another example wolves wolves are the stuff of myths legends fairy tales nightmares wolves always attack the people of those stories there is actually no documented attack by the wolves on a human anywhere in the world but that hasn't stopped the myths or legends wolves are carnivores they are pack hunters they are nocturnal you don't see them too much and their howls at night are very distinctive so maybe that created the mythology they do however eat farm animals cattle sheep they are their prey so ranchers don't like here in the United States we hunted down and shot to death the last native wolf sometime in the first third of the 20th century don't war wolves gone finished it was in Yellowstone National Park they first noticed the problem the wolf had been the apex predator now they were gone the herbivores elk all kinds of deer other critters we're reproducing out of control they were eating all the vegetation the ate all the grass the place was turning brown they ate the bushes no ever animals to hide denuded river banks the river ecosystems were changing they couldn't eat the trees but they sure could eat the baby sapling trees so the old trees were surviving but there were no you know young ones coming on to replace them it was becoming an ecological disaster the park had shooting parties who lived go out and shoot down as many deer as they could but it occurred to somebody that what they needed was a natural ecosystem and so in the early 1990s they went to Canada and bought a dozen wolves Canada haven't exterminated all their ones brought the Wolves into Yellowstone Park he created a fenced off area for put the wolves at that and the Wolves established a den made themselves comfortable and finally when it looked like the wolves were happy where they were they removed the fence or let him roam free it worked the Wolves multiplied when he got they got too many a young enterprising one would set off and found a new pack somewhere else today I think there are about eleven packs of wolves in Yellowstone that may sound like a lot that Yeltsin is gigantic it's in parts of three states now that the Wolves are preying on the large herbivores keeping their numbers under control the park vegetation is coming back to where it should be it's a success story the left and right picture panels on this Yellowstone sign depict the difference the denuded river banks and their versus the red lush vegetation the brown versus the green the swarms of deer the Wolves dealing with them something they stress in Yellowstone is the enormous difference it's made to the health of their rivers but now spreading further there are no fences of the boundary of the National Park outside the National Park you come to ranch that the ranchers are not happy up in the states surrounding Ulster Wyoming Montana there are two opposed schools of thought it's more extreme anti-trump there's wolves are vital to our healthy ecosystem and there's the only good wolf is a devil the Endangered Species Act actually had the government paying ranchers for animals that were killed by wolves so they got their money back but they still didn't like but with the Endangered Species Act it was illegal to shoot the corpse you could get arrested and find people did also spread multiplied beyond Yellowstone today there are one or two packs of wolves in the Rocky Mountains in Montana Washington Oregon wolves one or two wolves have even visited the northeast corner of California up on the Klamath Plateau so the government decided they can come off the endangered species list what happened branches declared open season started shooting every wolf they could see within six months they have to go back on the list again grizzly bears grizzly bear is on the state flag of California kind of interesting first they shot and killed the last grizzly bear in California then they put it on the state flag never quite understood that grizzly bears exist in some state parks they are fairly common in Alaska there awfulest reason for that again doesn't have too much to do with the Endangered Species Act it's the change in modern society the rise of ecotourism today grizzly bears are worth more to the economy alive so the tourists will flock in you can have an industry that takes tourists out to observe as grizzly bears they're worth more that way than they are shot stuffed and hung on the wall so the successes the Endangered Species Act are very limited thousands of species remain firmly on the endangered species list and sadly more of them go extinct every year overall how serious is this extinction issue well let's see 65 million years ago a rock several miles in diameter hurtling through space crashed into the earth it hit on what is today a North Shore of the Yucatan theater in Mexico and impact blasted a hole in the ground 160 miles wide and 40 miles deep imagine looking down a hole 40 miles 40 vertical miles into the interior of the earth the energy liberated in that impact produce a foul ball that immediately incinerated about half of the planet all the vaporized and fragmented rock and stuff from both the incoming rock and the 160 by 40 mile chunk of planet Earth was blasted I want to say blasted into the air whether it went long well before beyond the air into space some of it blasted away from the planet and has become meteors headed for other planets a lot of it held by crafted by gravity stayed around the earth anyhow all that stuff blocked out 100% of the Sun what happened to temperatures fell dramatic well below freezing stave that way for well we don't really know whether it was months or years a long time total darkness freezing temperatures what happens to plants well without light they can't focus emphasize they can't make food they die animals eat plants what happens to animals they die this event is of course famous for the extinction of the dinosaurs and everybody knows about that burn the dinosaurs were the tip of the iceberg about 50% of all species or life-forms on the earth perished in that event either immediately or in the ensuing years it's what we call a mass extinction there have been others there was a mass extinction about 200 million years ago in which about 90% of all the organisms on earth perished the further you go back in time the harder it is to be certain of the exact course the 65 million year then we know exactly what happened we found the crater we can see the hole in the ground there is a layer of debris the stuff from the atmosphere falling back to the earth around the world at this time containing very distinctive features small spherical bits of glassy rock which quite clearly were molten droplets flying through the air solidifying and cooling before they hit the ground angular shattered the fragments of crystals clearly the result of a giant impact and a high concentration of an unusual element called iridium very rare on earth very common in the majority of meteorites you know even before we had the crater putting those together the droplets of molten rock the shattered crystals the extra-terrestrial iridium geologists were like 99% sir this was a giant impact it forms a layer of rock today the rocks below it older than it team was fossils of all kinds of species the rocks above it have a virtually barren and only have a few the fossils of a few surviving species going back further in time it is harder to pin down the exact cause of a mass extinction earth recycles is rocks there's less evidence some geologists think that the 200 million year event was also an extraterrestrial impact but they haven't any proof other geologists say no but they point to a giant outpouring of volcanic lava unprecedented covering much of India in thousands of feet of basaltic lava they say this poison of the atmosphere that's a talent cause some people have put the two together and said a charred impact destabilized the interior of the earth sufficiently to cause this unprecedented outpouring of lava so it's posed together nice idea but again we don't have any proof but yes over the Earth's history there have been five of these mass extinctions with the extinction of the dinosaurs 65 million years then being the last one now over the last century roughly it is estimated that we humanity have caused the extinction of approximately 50 percent of all the life-forms on earth that's the same scale as that giant rock from space the rock from space arrived one dead we've taken 100 years geologically 100 years is like one day it's nothing you might have heard of dressup Sundberg and some of her speeches say we're in the middle of a mass extinction we are you can find a book out there entitled the sixth mass extinction that's on the sign was carried by some of the climate activists protestors the sixth mass extinction five of them produced by Nature the sixth one caused by us one big difference after the space rock had impacted and after the dust settled life gone back to diversifying and repopulating the planet has our damage ceased allowing nature get to get back to repairing the damage absolutely not our damage is continuing its accelerating we're also to be way worse for our biosphere however that space rock was yes it is very serious