Kasting James F, Ono Shuhei
Penn State University, Department of Geosciences, University Park, PA 16802, USA.
Philos Trans R Soc Lond B Biol Sci. 2006 Jun 29;361(1470):917-29. doi: 10.1098/rstb.2006.1839.
Earth's climate during the Archaean remains highly uncertain, as the relevant geologic evidence is sparse and occasionally contradictory. Oxygen isotopes in cherts suggest that between 3.5 and 3.2 Gyr ago (Ga) the Archaean climate was hot (55-85 degrees C); however, the fact that these cherts have experienced only a modest amount of weathering suggests that the climate was temperate, as today. The presence of diamictites in the Pongola Supergroup and the Witwatersrand Basin of South Africa suggests that by 2.9 Ga the climate was glacial. The Late Archaean was relatively warm; then glaciation (possibly of global extent) reappeared in the Early Palaeoproterozoic, around 2.3-2.4 Ga. Fitting these climatic constraints with a model requires high concentrations of atmospheric CO2 or CH4, or both. Solar luminosity was 20-25% lower than today, so elevated greenhouse gas concentrations were needed just to keep the mean surface temperature above freezing. A rise in O2 at approximately 2.4 Ga, and a concomitant decrease in CH4, provides a natural explanation for the Palaeoproterozoic glaciations. The Mid-Archaean glaciations may have been caused by a drawdown in H2 and CH4 caused by the origin of bacterial sulphate reduction. More work is needed to test this latter hypothesis.
太古宙时期地球的气候仍然极不确定，因为相关地质证据稀少且偶尔相互矛盾。燧石中的氧同位素表明，在35亿年至32亿年前，太古宙气候炎热（55 - 85摄氏度）；然而，这些燧石仅经历了适度程度的风化这一事实表明，当时气候如现今一样温和。南非庞戈拉超群和威特沃特斯兰德盆地中杂砾岩的存在表明，到29亿年前气候已处于冰川期。太古宙晚期相对温暖；然后在古元古代早期，约23亿至24亿年前，冰川作用（可能是全球范围的）再次出现。要将这些气候限制条件与一个模型相匹配，需要大气中高浓度的二氧化碳或甲烷，或两者皆有。太阳光度比现今低20% - 25%，因此需要提高温室气体浓度才能使地表平均温度保持在冰点以上。在约24亿年前氧气增加，同时甲烷减少，这为古元古代冰川作用提供了一个自然的解释。太古宙中期的冰川作用可能是由细菌硫酸盐还原作用的起源导致氢气和甲烷减少所引起的。需要开展更多工作来检验后一个假设。
