Archean Atmosphere n Faint young Sun paradox presents

Archean Atmosphere n Faint young Sun paradox presents dilemma u 1) What is the source for high levels of greenhouse gases in Earth’s earliest atmosphere? u 2) How were those gases removed with time? t Models indicate Sun’s strength increased slowly with time t Geologic record strongly suggests Earth maintained a moderate climate throughout Earth history (i. e. , no runaway greenhouse like on Venus)

Source of Greenhouse Gases n Input of CO 2 and other greenhouse gases from volcanic emissions u Most likely cause of high levels in Archean

n n Removal of Atmospheric CO 2 Slow chemical weathering of continental rocks balances input of CO 2 to atmosphere Chemical weathering reactions important u Hydrolysis and Dissolution

Atmospheric CO 2 Balance n Slow silicate rock weathering balances long -term build-up of atmospheric CO 2 u On the 1 -100 million-year time scale u Rate of chemical hydrolysis balance rate of volcanic emissions of CO 2 t Neither rate was constant with time u Earth’s long term habitably requires only that the two are reasonably well balanced

Chemical Weathering: Earth’s Thermostat? n Chemical weathering can provide negative feedback that reduces the intensity of climate warming

Chemical Weathering: Earth’s Thermostat? n Chemical weathering can provide negative feedback that reduces the intensity of climate cooling

Greenhouse vs. Faint Young Sun n Cold surface temperatures created by the faint young Sun compensated by stronger atmospheric CO 2 greenhouse effect

Archean Volcanism & Weathering n n Early Archean volcanism probably produced more atmospheric CO 2 u Counteracted lower radiant energy and warmed our planet u Volcanism did not slow at same rate as Sun increase in strength Young Earth probably still cold u Weathering slow u Continents small u Continental crustal rocks silica-poor (basaltic) t Less efficient CO 2 removal from atmosphere

Greenhouse vs. Faint Young Sun n When solar luminosity strengthen, chemical weathering increased and helped transfer atmospheric CO 2 into sediments