How much sunlight is blocked by dust from an asteroid impact? When you look at the spherea of a radius R, the area blocked by the sphere (the cross sectional area) is \pi . The amount of sunlight blocked by the dust will depend on the summed cross-sectional area of all the dust particles rather than on their total mass. Assume each dust particle is spherical and has a density of 2 g/cm. Assume that the diameter of the asteroid is 10km, and the volume of the material ejected from the crater is 60 times that of the asteroid. (a) What would be the sum of the cross-sectional areas of all the dust particles lofted to the upper atmosphere from the asteroid and crater (assuming only 20% of all volume is lofted into the upper atmosphere) if each dust particle had a radius of 5x107m and if the radius were 5 x 10 m