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Solar activity has been a main driver of climate change over geologic time, although its role in the recent warming has not been found to be significant.〔Hegerl, ''et al.'', (Chapter 9: Understanding and Attributing Climate Change ), (Executive Summary ), in .〕 == Geologic time == Earth formed around 4.54 billion years ago〔 〕 by accretion from the solar nebula. Volcanic outgassing probably created the primordial atmosphere, but it contained almost no oxygen and would have been toxic to humans and most modern life. Much of the Earth was molten because of frequent collisions with other bodies which led to extreme volcanism. Over time, the planet cooled and formed a solid crust, allowing liquid water to exist on the surface. Three to four billion years ago the Sun emitted only 70% of its current power.〔(The Sun's evolution )〕 Under those atmospheric composition, liquid water could not have existed. Over the following approximately 4 billion years, the Sun's energy output increased and atmospheric composition changed. The Great Oxygenation Event around 2.4 billion years ago was the most notable alteration. Over the next five billion years the Sun's ultimate death as it becomes a red giant and then a White dwarf will have large effects on climate, with the red giant phase likely ending any life on Earth. Evidence suggests water's presence, in the Hadean and Archean〔 eons, leading to what is known as the faint young Sun paradox. Hypothesized solutions to this paradox include a vastly different atmosphere, with much higher concentrations of greenhouse gases than currently exist. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Solar activity and climate」の詳細全文を読む スポンサード リンク
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