Mass extinctions are defined by the loss of at least 75% of species within a relatively short period of geological time. We are currently in the sixth mass extinction (or Anthropocene extinction) of the Holocene epoch. Vast numbers of species of plants and animals including mammals, birds, amphibians, reptiles and arthropods are dying off in alarming numbers due to widespread destruction of habitat, irresponsible agricultural practices that result in the poisoning of our food and water source, overfishing, and a rise in temperature due to irresponsible burning of fossil fuels. The oceans are getting warmer and more acidic, plastic waste is showing up in our drinking water and shellfish and our air and water quality are being threatened by careless, short-sighted policy. The arrival of humans on different continents coincides with the extinction of large mammals that occurred at the end of the last Ice Age.
A representative from the endangered list from each of the groups that are at risk of extinction - mammals, birds, insects, marine creatures - are represented in the top of the hourglass with little hope of escaping the pull of gravity that has almost consumed the human being. The oroborous represented by a snake chasing its tail symbolizes the cycle of life and death.
The previous five extinctions are featured in the lower part of the hourglass with extinct species indicated in fossil form:
End Ordovician, 444 million years ago
Late Devonian, 375 million years ago
Permian-Triassic Event 251 million years ago
Triassic-Jurassic Extinction Event 200 million years ago
Cretaceous-Paleogene Extinction Event 66 million years ago