Scientists studying many different parts of the planet's ecosystems are warning that Earth may be on the verge of a sixth major mass extinction event. In a series of papers published this week in the Proceedings of the National Academy of Sciences, researchers examining biodiversity around the globe paint a gloomy picture for the planet's species. Warning signs include recent mass die-offs of amphibians and declining fisheries.Over the course of the Earth's history, there have been at least five major extinction events -- the End Ordovician, Late Devonian, End Permian, End Triassic, and End Cretaceous. But are we facing a sixth major extinction?
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