six major lithosphere plates that floor above the mantle, convection currents fuel their movement.

Apparent Polar Wandering

1970

"apparent polar wander paths" could be used to reconstruct the past motions of the continents, using the assumption that the pole was always in about the same place (except during reversals).
A magnetometer can measure the angle between the direction of the Earth's magnetic field and horizontal. This is called the magnetic inclination. Because the Earth is a round body in a dipole field, the inclination is directly dependent on latitude. In fact, the tangent of the angle of inclination is equal to twice the tangent of the magnetic latitude, which is the latitude at which the permanently magnetized rock was sitting when it became magnetized. Therefore, given knowledge of your present location and a magnetometer reading of the inclination of your geologic item of interest, such as a basalt flow, you can calculate the magnetic latitude at the time of its formation, compare it to your present location, and determine how many degrees of latitude your present location has moved since that rock cooled.