Continental crust

However, 94% of the Zealandia continental crust region is submerged beneath the Pacific Ocean,[4] with New Zealand constituting 93% of the above-water portion.

Its existence also provides broad expanses of shallow water known as epeiric seas and continental shelves where complex metazoan life could become established during early Paleozoic time, in what is now called the Cambrian explosion.

The relative contributions of these two processes in creating continental crust are debated, but fractional differentiation is thought to play the dominant role.

Proponents of a steady-state hypothesis argue that the total volume of continental crust has remained more or less the same after early rapid planetary differentiation of Earth and that presently found age distribution is just the result of the processes leading to the formation of cratons (the parts of the crust clustered in cratons being less likely to be reworked by plate tectonics).

[15] In contrast to the persistence of continental crust, the size, shape, and number of continents are constantly changing through geologic time.

The edges of continental fragments formed this way (both sides of the Atlantic Ocean, for example) are termed passive margins.

The high temperatures and pressures at depth, often combined with a long history of complex distortion, cause much of the lower continental crust to be metamorphic – the main exception to this being recent igneous intrusions.

Also, material can be accreted horizontally when volcanic island arcs, seamounts or similar structures collide with the side of the continent as a result of plate tectonic movements.

[14] It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time.