Greenland used to have warm temperatures, but when this part of the crust moved to the geographic north pole, this landmass cooled down and an ice cap formed there.
The fact that there still is an ice cap on Greenland is because of this. With the crust moving further, the location of the ice moved to the sea again, which is a location where an ice cap can not be permanent anymore.
Because of all this, there are the remnants of a large ice cap on Greenland, that is still melting. And things are found below the ice from the period that Greenland did have a relatively warm climate.