On the outskirts of Stockholm, there is an ancient oak tree that has been used to measure changes in sea level. During the last Ice Age, a layer of ice more than three kilometers thick covered the Nordic countries and Canada. All of this mass compressed the earths mantle, lowering the land by several meters. After the ice melted, the mantle started to puff back up slowly—very very slowly. Only by about half a centimeter a year, a negligible amount, but very noticeable over the course of a decades. Today,…
