1 00:00:09,980 --> 00:00:13,080 in the beginning there was darkness and 2 00:00:13,080 --> 00:00:16,350 then bang giving birth to an endless 3 00:00:16,350 --> 00:00:18,960 expanding existence of time space and 4 00:00:18,960 --> 00:00:22,439 matter every day new discoveries are 5 00:00:22,439 --> 00:00:24,119 unlocking the mysterious the 6 00:00:24,119 --> 00:00:26,820 mind-blowing the deadly secrets of a 7 00:00:26,820 --> 00:00:30,380 place we call the universe 8 00:00:32,170 --> 00:00:34,550 throughout its more than four billion 9 00:00:34,550 --> 00:00:37,850 years of existence planet Earth has 10 00:00:37,850 --> 00:00:42,070 endured some extremely rough days 11 00:00:42,230 --> 00:00:45,380 the very worst was it a shattering 12 00:00:45,380 --> 00:00:47,660 encounter with a planet that got too 13 00:00:47,660 --> 00:00:49,430 close 14 00:00:49,430 --> 00:00:50,780 and anything been there it definitely 15 00:00:50,780 --> 00:00:53,780 wouldn't have survived or a hot shower 16 00:00:53,780 --> 00:00:56,270 of deadly rays that almost scoured the 17 00:00:56,270 --> 00:01:00,680 planet clean of life the blast from the 18 00:01:00,680 --> 00:01:03,020 impact would have laid waste a thousand 19 00:01:03,020 --> 00:01:04,760 miles in every direction it's literally 20 00:01:04,760 --> 00:01:06,050 the sound heard round the world 21 00:01:06,050 --> 00:01:08,930 for a runaway volcanism that led to vast 22 00:01:08,930 --> 00:01:11,900 extinctions to tiny microbes that 23 00:01:11,900 --> 00:01:15,200 triggered a global deep freeze life has 24 00:01:15,200 --> 00:01:17,150 teetered perilously close to the break 25 00:01:17,150 --> 00:01:20,510 time and time again war life died then 26 00:01:20,510 --> 00:01:23,750 than any time since and maybe any time 27 00:01:23,750 --> 00:01:25,430 before this was the biggest and the 28 00:01:25,430 --> 00:01:26,570 baddest of them all 29 00:01:26,570 --> 00:01:29,630 are the darkest hours behind us or 30 00:01:29,630 --> 00:01:32,640 lurking in the distant future 31 00:01:32,640 --> 00:01:36,150 take cover as we count down the seven 32 00:01:36,150 --> 00:01:40,220 worst days on planet Earth 33 00:01:46,850 --> 00:01:49,910 [Music] 34 00:01:56,290 --> 00:01:57,910 you may think you've had some really 35 00:01:57,910 --> 00:02:03,330 rough days stuck in gridlock traffic 36 00:02:03,330 --> 00:02:05,920 dodging a sea of humanity on the way to 37 00:02:05,920 --> 00:02:09,280 work or trapped in a torrential downpour 38 00:02:09,280 --> 00:02:13,930 or blizzard but they can't even begin to 39 00:02:13,930 --> 00:02:16,690 compare to the seven worst days on 40 00:02:16,690 --> 00:02:19,590 planet Earth 41 00:02:21,970 --> 00:02:24,320 throughout its history Earth has 42 00:02:24,320 --> 00:02:26,630 experienced some really bad days days 43 00:02:26,630 --> 00:02:28,690 that have killed off life created life 44 00:02:28,690 --> 00:02:30,890 restructured the planet as a whole 45 00:02:30,890 --> 00:02:32,870 all of this together has formed the 46 00:02:32,870 --> 00:02:34,700 earth that we live on today but during 47 00:02:34,700 --> 00:02:36,320 those really bad days we certainly 48 00:02:36,320 --> 00:02:39,530 wouldn't want to be here from our point 49 00:02:39,530 --> 00:02:41,690 of view Earth has been through some 50 00:02:41,690 --> 00:02:44,480 pretty rough days catastrophic impacts 51 00:02:44,480 --> 00:02:46,580 that have really changed the face of the 52 00:02:46,580 --> 00:02:49,520 planet and changed the makeup of the 53 00:02:49,520 --> 00:02:51,050 flora and fauna the animals and plants 54 00:02:51,050 --> 00:02:52,750 on the planet 55 00:02:52,750 --> 00:02:55,850 one of Earth's worst days came early in 56 00:02:55,850 --> 00:02:58,250 its history when an uninvited guest 57 00:02:58,250 --> 00:03:00,430 barged into our neighborhood and 58 00:03:00,430 --> 00:03:03,290 threatened to destroy the planet before 59 00:03:03,290 --> 00:03:07,030 life had a chance to blossom 60 00:03:07,680 --> 00:03:10,409 blasting in as the seventh worst day on 61 00:03:10,409 --> 00:03:14,599 earth the Theia impact 62 00:03:19,970 --> 00:03:22,470 about four and a half billion years ago 63 00:03:22,470 --> 00:03:27,230 our solar system was a battle zone 64 00:03:28,520 --> 00:03:32,310 giant boulders collided and coalesced to 65 00:03:32,310 --> 00:03:34,670 form planets 66 00:03:35,250 --> 00:03:39,630 infant earth took hit after searing hit 67 00:03:39,630 --> 00:03:42,250 if we could somehow magically transport 68 00:03:42,250 --> 00:03:43,660 ourselves back in time to be on the 69 00:03:43,660 --> 00:03:45,310 