An impact site may also be surrounded by an ejector blanket. This is a layer of material thrown out by the formation of a crater. For example, the Ries crater in southern Germany is surrounded by a blanket of material up to 100 metres thick. More direct evidence is to find traces of the object that made the crater, such as nickel or iron deposits. A slightly more contentious clue to a cosmic impact is the presence of tektites .
Tektites are smooth glass-like stones that are found in certain sedimentary layers on earth.
They range in size from a few centimetres to microscopic. These stones show clear signs of having been heated twice. The first heating process seems to have reduced the entire rock to a molten state, while the second only seems to have effected the outer layers. Some tektites are teardrop shape, indicating that they have been moulded by aerodynamic forces. Tektites Tektites are believed to be formed by asteroid and comet impacts.