The latest research into material evidence from the Viking site at L’Anse aux Meadows on the northern tip of Newfoundland has given a precise date for the presence there of Scandinavian colonists, and probably of their first arrival. With a precision that is also historically very tidy indeed the date was 1021, exactly a millennium ago.
The dating is based on evidence from tree rings and relates to a specific event - the effect of solar flares in 992 twenty nine years earlier which can be vouched for in written evidence. Once that indicator is picked up in the timber it is easy to calculate the date timber was felled.
The research work is described in articles from Life Science at Ancient Solar Storm Reveals Vikings Were In North America Exactly 1,000 Years Ago, from Heritage Daily at Study identifies date of Norse settlement in the Americas and from Science at first-viking-settlement-north-america-dated-exactly-1000-years-ago
The BBC News site also has an account at Vikings settled in North America in 1021AD, study says