ammonia’s candidacy led to consideration of other heat-trapping gases. In the 1980s, a team headed by geochemist James Kasting proposed the less potent greenhouse gas, carbon dioxide, as the resolution to the paradox. Kasting’s team calculated that for life to survive on Earth 3.8 billion years ago, the primordial atmosphere must have contained from 100 to 1,000 times as much carbon dioxide as it does today.[4] To answer the question of where so much carbon dioxide came from, the team suggested