Forces of creation
* Volcanism. Volcanoes and similar tectonic activity can produce surprisingly large landforms - take a look at Japan and Hawaii. This is most common in ocean subduction zones but it may be possible to build more land this way above the sea.
* Convergent plate movement. You can get some pretty large mountain ranges by smushing together existing chunks of land - take, for example, the Tibetan Plateau, home to the world's tallest mountain. This is related to continental drift, as are many ideas presented here, but it is a complicated phenomenon that will produce many results.
* Matter from space. This not likely, and it's really only happened on a large scale once, but a planetary-sized event could send a whole lotta stuff down. This also counts as destructive.
* Living things. Life has completely changed the Earth's atmosphere (also building up massive piles of iron sediment in the process), created massive deposits underground, massive deposits aboveground, and changed the color of the planet as seen from space (hint: it's green now). It is reasonable to believe similar changes may occur in the future.
Forces of destruction
* Weathering and erosion. Wind, water, plants, and other phenomena can break down the land, often in dramatic ways. This has given us the Grand Canyon, among other things.
* Subduction. 208
The continents don't just drift! Material can be re-absorbed over time, as it has been for billions of years.
* Glaciers. Ice ages are unpredictable and poorly understood. If one were to occur, we could see glaciers carving up the terrain.
Neutral
* Rising sea levels. If human emissions continue, the climate will continue to change. The poles will shrink, and the sea will slowly overcome the land. There are some pretty good simulators for this.
* Sinking sea levels. If the Earth cools, water will be trapped in ice, lowering the sea level.
* Transform plate movement. This can shift the locations of land masses greatly over time.
* Divergent plate movement. Playing on the "continents are complicated" idea, it's entirely possible for continents to split apart, just as they can push together or move around. This is why the Atlantic Ocean is getting larger, and why the African continent will soon split in two.
Many of these forces are complex, and you don't have to consider them all. Consider one of the most commonly suggested supercontinents, and play with it:
| Pangaea Ultima | Amasia | Novopangaea | 208