- Doggerland (Wikipedia)
Doggerland was a large area of land in Northern Europe, now submerged beneath the southern North Sea. This region was repeatedly exposed at various times during the Pleistocene epoch due to the lowering of sea levels during glacial periods. However, the term “Doggerland” is generally specifically used for this region during the Late Pleistocene and Early Holocene. During the early Holocene following the glacial retreat at the end of the Last Glacial Period, the exposed land area of Doggerland stretched across the region between what is now the east coast of Great Britain, the Netherlands, north-west Germany, and the Danish peninsula of Jutland. Between 10,000 and 7,000 years ago, Doggerland was inundated by rising sea levels, disintegrating initially into a series of low-lying islands before submerging completely. The impact of the tsunami generated by the Storegga underwater landslide c. 8,200 years ago on Doggerland is controversial. The flooded land is known as the Dogger Littoral.
- Regular tetrahedron (Wikipedia)
A regular tetrahedron is a tetrahedron in which all four faces are equilateral triangles. In other words, all of its faces are the same size and shape (congruent) and all edges are the same length. A convex polyhedron in which all of its faces are equilateral triangles is the deltahedron. There are eight convex deltahedra, one of which is the regular tetrahedron.
