Continents

[westt]

How did they choose which land masses were the continents? Why is Greenland NOT a continent?

[bernardo]

It's purely a matter of size, and the distinction is arbitrary. Greenland is the largest island, and Australia is the smallest continent. There is no specific geological definition to account for it; e.g. Madagascar is on a different plate from Africa, but it is too small to be regarded as a continent on its own.

[ozguy]

I have been searching for an answer to the 'continent' question for years, and I now believe the answer is very arbitrary and un-scientific.
Generally, a continent must have its own continental shelf surrounding it. (I don't know it Greenland has this).
So, depending on who you ask, there are 4, 5, 6 or 7 continents on Earth.