Amber is natures 'time capsule' originating as sticky resin exuded by ancient trees on which insects and other debris became stuck. The resin would continue to run out of the tree and the trapped insects could become completely enclosed, sealing them from the air and thus preventing decomposition - the specimens are frequently perfectly preserved.
Over time the trees died and eventually the resins hardened into amber. In several areas of the world amber is readily available and is dug up for a variety of purposes including making jewellery, but occasionally especially interesting specimens are found which carry huge scientific interest.
The authors of the paper name this fungus Aspergillus collembolorum, presumably because it did not closely resemble a modern species. It is suggested that this fungus was parasitising this insect rather than using it as food once the insect had died as it is the only identifiable fungus on the insect - other examples in amber clearly show several species of fungus attacking individual insects, much as they would today if the insect had already died.
Eocene period ('New dawn') of the fossil record, a time when the first mammals were emerging and the world experienced a period of high temperatures and warm oceans. Several continents that are today quite separate were joined at the beginning of this period - Australia and Antarctica were linked, Europe, Greenland and North America where just starting to drift apart.