Read this and answer the question. If the question is unanswerable, say "unanswerable".

Around 1200 BC, the Dorians, another Greek-speaking people, followed from Epirus. Traditionally, historians have believed that the Dorian invasion caused the collapse of the Mycenaean civilization, but it is likely the main attack was made by seafaring raiders (sea peoples) who sailed into the eastern Mediterranean around 1180 BC. The Dorian invasion was followed by a poorly attested period of migrations, appropriately called the Greek Dark Ages, but by 800 BC the landscape of Archaic and Classical Greece was discernible.

What areas were being explored by others in by sea faring vessels and when are they believed to have left?
unanswerable