Estimate the average surface temperature of the earth when the sun was 40% dimmer, 4 billion years ago. your estimate does not include the effects of the greenhouse gases (carbon dioxide and water vapor). use a = 0.3 for the earth’s albedo. assuming that the actual temperature of our planet was the same in the past as it is today, compare the strength of the greenhouse effect today vs. its value 4 gy ago. how different would the earth’s atmosphere have been so as to achieve that level of dt?