early earth it'd be very interesting I 70 00:03:45,310 --> 00:03:46,900 think to watch one of these large impact 71 00:03:46,900 --> 00:03:49,630 events the surface of the earth itself 72 00:03:49,630 --> 00:03:51,820 was probably heated to a near molten 73 00:03:51,820 --> 00:03:54,460 state the atmosphere would be very dusty 74 00:03:54,460 --> 00:03:57,280 it would be very hot so it'd be a very 75 00:03:57,280 --> 00:03:59,320 alien world to us one that we actually 76 00:03:59,320 --> 00:04:01,240 couldn't survive on just standing like 77 00:04:01,240 --> 00:04:04,210 we are here today pounded by incoming 78 00:04:04,210 --> 00:04:07,480 rocks earth slowly grew to nearly its 79 00:04:07,480 --> 00:04:11,260 present size developing a solid crust a 80 00:04:11,260 --> 00:04:15,250 thick mantle an iron core and a hot 81 00:04:15,250 --> 00:04:19,239 stormy atmosphere some speculate that 82 00:04:19,239 --> 00:04:22,480 life may have taken a tenuous hold but 83 00:04:22,480 --> 00:04:25,540 then disaster 84 00:04:25,540 --> 00:04:28,450 a neighboring planet named Theia had 85 00:04:28,450 --> 00:04:31,260 been edging into Earth's orbital paths 86 00:04:31,260 --> 00:04:33,850 the intrusion ended in the most 87 00:04:33,850 --> 00:04:37,810 disastrous way imaginable a collision of 88 00:04:37,810 --> 00:04:41,710 worlds was a very violent event you can 89 00:04:41,710 --> 00:04:44,380 imagine something the mass of Mars about 90 00:04:44,380 --> 00:04:45,640 ten percent the mass of the earth 91 00:04:45,640 --> 00:04:48,640 lacking in from space and blowing all 92 00:04:48,640 --> 00:04:52,030 this material in whatever was on the 93 00:04:52,030 --> 00:04:54,730 earth at that time was radically changed 94 00:04:54,730 --> 00:04:58,080 by this event 95 00:04:58,510 --> 00:05:01,390 when a mars-sized object whacked into 96 00:05:01,390 --> 00:05:03,280 the earth that was a bad day on earth 97 00:05:03,280 --> 00:05:04,960 had anything been there it definitely 98 00:05:04,960 --> 00:05:08,070 wouldn't have survived 99 00:05:08,070 --> 00:05:10,530 it took hours for the full scope of the 100 00:05:10,530 --> 00:05:14,160 catastrophe to unfold as the cores of 101 00:05:14,160 --> 00:05:16,260 the two planets melded Earth's 102 00:05:16,260 --> 00:05:20,640 atmosphere was blasted into space its 103 00:05:20,640 --> 00:05:23,520 crust liquefied at over 2,000 degrees 104 00:05:23,520 --> 00:05:27,810 Fahrenheit and vast portions of both 105 00:05:27,810 --> 00:05:30,300 Earth's and theia's Mantle's were 106 00:05:30,300 --> 00:05:34,860 ejected into orbit it's not at all like 107 00:05:34,860 --> 00:05:36,960 what you see in the movies you can sit 108 00:05:36,960 --> 00:05:38,910 down have a cup of coffee and it's still 109 00:05:38,910 --> 00:05:41,340 going on these are you know big objects 110 00:05:41,340 --> 00:05:43,290 take a long time to incur so these 111 00:05:43,290 --> 00:05:45,180 aren't the normal flashes do you think 112 00:05:45,180 --> 00:05:48,560 about a bullets hitting a wall 113 00:05:48,800 --> 00:05:52,039 the plume of ejected material created a 114 00:05:52,039 --> 00:05:55,340 vast orbital ring before coalescing into 115 00:05:55,340 --> 00:05:58,940 a new companion for the earth the 116 00:05:58,940 --> 00:06:03,470 newborn moon that fully fledged planet 117 00:06:03,470 --> 00:06:06,199 merged with the earth iron cores would 118 00:06:06,199 --> 00:06:08,030 have come together and the silicate 119 00:06:08,030 --> 00:06:11,509 Mantle's were left on the earth and also 120 00:06:11,509 --> 00:06:14,270 accreted into a disc that was orbiting 121 00:06:14,270 --> 00:06:16,580 the earth 122 00:06:16,580 --> 00:06:19,950 this disk most of it came back and 123 00:06:19,950 --> 00:06:21,720 crashed back on to the earth but then a 124 00:06:21,720 --> 00:06:25,380 portion of it reformed and over time has 125 00:06:25,380 --> 00:06:29,030 been pushed out and has become the moon 126 00:06:29,310 --> 00:06:31,500 it took about a hundred fifty million 127 00:06:31,500 --> 00:06:34,110 years for earth to stabilize and it's 128 00:06:34,110 --> 00:06:37,770 molten crust to reharden but although 129 00:06:37,770 --> 00:06:40,140 the Theia impact was a very bad day on 130 00:06:40,140 --> 00:06:44,070 earth it was a very good day for its 131 00:06:44,070 --> 00:06:48,750 ability to sustain life when the moon 132 00:06:48,750 --> 00:06:51,570 formed it's stabilized Earth's axis of 133 00:06:51,570 --> 00:06:54,150 rotation otherwise gravitational tugs 134 00:06:54,150 --> 00:06:56,070 from other planets would have caused it 135 