Short answers, pulled from the story.
The bedrock beneath Gettlinge dates to at least 600 million years ago and consists primarily of Ordovician limestone. Glacial grinding during the last ice age created nearly flat alvar formations from this stone before uplift formed the island of Öland.
Settlements developed on a narrow low-lying ridge running north and south parallel to the Baltic coast. This ridge provided the only place with soil extending more than two centimeters in depth along the southwestern coast of Stora Alvaret World Heritage Site.
Archaeological excavations conducted over years in the latter 1900s revealed bone spears, elk antler harpoons and flint tools. These findings elucidate Mesolithic hunting technologies alongside remains of bear, marten, seal and porpoise.
A wide variety of wildflowers bloom from May to July including stonecrop and dropwort while Artemisia Oelandica is endemic to Öland. Common spotted orchid grows there too alongside Kidney vetch which appears on the limestone pavement ecosystem.
The thicker soil layer provided the only hospitable place for building foundations, burial grounds and agriculture where most other areas had thin soil mantles. Wave action during post-Ice Age uplift formed this specific layer allowing settlements to develop before the glacial cap fully melted.