Scientists are sounding the alarm that Earth has entered its sixth mass extinction as species die out at 100 times the normal rate.

A vicious cocktail of habitat loss, climate change, pollution, and poaching has resulted in a stunning loss of species since the year 1500: a total of 77 mammals, 140 birds, 34 amphibians, according to a New Zealand Herald report.

Some of those species are famous: everyone knows about the Dodo bird, and many have heard of the Steller’s sea cow, Falkland Islands wolf, and the Caspian tiger. But there are countless other species you haven’t heard of that are silently dying off, and nothing has been done to stop what scientists are terming a mass extinction event that is currently underway.

Stanford University scientists say that this is the biggest loss of animal species since the Cretaceous-Tertiary mass extinction event — the same one that spelled the end of the dinosaurs. That took place 66 million years ago.

If anything, scientists are underestimating mankind’s negative effects on the planet, as many species on Earth are on the verge of extinction, and many of them have absolutely no hope of recovering.

Researchers were able to come to their conclusions by examining the fossil record to determine the “background rate” of extinctions, and then compared it to what would be a conservative estimate of how much extinctions humanity has caused in the last 500 years. They found that species in the wild usually die out at a rate of two species of mammal every 10,000 years mainly because of natural population changes, but the rate seen in the last 500 years has been 114 times that mark.

An alarming one in four mammals today is at risk of extinction, as well a whopping 41 percent of amphibians. Many species are still alive today, but only because they are kept in captivity. It could take millions of years to recover from this extinction event, and it could threaten the human race itself, scientists warn.