All of the continents that are seperate today were in the form of a single giant continent up until approximately 175 million years ago.
They drifted apart in time because of the molten lava that is constantly flowing right underneath the earth's hardened shell. Also, archeological discoveries that indicate the same species of animals/plants lived on different continents such as Europe and America long before humans or intercontinental travel were around.
Barrow Alaska is an example of a polar tundra climate that is marked by low vegetation growth, cold temperatures, low amounts of precipitation, and no true summer.