00:06:56,070 --> 00:06:58,200 to chaotically very and that would have 136 00:06:58,200 --> 00:07:01,840 been bad for long-term climate stability 137 00:07:01,840 --> 00:07:03,560 [Music] 138 00:07:03,560 --> 00:07:06,390 what do we even have life as we know it 139 00:07:06,390 --> 00:07:08,160 if that impact had not taken place 140 00:07:08,160 --> 00:07:10,560 without a moon you could really have a 141 00:07:10,560 --> 00:07:13,650 case where your tropics within hundreds 142 00:07:13,650 --> 00:07:16,320 of thousands of years could rotate and 143 00:07:16,320 --> 00:07:19,110 become the Arctic or the Antarctic and 144 00:07:19,110 --> 00:07:21,860 you kill everything 145 00:07:23,099 --> 00:07:26,319 with the impact over in the moon now 146 00:07:26,319 --> 00:07:29,169 providing orbital stability the stage 147 00:07:29,169 --> 00:07:33,399 seems set for a quiet future but that 148 00:07:33,399 --> 00:07:36,669 was not to be before the plants you've 149 00:07:36,669 --> 00:07:39,819 won the moon never is happy and all of a 150 00:07:39,819 --> 00:07:42,219 sudden something terrible happens 151 00:07:42,219 --> 00:07:44,529 earth was suddenly caught in the 152 00:07:44,529 --> 00:07:45,129 crossfire 153 00:07:45,129 --> 00:07:49,509 once again number six on our countdown 154 00:07:49,509 --> 00:07:53,180 of worst days the late heavy bombardment 155 00:07:53,180 --> 00:07:57,180 [Music] 156 00:07:59,210 --> 00:08:01,260 approximately a hundred fifty million 157 00:08:01,260 --> 00:08:04,140 years after the Theia impact the Earth's 158 00:08:04,140 --> 00:08:08,220 crust cooled some speculate that early 159 00:08:08,220 --> 00:08:11,720 oceans and even life may have evolved 160 00:08:11,720 --> 00:08:14,880 but another Cataclysm would wipe the 161 00:08:14,880 --> 00:08:17,690 slate clean 162 00:08:18,439 --> 00:08:20,929 in the far reaches of the solar system 163 00:08:20,929 --> 00:08:23,869 the orbits of the outer gas giants began 164 00:08:23,869 --> 00:08:27,319 to fluctuate disrupting vast swarms of 165 00:08:27,319 --> 00:08:31,789 asteroids and comets trillions broke 166 00:08:31,789 --> 00:08:33,769 loose from their orbits and plunged 167 00:08:33,769 --> 00:08:35,979 inwards toward the rocky planets 168 00:08:35,979 --> 00:08:38,740 launching an era of fiery destruction 169 00:08:38,740 --> 00:08:42,939 known as the late heavy bombardment 170 00:08:43,980 --> 00:08:47,950 we know asteroids the size of Texas hit 171 00:08:47,950 --> 00:08:51,430 the earth any impactor that big costs 172 00:08:51,430 --> 00:08:53,570 the entire ocean to go away 173 00:08:53,570 --> 00:08:56,629 [Music] 174 00:08:56,930 --> 00:08:59,610 we sterilize the earth over and over and 175 00:08:59,610 --> 00:09:01,890 over so the inference we have is that 176 00:09:01,890 --> 00:09:05,190 life evolved over and over and over just 177 00:09:05,190 --> 00:09:07,500 to be snuffed out again by these large 178 00:09:07,500 --> 00:09:12,150 impacts the relentless bombardment 179 00:09:12,150 --> 00:09:14,910 gouged out craters thousands of miles 180 00:09:14,910 --> 00:09:18,990 wide and the hits just kept coming for 181 00:09:18,990 --> 00:09:22,910 at least 200 million years 182 00:09:25,480 --> 00:09:28,730 today billions of years of erosion and 183 00:09:28,730 --> 00:09:31,430 shifting plate tectonics have erased any 184 00:09:31,430 --> 00:09:33,530 trace of the Cataclysm from the Earth's 185 00:09:33,530 --> 00:09:35,890 surface 186 00:09:36,440 --> 00:09:39,439 [Music] 187 00:09:39,439 --> 00:09:42,029 but it's a different story on the 188 00:09:42,029 --> 00:09:48,959 cratered face of the moon we can see 189 00:09:48,959 --> 00:09:51,629 very clearly its record on the face of 190 00:09:51,629 --> 00:09:54,180 the moon the lava-filled basins were 191 00:09:54,180 --> 00:09:56,879 formed during the giant impact events 192 00:09:56,879 --> 00:09:57,930 that occurred during the late heavy 193 00:09:57,930 --> 00:10:01,110 bombardment and so we know that large 194 00:10:01,110 --> 00:10:05,360 objects hit the earth during this time 195 00:10:05,720 --> 00:10:08,910 but this celestial rain of fire may have 196 00:10:08,910 --> 00:10:10,470 had a silver lining 197 00:10:10,470 --> 00:10:14,910 literally new evidence suggests the late 198 00:10:14,910 --> 00:10:16,139 heavy bombardment 199 00:10:16,139 --> 00:10:18,269 delivered precious metals to the surface 200 00:10:18,269 --> 00:10:22,529 of Earth things like silver gold and 201 00:10:22,529 --> 00:10:25,279 platinum 202 00:10:25,520 --> 00:10:27,740 Earth's original store of these elements 203 00:10:27,740 --> 