Permafrost by permafrost. Of this area slightly more than half is underlain by continuous permafrost, around 20 percent by discontinuous permafrost, and a little less than 30 percent by sporadic permafrost. Most of this area is found in Siberia, northern Canada, Alaska and Greenland. Beneath the active layer annual temperature swings of permafrost become smaller with depth. The deepest depth of permafrost occurs where geothermal heat maintains a temperature above freezing. Above that bottom limit there may be permafrost, whose temperature doesn't change annually—"isothermal permafrost". Permafrost typically forms in any climate where the mean annual air temperature is less than the
Merlin diamond mine Merlin diamond mine The Merlin diamond mine is one of only three diamond mines in Australia. The mine is located in the Northern Territory of Australia, about 80 kilometres south of Borroloola. The mine operated for a period of about four years from 2000 to mid-2003, during which time it produced about 500,000 carats (100 kg) of high quality diamonds. The Merlin mine has an unusually high proportion of gem-quality diamonds: 65% of production is gem-quality, and only 35% is classified as near-gem or industrial quality. This compares to a worldwide average of just 20% gem-quality diamond production at diamond