Heavy Comets

Watched NOVA last night,and found out the Earth got its heavy water
from comets. Heavy water having a neutron in its nucleus. Our oceans
have a great amount of heavy water. Man makes much use of heavy
water. What use does nature have of it.? Is heavy water easy to separate
from regular water since its over twice as heavy? Just let water
stand,and heavy water will go to the bottom????? Is
heavy water to be found locked under Mars surface? Does heavy water
resist the inferred rays of the Sun better than regular water,or vice a
verse. In the beginning was all water heavy,and decayed into more stable
regular water ? Woke up this morning with no theories just questions to
ponder Bert