00:10:30,830 had sunk into its molten iron core as 204 00:10:30,830 --> 00:10:35,840 the planet slowly cooled but now with 205 00:10:35,840 --> 00:10:38,780 our planet already solidified this new 206 00:10:38,780 --> 00:10:41,330 supply of materials remained near the 207 00:10:41,330 --> 00:10:44,480 surface able to be mined by future 208 00:10:44,480 --> 00:10:48,500 humans today's technologies depend on a 209 00:10:48,500 --> 00:10:51,320 lot of the heavy elements that were 210 00:10:51,320 --> 00:10:53,660 delivered to the earth through impacts 211 00:10:53,660 --> 00:10:56,900 so it may have been very difficult for 212 00:10:56,900 --> 00:10:58,850 the life if there were life on Earth 213 00:10:58,850 --> 00:11:01,070 during the heavy bombardment but it was 214 00:11:01,070 --> 00:11:03,530 very good for the Earth's crust to have 215 00:11:03,530 --> 00:11:05,480 all of these materials that we now 216 00:11:05,480 --> 00:11:07,970 depend on delivered to the surface of 217 00:11:07,970 --> 00:11:12,080 Earth through impacts the late heavy 218 00:11:12,080 --> 00:11:15,470 bombardment was Earth's true baptism by 219 00:11:15,470 --> 00:11:17,500 fire 220 00:11:17,760 --> 00:11:20,760 but now as we reach number five in our 221 00:11:20,760 --> 00:11:23,000 countdown of the planet's worst days 222 00:11:23,000 --> 00:11:26,520 earth catches the worst cold in history 223 00:11:26,520 --> 00:11:30,990 a climactic crisis so chilling that life 224 00:11:30,990 --> 00:11:33,960 itself was in danger of being frozen in 225 00:11:33,960 --> 00:11:36,710 its tracks 226 00:11:39,210 --> 00:11:42,589 [Music] 227 00:11:42,589 --> 00:11:45,720 both the Theia impact and the late heavy 228 00:11:45,720 --> 00:11:50,779 bombardment turned earth into an inferno 229 00:11:50,810 --> 00:11:54,020 but now as we continue our countdown of 230 00:11:54,020 --> 00:11:56,960 the seven worst days on earth we skate 231 00:11:56,960 --> 00:12:00,080 forward in time to a catastrophe not of 232 00:12:00,080 --> 00:12:06,890 fire but of all-encompassing ice number 233 00:12:06,890 --> 00:12:09,800 five on our countdown the frozen 234 00:12:09,800 --> 00:12:14,500 Cataclysm known as snowball earth 235 00:12:17,670 --> 00:12:21,160 we had these bad days and snowball earth 236 00:12:21,160 --> 00:12:24,100 is much longer than a bad day is a bad 237 00:12:24,100 --> 00:12:26,710 hundreds of thousands of years snowball 238 00:12:26,710 --> 00:12:28,570 earth is that the planet that was a 239 00:12:28,570 --> 00:12:31,000 snowball it cools enough that the oceans 240 00:12:31,000 --> 00:12:35,500 freeze down to 10 feet 20 50 feet thick 241 00:12:35,500 --> 00:12:38,140 imagine the Arctic sea ice we see now 242 00:12:38,140 --> 00:12:41,050 except the whole planet has that during 243 00:12:41,050 --> 00:12:43,930 a typical Ice Age glaciers invade the 244 00:12:43,930 --> 00:12:46,480 temperate zones often reaching as far 245 00:12:46,480 --> 00:12:51,160 south as modern New York or Paris but 246 00:12:51,160 --> 00:12:53,800 during snowball earth but glaciers just 247 00:12:53,800 --> 00:12:56,260 kept coming until they had encircled the 248 00:12:56,260 --> 00:12:59,020 entire planet and frozen the oceans to a 249 00:12:59,020 --> 00:13:02,370 depth of up to a mile 250 00:13:02,579 --> 00:13:04,920 as average temperatures plunged to minus 251 00:13:04,920 --> 00:13:08,970 75 degrees Fahrenheit the equator grew 252 00:13:08,970 --> 00:13:11,879 is cold then as the South Pole is today 253 00:13:11,879 --> 00:13:15,779 and this global deep freeze may have 254 00:13:15,779 --> 00:13:20,579 happened not once but twice the first 255 00:13:20,579 --> 00:13:24,259 episode beginning 2.4 billion years ago 256 00:13:24,259 --> 00:13:26,790 during the snowball earth face the 257 00:13:26,790 --> 00:13:29,579 entire earth has a climate quite similar 258 00:13:29,579 --> 00:13:31,769 to modern-day Antarctica it's extremely 259 00:13:31,769 --> 00:13:35,089 cold extremely dry extremely windy 260 00:13:35,089 --> 00:13:37,379 extremely unhospitable 261 00:13:37,379 --> 00:13:39,980 to life 262 00:13:40,150 --> 00:13:43,120 the snowball earth hypothesis helps 263 00:13:43,120 --> 00:13:44,830 explain the discovery of glacial 264 00:13:44,830 --> 00:13:47,350 deposits than areas that were once at 265 00:13:47,350 --> 00:13:51,460 the equator it's theorized that as the 266 00:13:51,460 --> 00:13:53,140 glaciers marched on from the polar 267 00:13:53,140 --> 00:13:55,690 regions they reflected sunlight back 268 00:13:55,690 --> 00:13:58,480 into space and created a powerful 269 00:13:58,480 --> 00:14:01,050 feedback loop turning the thermostat 270 00:14:01,050 --> 00:14:04,750 relentlessly lower if the polar regions 271 00:14:04,750 --> 00:14:06,700 get too large as the snow and highly 272 00:14:06,700 --> 00:14:09,400 reflective ice coatings get too far down 273 00:14:09,400 --> 00:14:12,550 in latitude they reflect more light back 274 00:14:12,550 --> 00:14:15,670 into space the earth gets cooler the ice 275 00:14:15,670 --> 00:14:17,800 goes closer and closer closer to the 276 00:14:17,800 --> 00:14:19,270 equator so it's not to be kind of a 277 00:14:19,270 --> 00:14:22,060 runaway processed ELISA is a freezer of 278 00:14:22,060 --> 00:14:26,980 the earth but what caused the first 279 00:14:26,980 --> 00:14:30,310 snowball earth scientists think the 280 00:14:30,310 --> 00:14:32,770 culprit actually may have been life 281 00:14:32,770 --> 00:14:35,430 itself 282 00:14:35,470 --> 00:14:37,940 the gas that was most prevalent when 283 00:14:37,940 --> 00:14:39,470 life first appeared on the earth was an 284 00:14:39,470 --> 00:14:42,320 oxygen it was methane creatures at that 285 00:14:42,320 --> 00:14:45,530 time single-celled bacteria would have 286 00:14:45,530 --> 00:14:47,600 used methane as part of their normal 287 00:14:47,600 --> 00:14:50,560 living processes 288 00:14:51,350 --> 00:14:54,060 methane is a phenomenal greenhouse gas 289 00:14:54,060 --> 00:14:55,740 so if you had a lot of methane in the 290 00:14:55,740 --> 00:14:57,960 atmosphere you had likely very warm 291 00:14:57,960 --> 00:15:00,430 temperatures 292 00:15:00,430 --> 00:15:04,390 but 2.4 billion years ago a new group of 293 00:15:04,390 --> 00:15:06,880 underwater microbes began absorbing 294 00:15:06,880 --> 00:15:10,200 energy from the Sun in a process called 295 00:15:10,200 --> 00:15:14,770 photosynthesis by converting carbon 296 00:15:14,770 --> 00:15:18,089 dioxide and water into energy 297 00:15:18,089 --> 00:15:20,620 photosynthesis polluted the earth with a 298 00:15:20,620 --> 00:15:25,330 toxic new waste product oxygen vast 299 00:15:25,330 --> 00:15:28,260 amounts of it 300 00:15:28,870 --> 00:15:31,810 prior to 2.4 billion years ago oxygen 301 00:15:31,810 --> 00:15:33,730 was a poison and any life that was on 302 00:15:33,730 --> 00:15:35,740 earth did not use oxygen it was 303 00:15:35,740 --> 00:15:39,010 considered a waste gas all of that life 304 00:15:39,010 --> 00:15:41,920 that didn't like oxygen was exposed to 305 00:15:41,920 --> 00:15:44,500 this rich oxygen environment and it 306 00:15:44,500 --> 00:15:46,560 caused a great deal of stress 307 00:15:46,560 --> 00:15:49,630 methane creatures were happy to live in 308 00:15:49,630 --> 00:15:51,790 this oxygen free world and when oxygen 309 00:15:51,790 --> 00:15:54,040 finally does appear it was like the 310 00:15:54,040 --> 00:15:58,290 worst calamity in their history as 311 00:15:58,290 --> 00:16:01,600 oxygen flooded the world it oxidized 312 00:16:01,600 --> 00:16:04,380 methane turning it into carbon dioxide 313 00:16:04,380 --> 00:16:07,420 the methane consuming creatures died off 314 00:16:07,420 --> 00:16:10,240 been a fast extinction event called the 315 00:16:10,240 --> 00:16:13,450 great oxygen catastrophe and as earth 316 00:16:13,450 --> 00:16:16,230 lost its warming blanket of methane gas 317 00:16:16,230 --> 00:16:20,380 the planet froze over 318 00:16:20,380 --> 00:16:22,960 but if oxygen-producing life was the 319 00:16:22,960 --> 00:16:25,090 primary trigger of the first snowball 320 00:16:25,090 --> 00:16:28,510 earth that life now needed to find a 321 00:16:28,510 --> 00:16:31,180 warm place to escape the disaster it had 322 00:16:31,180 --> 00:16:33,450 caused 323 00:16:34,580 --> 00:16:36,589 the earth at that time was even more 324 00:16:36,589 --> 00:16:39,800 energetic tectonic Li than it is now the 325 00:16:39,800 --> 00:16:41,750 formation of the earth produced enormous 326 00:16:41,750 --> 00:16:44,570 heat that heat comes to the surface it's 327 00:16:44,570 --> 00:16:47,300 slowing but back then many more 328 00:16:47,300 --> 00:16:49,940 volcanoes around every volcano that 329 00:16:49,940 --> 00:16:51,649 would have been this melted lake-like 330 00:16:51,649 --> 00:16:54,100 zone where life could have thrived 331 00:16:54,100 --> 00:16:56,149 [Music] 332 00:16:56,149 --> 00:16:58,800 to show how volcanism could have carved 333 00:16:58,800 --> 00:17:02,490 out cozy niches for life all you need is 334 00:17:02,490 --> 00:17:07,100 a blowtorch and a big ball of ice 335 00:17:07,730 --> 00:17:10,530 we're here at carving ice and ice house 