Mystery of the Late Devonian extinction
Between about 385 and 359 million years ago, life on earth was under attack, and 70 to 80 percent of the species on the planet disappeared. However, evidence defining the cause of this catastrophe is sparse. Also, controversy exists over whether there was one event or many events leading to extinction and how long it took. Some researchers propose multiple events over about 20 million years. The answer is uncertain, but there are some clues to the mystery of the Late Devonian extinction.
The Late Devonian is divided into two stages: the Frasnian followed by the Famennian. Paleontologists point to three periods in the Late Devonian where major changes occur in the fossil records: the beginning and end of the Frasnian and the end of the Famennian. Large numbers of species disappeared from the geological records at these points in time
Black Shales
Black shales provide one piece of evidence about Devonian environmental conditions. Layers of black shales deposited at the end of the Frasnian and the end of the Famennian provide a clue. The significance of these shales is that they provide evidence of widespread anoxia (lack of oxygen) in the late Devonian seas. Without oxygen, both fish and bottom-dwelling creatures perished.
