Carbon dioxide sequestration more than 3.7 billion years ago and the oldest climate cycles. More than 3.7 billion years ago atmospheric greenhouse CO2 was sequestered into limestone sedimentary rocks deposited in ice-free oceans. Why then, with the 30-25 per cent cooler sun in those times, was our earth not frozen over? Solving this oldest climate problem, will give the deepest-time perspective to the earth's changing climate feedback loops.