336 00:17:10,530 --> 00:17:13,169 owned by Roland Hernandez an amazing ice 337 00:17:13,169 --> 00:17:15,179 sculptor who's created for us his 338 00:17:15,179 --> 00:17:17,669 hemisphere of solid ice which represents 339 00:17:17,669 --> 00:17:19,949 snowball earth we've placed it up here 340 00:17:19,949 --> 00:17:21,600 on this dolly so that we can heat it 341 00:17:21,600 --> 00:17:23,669 from below with an industrial blowtorch 342 00:17:23,669 --> 00:17:26,069 to represent the type of heating that we 343 00:17:26,069 --> 00:17:28,079 would experience on snowball earth from 344 00:17:28,079 --> 00:17:31,580 volcanism deep beneath the surface 345 00:17:37,740 --> 00:17:42,300 [Music] 346 00:17:42,300 --> 00:17:44,770 scientists suspected the extreme heat 347 00:17:44,770 --> 00:17:46,840 pressure generated by volcanism beneath 348 00:17:46,840 --> 00:17:49,150 the earth's surface would have created 349 00:17:49,150 --> 00:17:51,580 cracks in the ice for life to take 350 00:17:51,580 --> 00:17:52,490 refuge 351 00:17:52,490 --> 00:17:54,190 [Applause] 352 00:17:54,190 --> 00:17:59,430 [Music] 353 00:17:59,430 --> 00:18:02,200 okay so you can see how the cracks have 354 00:18:02,200 --> 00:18:04,180 formed all throughout the ice along the 355 00:18:04,180 --> 00:18:06,640 top here these are very similar to the 356 00:18:06,640 --> 00:18:08,650 types of cracks that would form during a 357 00:18:08,650 --> 00:18:10,570 snowball earth event it's in these 358 00:18:10,570 --> 00:18:12,760 cracks where you can get the mixture of 359 00:18:12,760 --> 00:18:14,620 a little bit of liquid a little bit of 360 00:18:14,620 --> 00:18:16,900 heat a little bit of chemistry in other 361 00:18:16,900 --> 00:18:18,420 words the perfect ingredients for 362 00:18:18,420 --> 00:18:20,800 generating an environment where life can 363 00:18:20,800 --> 00:18:28,030 take root and even thrive volcanism 364 00:18:28,030 --> 00:18:30,460 wasn't just key to life survival during 365 00:18:30,460 --> 00:18:33,240 snowball earth 366 00:18:33,539 --> 00:18:36,419 it also may have forced the glaciers to 367 00:18:36,419 --> 00:18:39,749 finally retreat so you've got all of 368 00:18:39,749 --> 00:18:41,369 these gases that are coming out of the 369 00:18:41,369 --> 00:18:44,159 volcanoes things like water vapor carbon 370 00:18:44,159 --> 00:18:47,309 dioxide sulfur dioxide for example which 371 00:18:47,309 --> 00:18:49,169 are escaping into the atmosphere and 372 00:18:49,169 --> 00:18:51,809 over time over tens of millions of years 373 00:18:51,809 --> 00:18:53,729 you're building up these levels of 374 00:18:53,729 --> 00:18:56,789 greenhouse gases at some point is going 375 00:18:56,789 --> 00:18:58,979 to get so warm in the atmosphere that 376 00:18:58,979 --> 00:19:02,580 the ice begins to melt both episodes of 377 00:19:02,580 --> 00:19:03,659 snowball earth 378 00:19:03,659 --> 00:19:08,009 the first 2.4 billion years ago and the 379 00:19:08,009 --> 00:19:11,460 second 600 million years ago placed 380 00:19:11,460 --> 00:19:16,259 profound stresses on early life but 381 00:19:16,259 --> 00:19:19,080 oddly both were followed by enormous 382 00:19:19,080 --> 00:19:24,869 flowerings of new species we know from 383 00:19:24,869 --> 00:19:26,999 the sedimentary record that just before 384 00:19:26,999 --> 00:19:29,549 animals bloomed into existence an 385 00:19:29,549 --> 00:19:32,340 enormous amount of phosphorous came into 386 00:19:32,340 --> 00:19:34,049 the ocean there are big rocks of 387 00:19:34,049 --> 00:19:36,869 phosphorous they eroded as that erosion 388 00:19:36,869 --> 00:19:38,940 occurred phosphorous levels in the ocean 389 00:19:38,940 --> 00:19:42,299 rose all of a sudden life is able to 390 00:19:42,299 --> 00:19:46,379 just bloom this may have really caused 391 00:19:46,379 --> 00:19:49,169 the diversification two times on the 392 00:19:49,169 --> 00:19:51,509 microbial world of 2.3 billion years ago 393 00:19:51,509 --> 00:19:54,840 but more importantly to us it really 394 00:19:54,840 --> 00:19:57,119 probably helped the diversification of 395 00:19:57,119 --> 00:20:01,789 animals at 600 million years ago 396 00:20:02,700 --> 00:20:05,410 although snowball earth produced some of 397 00:20:05,410 --> 00:20:08,260 the planet's harshest weather life not 398 00:20:08,260 --> 00:20:11,080 only managed to survive it bounced back 399 00:20:11,080 --> 00:20:13,420 stronger than ever which is why this 400 00:20:13,420 --> 00:20:16,750 disaster only ranks as number five on 401 00:20:16,750 --> 00:20:21,340 our list of worst days but as the 402 00:20:21,340 --> 00:20:25,300 countdown continues forensic evidence is 403 00:20:25,300 --> 00:20:28,090 finally emerging that just may explain a 404 00:20:28,090 --> 00:20:32,679 far deadlier Cataclysm a mass killing 405 00:20:32,679 --> 00:20:35,410 spree that stands as the oldest murder 406 00:20:35,410 --> 00:20:39,300 mystery on the planet 407 00:20:44,780 --> 00:20:47,520 so far on our countdown of the seven 408 00:20:47,520 --> 00:20:50,560 worst days on earth 409 00:20:50,560 --> 00:20:52,990 we've seen our planet battered during 410 00:20:52,990 --> 00:20:55,740 the moon-forming impact 411 00:20:55,800 --> 00:21:00,170 baked by the late heavy bombardment and 412 00:21:00,170 --> 00:21:03,150 almost completely frozen over by 413 00:21:03,150 --> 00:21:07,440 snowball earth now we travel forward 414 00:21:07,440 --> 00:21:10,650 over a hundred million years as the 415 00:21:10,650 --> 00:21:12,870 world is rocked by one of the greatest 416 00:21:12,870 --> 00:21:17,970 mass killings in its history number four 417 00:21:17,970 --> 00:21:28,410 on our list the Ordovician extinction in 418 00:21:28,410 --> 00:21:32,480 the billions of years of life on Earth 419 00:21:32,480 --> 00:21:36,060 99% of all species that ever lived have 420 00:21:36,060 --> 00:21:39,750 ultimately vanished mostly due to five 421 00:21:39,750 --> 00:21:41,630 mass extinction events 422 00:21:41,630 --> 00:21:43,470 [Music] 423 00:21:43,470 --> 00:21:45,600 the first was during the Ordovician 424 00:21:45,600 --> 00:21:52,259 period 450 million years ago the mass 425 00:21:52,259 --> 00:21:54,960 extinction during the Ordovician is the 426 00:21:54,960 --> 00:21:56,700 most mysterious of the so-called big 427 00:21:56,700 --> 00:21:59,190 five simply because it was the one that 428 00:21:59,190 --> 00:22:02,039 was the oldest everyone after that was 429 00:22:02,039 --> 00:22:03,840 closer to us in time and the further 430 00:22:03,840 --> 00:22:06,419 back in time you go the more fuzzy our 431 00:22:06,419 --> 00:22:10,379 scientific view of the past is during 432 00:22:10,379 --> 00:22:12,509 the Ordovician period the globe was 433 00:22:12,509 --> 00:22:15,210 covered with three major oceans and four 434 00:22:15,210 --> 00:22:17,140 super continents 435 00:22:17,140 --> 00:22:18,650 [Music] 436 00:22:18,650 --> 00:22:22,100 the land was still barren but the oceans 437 00:22:22,100 --> 00:22:25,550 teemed with life including brilliant 438 00:22:25,550 --> 00:22:30,500 corals and the planets first fish then a 439 00:22:30,500 --> 00:22:33,790 mysterious Cataclysm swept the seas and 440 00:22:33,790 --> 00:22:39,680 60% of life on Earth vanished there's a 441 00:22:39,680 --> 00:22:41,930 couple of possibilities number one it 442 00:22:41,930 --> 00:22:43,730 got cold again so why would have gotten 443 00:22:43,730 --> 00:22:45,770 cold well it could have been that plate 444 00:22:45,770 --> 00:22:48,680 tectonics moved all of the formerly warm 445 00:22:48,680 --> 00:22:51,620 continents down to the polar regions and 446 00:22:51,620 --> 00:22:53,090 that dropped the temperature of 447 00:22:53,090 --> 00:22:58,250 everything for years scientists blamed 448 00:22:58,250 --> 00:23:00,340 the Ordovician extinction on a 449 00:23:00,340 --> 00:23:04,550 devastating ice age but now some 450 00:23:04,550 --> 00:23:06,980 researchers propose that the mass killer 451 00:23:06,980 --> 00:23:08,809 could have been something from the 452 00:23:08,809 --> 00:23:13,880 cosmos like a gamma-ray burst the 453 00:23:13,880 --> 00:23:17,290 biggest blasts in the universe 454 00:23:17,970 --> 00:23:20,370 a gamma-ray burst is a colossal 455 00:23:20,370 --> 00:23:22,590 explosion of a star that occurs 456 00:23:22,590 --> 00:23:25,680 asymmetrically there are two oppositely 457 00:23:25,680 --> 00:23:27,800 directed beams of very energetic 458 00:23:27,800 --> 00:23:30,570 high-speed particles and radiation that 459 00:23:30,570 --> 00:23:32,340 goes zipping through space kind of like 460 00:23:32,340 --> 00:23:35,850 a laser beam if that beam is aimed right 461 00:23:35,850 --> 00:23:38,250 at earth that can cause significant 462 00:23:38,250 --> 00:23:44,310 damage here a large burst would vaporize 463 00:23:44,310 --> 00:23:46,680 a third of a planet's protective ozone 464 00:23:46,680 --> 00:23:49,500 layer and creatures on the side of the 465 00:23:49,500 --> 00:23:52,080 earth facing the onslaught would suffer 466 00:23:52,080 --> 00:23:55,760 lethal radiation exposure 467 00:23:55,770 --> 00:23:57,840 the destructive energy of a gamma-ray 468 00:23:57,840 --> 00:24:02,330 