02 Music of the Celestial Spheres / The Primordial Ocean

Between 4.4 and 4.0 billion years ago*, the Earth cooled, and water vapor in the atmosphere condensed into torrential rains, forming the first oceans. The presence of liquid water, capable of dissolving and carrying a wide range of elements, became the foundation for the chemical reactions that would one day give rise to life. These oceans were nothing like those of today: oxygen was nearly absent, while iron and sulfur were abundant, creating a strongly reducing environment. The Moon, about 20% closer to Earth than it is now, exerted tidal forces that were nearly twice as strong as those of the present day. *Regarding the Late Heavy Bombardment, a leading theory holds that giant impacts capable of vaporizing entire oceans had ceased by 4.2 billion years ago, while smaller meteorite bombardments had ended by around 3.9 billion years ago. Zircon minerals discovered in Western Australia indicate that both land and oceans already existed by 4.4 billion years ago. Meanwhile, the Acasta gneiss found in northwestern Canada shows that continental crust was present as early as 4.0 billion years ago. 03 天体の音楽／太古の海 ４４〜４０億年前に*は地球が冷え、大気中の水蒸気が凝縮して大量の雨が降り、海が形成された。様々な元素を溶かし込むことが出来る液体の水が存在可能になったことは、生命誕生のための化学反応を進める基礎となった。現在とは全く異なり、海中の酸素はほぼゼロ、鉄や硫黄が豊富で還元的、月は今よりも２割ほど地球に近く、潮汐力は2倍くらい強かったらしい。 *後期銃爆撃期については、全海洋を蒸発させるような巨大隕石の衝突は42億年前に、小規模な隕石は39億年前には終わったという説が有力だ。西オーストラリアで発見されたジルコン鉱物は44億年前には既に陸と海が存在していたことを、カナダ北西で発見されたアカスタ片麻岩は40億年前には大陸地殻の存在していたことを示している。