The correct answer of the given question above would be option D. The option that did not occur during the Cenozoic era is the formation of the ozone layer. The ozone layer has long been there before any era since it is part of the earth's atmosphere. Hope this answer helps.
Explanation: The formation of the ozone layer did not occurred during the Cenozoic era. It took place 2 million years ago. The formation of ozone layer took many years ago that still is present.
The ozone layer acts as a barrier and provides protection against the harmful radiation. The Cenozoic era started about 65 million years ago which proves the formation of ozone layer took long time ago and not during Cenozoic era.
