They have argued that methane—with many times the heat-trapping capacity of carbon dioxide—may have been more abundant, 他们提出，在当时，甲烷（一种比二氧化碳更有效率的温室气体）的含量可能非常丰富，部份原因是甲烷在缺少氧气的远古大气中，生命期长达一万年的时间。