In an article entitled, "Ancient Europeans Mysteriously Vanished 4,500 Years Ago," the author makes the case that the DNA from Europeans changed about 2500 BCE.
Originally, the DNA pointed to settlers from Turkey reaching Germany about 5500 BCE. Further DNA analysis on later burials indicates that another people were present and the older people were no longer around.
The new folks came from the Iberian peninsula, according to the article...
Where did these folks come from before they arrived in Spain or Portugal?
Were they a small population from the fabled Atlantis that finally grew to sufficient size to be able to spread out over Europe?
Or were they connected with the original inhabitants of the American continent that migrated across the Atlantic?
More research and analysis will hopefully answer these questions.
Have a great day.