Archaeological and paleontological evidence proves that we've been using hammerstones for a very long time. The oldest stone flakes were made by African hominins 3.3 million years ago, and by 2.7 mya (at least), we were using those flakes to butcher animal carcasses (and probably wood-working as well).

What time period was the hammerstone used in?

The soft hammer appeared during the Lower Paleolithic, specifically in the Acheulean (it is very visible in certain bifaces), 700,000 years ago in Africa and half a million years ago in Eurasia.

When were stone tools first used?

The earliest stone toolmaking developed by at least 2.6 million years ago. The Early Stone Age began with the most basic stone implements made by early humans. These Oldowan toolkits include hammerstones, stone cores, and sharp stone flakes.