Earth ozone started to form some billion years ago. It gradually lead to the formation of the stratosphere.
- Earth ozone stated to form some 600 million year. As a thin layer was formed around the earth's surface capable of protecting life on earth.
- The Paleozoic era marks the formation of ozone gas. As ot was time when the geologic and climatic events took shape.
Hence the option A is correct.
Learn more about the first began to form in the stratosphere during.
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