The paleozoic–mesozoic boundary is a major break in the geologic time scale because

Hello There! ^_^

Your question: The paleozoic–mesozoic boundary is a major break in the geologic time scale because..?

Your  The paleozoic–mesozoic boundary is a major break in the geologic time scale because it is when mammals first appeared!

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The answer would be :  mammals first appeared.

Hope this helps !

Photon

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