Mass Extinctions

hello there I may look strange to you but I like to be prepared at all times for whenever the next mass extinction might happen but I do think it's important to impart this information in a non muffled way so I think I'm just gonna oh that sucked I have to wear that all the time so you never know when the next mass extinction is going to happen I mean there have been five of them in the last 450 million years alone and it's not like a mass extinction of some kind of blurry ill-defined term it's when at least 50 percent of the species on the planet go extinct one of them which has been aptly dubbed the Great dying wiped out more than 95 percent of the species on the planet it's enough to make you walk around with a gas mask Boswell's of the gas masks is excessive it's also possible that it's useless I mean if we get hit by a big meteor probably not going to help that much mass extinction events happen pretty fast in a geological scale but the actual like dying occurs on our scale quite slowly tens of thousands of years and of course the most important thing to look at here is what these five giant mass extinction events had in common so that we can see them coming climate change usually caused by changing co2 levels and relatively rapid global temperature changes yes you see where I'm going with this I don't mean to alarm anyone here but the idea that the earth is currently as I sit here going through a sixth mass extinction event is actually not that crazy scientifically it actually might make really good sense before we even look at climate change we already know that humans have been a strange and mysterious and new force for mass extinction current extinction rates are somewhere between 100 and a thousand times what they would be naturally due to humanity's very enterprising nature and that rate is similar to or even greater than the rates of some mass extinction events of the past so let's forget about all that depressing stuff for a moment and hop into this scishow Time Machine our first stop 450 million years in the past and we're gonna give little bit wet because pretty much all life on earth at that time was in the ocean welcome everyone to the Ordovician Silurian mass extinction event now you're not going to see any giant comets meteors falling from the sky but sometime in the next 10 million years or so we're gonna see two really dramatic die offs both of them involving the influx of gigantic glaciers and dramatic worldwide falls in sea level these two events will be separated by about 1 million years now it's geologic time remember people and by the end of the second one 27% of honoring families and 60% of all Marine general were extinct and I can tell from your blank stares that we're going to require a little bit of a refresher on the biological classification system which of course classifies all life based on common descent and which we will be talking a lot about as we get more into extinction event starting with the most specific and then getting to the most general we have species genus family order class phylum kingdom domain and good old life back to the Ordovician event what scientists think happened here was that Gondwana one of the two super continents at the time moved into the polar region this set off a huge drop in temperature also a huge increase in glacial formation which dropped sea level marine invertebrates were the hardest hit two-thirds of all the brachiopod and bryozoans families disappeared was also a tough time to be a bivalve or a trilobite and it's because I find this fascinating there's also another theory about what may have happened to cause the Ordovician event a gamma-ray burst from a hypernova somewhere within 6,000 light-years of Earth a supernova that's when a star explodes a hypernova is when a star that's like 100 to 300 times the size of the Sun explodes even like 10 seconds of a gamma-ray burst from a hypernova would completely destroy the ozone layer and dose everything on earth with a nice healthy amount of UV radiation when I say healthy I mean unhealthy all right everybody back in the time machine we're going ahead a hundred million years to 360 million years ago through the late devonian extinction this is the beginning of a prolonged series of mass extinctions in which half of all Jenner and 70 percent of all species will go bye-bye marine life will once again be hit very hard but so will the spiders and the scorpions and the proto and Vivienne's which are just taking their first steps out on the land narrowing down a time frame for this event has been difficult scientists can only say that over a period of five hundred thousand to twenty five million years that's a big gap there I know there were a series of extinction pulses each lasting about a hundred thousand years no gamma-ray bursts are suspected here this is once again being caused by a global drop-off and temperatures people aren't sure what caused it probably either an asteroid impact or a giant supervolcano each of those things would have released massive amounts of dust or ash into the atmosphere drastically changing the climate glaciers probably once again inundated Gondwana what we also know is that ocean levels fell and lost most of their oxygen in the process and what's called ocean anoxia some believe that temperatures in the steaming seas of the Devonian fell from 93 to about 78 degrees coral reefs were hit so hard that it would be a hundred million years before they recovered but there's another interesting theory here and that's that plants which were for the first time really taking hold on land