ms. abrahams. nancy, in just a moment. but i want some dark matter. and dark matter are in theory of it was originated in part by you, back in the 80s, correct? when you fought the battle of, is there dark matter? because there is nothing sensory about dark matter. you can't look tat under a microscope, correct? >> right. >> how do you know it exists? >> by the affects on the motions of other objects and also because it bends light. >> you're talking about gravity? >> yes, it has gravity. >> is it a benign gravity? >> well, gravity never sleeps and it can cause terrible destruction. for example near black holes. so gravity certainly is benign for us. it's what is keeping us in our seats. but it can have very bad affects if you happen to slip at the edge of a precipice. >> what did it -- what did dark matter do that was constructive for the evolution of the universe, the evolution of the earth? the earth is about 5 billion years old? >> 4.6 billion years old. >> when did man get here? >> it depends on how you define man. >> hom nids. >> hom nids about