earth-is-on-the-cusp-of-a-sixth-mass-extinctionEarth may be in the early stages of a sixth mass extinction, an international team of scientists says.Animals and plants are threatened. More than 320 land vertebrates have gone extinct since 1500, the researchers said. The world’s remaining animals with backbones are 25 percent less abundant than in 1500— a trend also seen in invertebrate animals, such as crustaceans, worms and butterflies, the scientists reported.The previous mass extinction, which wiped out the dinosaurs, happened about 65 million years ago, likely from a catastrophic asteroid that collided with Earth. In contrast, the looming sixth mass extinction is linked to human activity, Rodolfo Dirzo, a professor of biology at Stanford University in California, said in a statement. Dirzo is the lead author of the new review of past research on the topic, which suggests Earth is in the early days of this sixth mass extinction. More