Genesis 1:14-19 “And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years: And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so. And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: he made the stars also. And God set them in the firmament of the heaven to give light upon the earth, And to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good. And the evening and the morning were the fourth day.”
This is my favorite part of the creation story. Just imagine being on the Earth’s surface looking into the sky during the Archean Eon. At that time, the atmosphere was a product of volcanism and outgassing from meteoric impacts and made of hydrogen, methane, water vapor (clouds), and carbon dioxide. There was no day or night, just a perpetual twilight that varied in intensity throughout the day.
As the free hydrogen escaped into space reducing the atmospheric pressure, water vapor condensed and fell out as rain. This formed acidic oceans, rivers and lakes. Shortly thereafter, God created life in the oceans. It existed deep in the water because the UV radiation was so intense life couldn't exist in shallow water. It was also in these depths where the minerals existed which they needed to survive.
Over time, carbon dioxide dissolved into the oceans and these single-cell organisms converted it to oxygen. It then combined with minerals in the water and then the crust, taking more gas out of the atmosphere. In fact, the great majority of Earth's oxygen is sequestered in its crust. Once the minerals were “saturated,” the atmosphere’s oxygen content began to rise. At first, it combined with methane, turning it into carbon dioxide. This allowed more atmospheric cooling since CO2 is not as good an insulator as methane. The rest gathered in the air, soon UV radiation turned some into ozone which accumulated high in the atmosphere. The ozone blocked the harsh UV radiation harmful to life which allowed it to move up from the ocean depths to the surface and eventually onto land.
As the atmosphere thinned, it became more transparent, revealing in order the Sun, then the Moon and then at night, the stars. They had always been there, they were just hidden by the clouds and obscured by the haze. Seen from space, the Earth changed from a world covered completely in clouds to one with partly cloudy skies, brilliant blue oceans, and brown land masses. The perpetual twilight also gave way to the discrete days and nights we are accustomed to.
By the end of the Proterozoic Eon, the Earth with its now transparent atmosphere, an ozone layer to stop the lethal UV radiation, and plenty of free oxygen, was ready for God's next phase: life on land.
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