Simplify the following text for a Grade 6 native English-speaking person.
Original: Glaciologically , ice age implies the presence of extensive ice sheets in the northern and southern hemispheres ; by this definition we are still in the ice age that began at the start of the Pleistocene ( because the Greenland and Antarctic ice sheets still exist ) .
Simplified: We are still , in a sense , in an ice age , because the Greenland and Antarctic ice sheets still exist .