How has Plate Tectonics changed the land & seas on Earth's surface?

Answer 1

The middle part of the continents, also known as the craton, has changed little. These are stable and undeformed over time, for the most part. Examples of these areas are in Brazil, Canada, South Africa, Australia, India, and Antartica.

What does change with the land is the position, the arrangement, and the size. Plate tectonics adds (via collisions of terranes) and takes away mass (via rifting) from continental masses. It also places various continents next to each other and moves them around.

The seas are rearranged as well, but the one thing that plate tectonics changes is the volume of the seas. If there is a lot of spreading at the mid ocean ridges (i.e. if it is fast), it causes the seas to float higher, pushing ocean water onto the continents. This happened most recently in the early part of the Cretaceous.

Answer 2

Plate Tectonics is the explanation for the behavior of large portions of the earth's crust in moving past each other and into each other. It has long been observed that the coasts of S.America and Africa fit each other closely and the flora and fauna fossils on various continents seem to match. This was just speculation not science until a mechanism for driving the plates was determined. Sea floor spreading and convection currents in the magma under the crust seem to explain the causes.
When plates slide past each other they cause minimal changes to the land, but the shape of the seas can change considerably. When plates run into each other, one goes underneath, usually and melts causing volcanism on the surface and mountain building. Some times they just collide as India hitting Asia and doing the Himalayas.