Complex sentence: The Stone Age is a prehistoric period in which stone was widely used in the manufacture of implements lasting roughly 2.5 million years, from the appearance of the genus Homo about 2.6 mya to between 4,500 and 2,000 BCE with the appearance of metalworking.
Split into simpler sentences: The Stone Age is a prehistoric period in which stone was widely used in the manufacture of implements. This period occurred after the appearance of the genus Homo about 2.6 million years ago and roughly lasted 2.5 million years to the period between 4,500 and 2,000 BCE with the appearance of metalworking.