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This timeline of natural history summarizes significant geological and biological events from the formation of the Earth to the rise of modern humans. Times are listed in millions of years, or megaanni (Ma). ==The earliest Solar System== In the earliest solar system history, the Sun, the planetesimals and the jovian planets were formed. The inner solar system aggregated more slowly than the outer, so the terrestrial planets were not yet formed, including Earth and Moon. *c. 4,570 Ma: A supernova explosion (known as the primal supernova) seeds our galactic neighborhood with heavy elements that will be incorporated into the Earth, and results in a shock wave in a dense region of the Milky Way galaxy. The Ca-Al-rich inclusions, which formed 2 million years before the chondrules,〔Amelin,Yuri, Alexander N. Krot, Ian D. Hutcheon, & Alexander A. Ulyanov (Sept 2002), "Lead Isotopic Ages of Chondrules and Calcium-Aluminum-Rich Inclusions" (Science, 6 September 2002: Vol. 297. no. 5587, pp. 1678 - 1683)〕 are a key signature of a supernova explosion. *4,567±3 Ma: Rapid collapse of hydrogen molecular cloud, forming a third-generation Population I star, the Sun, in a region of the Galactic Habitable Zone (GHZ), about 25,000 light years from the center of the Milky Way Galaxy.〔According to (isotopicAges ), the Ca-Al-I's (= Ca-Al-rich inclusions) here formed in a proplyd (= protoplanetary disk]).〕 *4,566±2 Ma: A protoplanetary disc (from which Earth eventually forms) emerges around the young Sun, which is in its T Tauri stage. *4,560–4,550 Ma: Proto-Earth forms at the outer (cooler) edge of the habitable zone of the Solar System. At this stage the solar constant of the Sun was only about 73% of its current value, but liquid water may have existed on the surface of the Proto-Earth, probably due to the greenhouse warming of high levels of methane and carbon dioxide present in the atmosphere. Early bombardment phase begins: because the solar neighbourhood is rife with large planetoids and debris, Earth experiences a number of giant impacts that help to increase its overall size. 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「Timeline of natural history」の詳細全文を読む スポンサード リンク
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