were absorbing so much carbon dioxide from the atmosphere that they actually caused global cooling so in fact plants were responsible for that mass extinction event how could you and now we will travel to the big one also known as the Permian Triassic extinction event also known as the Great dying it is now about 250 million years ago in a combination of catastrophic events is about totally alter life on planet Earth so destructive is this event that it remains the only known mass extinction of insects this may have been triggered by a comet or asteroid impact but what scientists feel fairly certain about is that a subsequent volcanic eruption in an area known as the Siberian traps was responsible for an increase in global temperatures of five to ten degrees these volcanic eruptions covered an area roughly the size of Western Europe and they lasted for a million years but then it got worse the sudden release of gases from methane hydrate reservoirs below the sea floor possibly caused by underwater volcanic activity decimated the seas leading to periods of too much oxygen called hyperoxia and too little oxygen the return of anoxia and marine life does not fare well in either of these conditions these two events at least possibly others led to a shift in ocean currents and general inhospitable environment for most the earth species when the die-off was finally finished 53% of marine families 84 percent of Marine general 70 percent of land species and 95 percent of marine species were extinct the Permian extinction had an enormous evolutionary effect taking place just as mammal-like reptiles like pellicer sores and therapsids were in their prime it would be more than 30 million years before these vertebrates and the earth in general would recover but it did recover until 200 million years ago when the triassic-jurassic extinction killed off many early land animals this includes the death of most of the therapsids large amphibians and the arcus ores paving away for the age of the dinosaurs sign is probably no less about this mass extinction event than any other but what is known is that 23 percent of families and 48 percent of general went extinct but what was left fairly untouched were plants and dinosaurs which now had a lot less competition this was roughly the time when the massive supercontinent known as Pangaea was breaking apart due to volcanic eruptions and the massive release of carbon dioxide from those eruptions may have caused some pretty intense global warming again species don't fare well when temperatures increased quickly like this and it wouldn't be an extinction event without scientists wondering about whether or not there was a massive impact of some kind but so far nobody's found any likely crater candidates do you know where there is evidence of an impact crater right off the coast of Mexico's Yucatan Peninsula and you've heard of this one it's where a giant asteroid or comet struck about 65 million years ago and that kicked off the Cretaceous tertiary extinction you know this one it's the one that killed off all the non-avian dinosaurs and ushered in the glorious age of mammals and birds that wasn't Birds the KT extinction as it's also known killed off half of all general and 75% of species and while the giant asteroid impact winter theory is the leading one it's by no means the only woman also happening at the same time there was a giant volcanic eruption in India that may have caused massive global warming and that final extinction event brings us back around to today where 99% of the species that have ever existed on this plane are extinct but we aren't we are the 1% not lucky for us in the history of humanity we haven't had to deal with any giant comet strikes or super volcanoes but we do have deal with a possibly equally destructive force each other some scientists think that we are already in the middle of an event that's moving faster than the KT extinction but instead of being driven by continents or volcanic eruptions these extinctions are being caused by a rising co2 levels habitat destruction invasive species pollution and over harvesting we already know what changes in global temperature can do to a planet click over here for information on on that in our climate change video a normal extinction rate for our planet is about 10 to 25 species per year and we're already doing about a hundred times that so clearly the 7 billion of us here on this planet are having a pretty big impact I guess the question that remains for us to answer is what are we going to call this sixth mass extinction event and I would love for you to leave ideas for that in the comments thank you for watching of course their sources for all of our information down in the description because we are scientists they are we we do hard to breathe we are round if you have questions or suggestions on Facebook Twitter and of course in the YouTube comments below and if you want to continue to be smarter and know more about the world go to youtube.com slash slash now and subscribe goodbye

Channel: SciShow

Views: 1,000,072

Rating: 4.8969674 out of 5

Keywords: extinction, mass extinction, scishow, science, biology, climate change, species, great dying, geological time scale, co2, temperature change, extinction rate, time machine, ordovician-silurian, die-off, glacier, glacial, gondwana, pangea, gamma ray burst, hypernova, ozone layer, extinction pulse, asteroid impact, supervolcano, late devonian extinctions, permian-triassic, dinosaur, cretaceous-tertiary, k-t, human impact

Id: FlUes_NPa6M

Length: 10min 26sec (626 seconds)

Published: Mon May 21 2012