The Young Earth part 4

Helium Saturation
We use helium to make balloons float in the air, and to make blimps fly. Why? Because it is extremely light. In fact, it is so light that it is all floating into the outer reaches of our atmosphere. If the earth is billions of years old, our atmosphere should be thick with helium. One source of this helium is the decay of uranium, we can measure the helium produced by the decay of uranium, and figure out how much helium is lost into space and come up with a fairly close estimate of the amount of time it would take for the present amount of helium to accumulate in our atmosphere. According to experts, the earth’s age could not be more than 15,000 years by this dating method.

Ref: Unlocking the Mysteries of Creation (p. 57)