What transitional period occurred just before Europe became climatically, geographically, and biologically much as it is today?

Mesolithic Era

Explanation:

The Climate, geographical condition, and biological diversity in The Mesolithic era is drastically different from the current condition because the era was formed shortly after the Last Glacial Maximum.

Before last glacial maximum, the environment surrounding Europe is still covered in ice sheets. After the last glacial maximum period. the temperature in this territory started to rise. Causing a change in climate, land forms, and the type of organisms that can survive.