Between 4 billion and 2.5 billion years ago, the continental shield rock began to form. Approximately 70 percent of continental landmass was formed during this time. Small “island” land masses floated in the molten “seas.” Earth had acquired enough mass to hold a reducing atmosphere composed of methane, ammonia and other gases. Water from comets and hydrated minerals condensed in the atmosphere and fell as torrential rain, cooling the planet and filling the first oceans with liquid water.
Exactly when or how it happened is unknown, but microfossils of this time indicate that life began in the oceans about 3.5 billion to 2.8 billion years ago. It is probable that these microscopic prokaryotes began as chemoautotrophs, anaerobic bacteria able to obtain carbon from carbon dioxide (CO2). By the end of the Archean, the ocean floor was covered in a living mat of bacterial life.
Exactly when or how it happened is unknown, but microfossils of this time indicate that life began in the oceans about 3.5 billion to 2.8 billion years ago. It is probable that these microscopic prokaryotes began as chemoautotrophs, anaerobic bacteria able to obtain carbon from carbon dioxide (CO2). By the end of the Archean, the ocean floor was covered in a living mat of bacterial life.
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