Six Mass Extinctions in Earth’s History. Are We on the Brink of a Seventh?
Scientists define a mass extinction as the extinction of about three-quarters of all species over a short geological period of time, which is less than 2.8 million years, according to The Conversation. Right now, humans are at the beginning of the last mass extinction, which is moving much faster than any other. Since 1970, vertebrate species populations have declined by an average of 68%, and more than 35,000 species are currently considered threatened with extinction, according to the International Union for Conservation of Nature (IUCN). During the 20th century alone, about 543 species of land vertebrates became extinct, according to a research paper in the journal PNAS.
Ediacaran animals are still considered the earliest multicellular animals on Earth
And paleontologists and geneticists are finding more and more evidence to support this fact. Using fossils and genetic dating, scientists have put forward very different candidates for the role of the world’s first animal. Today, animals of all shapes and sizes roam the Earth, from nearly microscopic creatures like tardigrades to 80-foot (25-meter) blue whales. These organisms emerged and developed over millions of years of evolution. But which animal was the first on the planet?