The Sixth Extinction

 A mass Extinction is:  - When at least half of all species (including animals and plants) die within a relatively short time.  We know these extinction occurred  -Through the fossil record  -Fossils of plants and animals in early layers are suddenly not present in later rock layers.  Scientist believe that 99% of all plant and animal species that have ever lived are now extinct.

 Ordovician-Silurian  440 million years ago  Caused by: sudden global cooling  Extinction of marine organisms  This was a time when the Earth was covered with land plants.

 Devonian Extinction  370 million years ago  Caused by: possible climate change  Extinction of tropical marine species

 Permian – Triassic Extinction  245 million years ago  Caused by: climate change, plate tectonic movement or possible comet or meteor impact.  Largest mass extinction – so far  Killed a range of species, including vertebrates  Only 10% of species survived.

 Triassic – Jurassic Extinction  210 mya  Unknown cause  Extinction of land vertebrates

 Cretaceous-Tertiary  65 million years ago  Caused by: collision of comet or meteor and/or volcanic eruption  Extinction of dinosaurs, marine life, and many other plant and animal species  50 – 75% of animals extinct  Global temperature decreased  Rise of the primates

 The sixth extinction is happening today.  All other mass extinctions were caused by natural disasters.  The sixth, however is being caused by modern humans.

 When modern homo sapiens began to radiate to different parts of the world.  Only in places where early hominids lived (Africa, Europe and Asia) did native plant and animal species survive in the beginning.  Some paleoanthropologists believe that the Neanderthals became extinct due to warfare or competition from modern humans.

North America – 12,500 years ago  - butchering killed off mammoths, mastodons, and ancient buffalos Caribbean – 8000 years ago - Lost all larger native species Madagascar – 2000 years ago -lost larger lemurs elephant birds, a species of hippo, etc.

 1. Pollution  2. Warfare  3. Exploitation of Species  4. Overpopulation  5. Unnatural rates of consumption