The transitional period known as the occurred when europe became climatically, geographically, and biologically much as it is today.

Mesolithic era

Explanation:

The Mesolithic era refers to the middle stage of the stone age i.e. between the Paleolithic and Neolithic. The Paleolithic refers to the old stone age and the Neolithic refers to the new stone age. During this time, the microlithic tools and other attacking weapons were made by the early humans, and also there occurred changes in their way of settlement as the climate and geography changed significantly.

The Mesolithic era started about 8000 years to 2700 years back in the past, in the northwestern part of Europe.

Thus, the Mesolithic era occurred when Europe occupied the present landscape, in terms of climate, biology, and geography.