Comets, ice ages, and ecological catastrophes

A total mass similar to 10(14) g added to the Earth's upper atmosphere in t he form of small particles of high albedo for visual wavelengths would prod uce an inverse greenhouse effect, shielding ground level from sunlight but permitting infrared radiation from the ground to escape into space. Such a mass of small particles might be acquired by the Earth in a close approach to a cometary nucleus. Ice ages and ecodisasters, such as that which occurr ed 6.5 x 10(7) years ago, could arise from the effects of such an addition of small particles.