Wait, which evidence is that and where did you read this? Nearly all archaeological studies in Iceland have been carried out by Icelandic archaeologists exclusively and the general consensus among them is not in favor of settlement in Iceland before ~870. I am Icelandic, have studied both history and a bit of archaeology at the University of Iceland and have read archaeological reports on this matter in Icelandic.
I certainly don't have your credentials and I don't really believe in being tightly conservative with my opinions. Before I begin, I want to make it clearer on what I was talking about. Large scale settlements, starting with Ingólfur Arnarson, begin what I would consider the start of organized settlement in Iceland. But, before that, we have:
1. Dicuil, Irish monk and geographer. His "
De mensura Orbis terrae" is a geographical work that mentions a place called "Thule" in the north. While Thule has been used to describe any number of places beyond the known borders of the world, I strongly suspect Dicuil's Thule was truly Iceland. The Faroe Islands were already settled by his time and I don't believe his expedition stopped at only at the Faroes. The Faroes were clearly not "Thule" in his mind, not with what knowledge he had of the islands. An assumption. I do a lot of that.
2. Kverkarhellir Cave would be the location of those crosses you mention. Radiocarbon dating gives the small, probably monastic settlement, a vague guess of "around 800". It could be much later or much earlier than that. I've read about more radiocarbon dates being pushed back rather than pushed forward, so another assumption for sure, but not a completely blind one. Not that much of a stretch to think that monks living on the Faroes traveled further north, probably with or after other small groups.
3. Recent digs at Hafnir give a date anywhere from 770 to 870 for what was a singular cabin. Another wide margin of error in time but between even between what was lost to the ages and what was built over, we can make some well founded assumptions.
Iceland was known to some people in the south. Those living in the Faroes surely must have known about another, larger island to the north. Probably known to some in Ireland and Scotland as well. I don't see why there couldn't be small scale, singular attempts to settle the island. Not a true settling like the Norse did in the 800's but something more sporadic, often temporary. I expect that further digs in Iceland would slowly start to add more and more evidence for earlier, smaller, attempts to live there.