burst can be demonstrated here on earth 469 00:24:02,330 --> 00:24:04,800 here's our globe representing the earth 470 00:24:04,800 --> 00:24:07,080 at the end of the Ordovician period a 471 00:24:07,080 --> 00:24:09,390 time when one group of scientists thinks 472 00:24:09,390 --> 00:24:11,130 that a gamma-ray burst may have 473 00:24:11,130 --> 00:24:13,050 triggered a mass extinction the paper 474 00:24:13,050 --> 00:24:15,120 represents the Earth's ozone layer and 475 00:24:15,120 --> 00:24:17,400 the gamma-ray burst is represented by 476 00:24:17,400 --> 00:24:20,540 this propane torch 477 00:24:22,530 --> 00:24:32,170 [Music] 478 00:24:32,170 --> 00:24:35,990 and seconds worth that's all they say it 479 00:24:35,990 --> 00:24:38,390 would take to destroy about a third of 480 00:24:38,390 --> 00:24:41,720 the Earth's ozone so of course the gamma 481 00:24:41,720 --> 00:24:43,760 ray burst didn't actually torch the 482 00:24:43,760 --> 00:24:46,490 earth but it did destroy the ozone that 483 00:24:46,490 --> 00:24:48,140 it encountered and it would have messed 484 00:24:48,140 --> 00:24:49,430 with the chemistry of the ozone 485 00:24:49,430 --> 00:24:52,040 molecules on this side of the globe and 486 00:24:52,040 --> 00:24:53,870 when the ozone was destroyed UV 487 00:24:53,870 --> 00:24:55,730 radiation can penetrate to the surface 488 00:24:55,730 --> 00:24:58,220 and the ultraviolet radiation is very 489 00:24:58,220 --> 00:25:00,470 lethal to life it's very destructive to 490 00:25:00,470 --> 00:25:04,940 DNA so it may be that a gamma-ray burst 491 00:25:04,940 --> 00:25:07,700 destroying the ozone layer contributed 492 00:25:07,700 --> 00:25:10,130 to or maybe even triggered a mass 493 00:25:10,130 --> 00:25:13,570 extinction at the end of the Ordovician 494 00:25:15,580 --> 00:25:18,410 in addition to depleting the ozone layer 495 00:25:18,410 --> 00:25:20,960 a large gamma-ray burst 496 00:25:20,960 --> 00:25:23,330 also could have ripped apart nitrogen 497 00:25:23,330 --> 00:25:25,340 and oxygen molecules in the atmosphere 498 00:25:25,340 --> 00:25:27,890 producing a gaseous smog of nitrogen 499 00:25:27,890 --> 00:25:31,670 dioxide that blocked sunlight and set 500 00:25:31,670 --> 00:25:36,880 off a secondary disaster an ice age 501 00:25:39,830 --> 00:25:41,870 it's not clear whether that could have 502 00:25:41,870 --> 00:25:44,000 been caused by a gamma-ray burst but at 503 00:25:44,000 --> 00:25:45,800 least part of the Ordovician extinction 504 00:25:45,800 --> 00:25:48,440 seems to have been marked by a huge 505 00:25:48,440 --> 00:25:50,960 decrease in the number of surface 506 00:25:50,960 --> 00:25:53,450 dwelling creatures like on the Earth's 507 00:25:53,450 --> 00:25:55,460 surface or in the surface layers of the 508 00:25:55,460 --> 00:25:59,480 ocean that may well indicate that it was 509 00:25:59,480 --> 00:26:01,880 ultraviolet radiation that killed him 510 00:26:01,880 --> 00:26:06,040 off rather than some other factor a 511 00:26:07,060 --> 00:26:09,740 gamma-ray burst could be one explanation 512 00:26:09,740 --> 00:26:12,680 for the first mass annihilation of life 513 00:26:12,680 --> 00:26:17,510 on Earth but a startling new hypothesis 514 00:26:17,510 --> 00:26:20,830 points to a different cosmic force a 515 00:26:20,830 --> 00:26:23,060 bizarre and potentially deadly 516 00:26:23,060 --> 00:26:28,000 phenomenon known as a bow shock 517 00:26:28,120 --> 00:26:30,250 a bow shock forms when there's 518 00:26:30,250 --> 00:26:32,590 compression of material in front of a 519 00:26:32,590 --> 00:26:34,660 moving object so for example if you have 520 00:26:34,660 --> 00:26:37,270 a boat zooming along it creates a way 521 00:26:37,270 --> 00:26:39,010 the compression in front of it that then 522 00:26:39,010 --> 00:26:41,010 bends around as the boat canoes through 523 00:26:41,010 --> 00:26:43,660 well our galaxy is moving rapidly 524 00:26:43,660 --> 00:26:46,350 through space so it can compress 525 00:26:46,350 --> 00:26:49,480 intergalactic gas in front of it heating 526 00:26:49,480 --> 00:26:52,420 it up creating cosmic rays and some of 527 00:26:52,420 --> 00:26:56,610 those cosmic rays can then hit the earth 528 00:26:56,940 --> 00:26:59,830 our solar system oscillates through the 529 00:26:59,830 --> 00:27:03,340 Milky Way traveling above and below the 530 00:27:03,340 --> 00:27:06,910 main disk of the galaxy every 64 million 531 00:27:06,910 --> 00:27:10,960 years once outside the galaxy's 532 00:27:10,960 --> 00:27:14,200 protective magnetic field our planet is 533 00:27:14,200 --> 00:27:16,060 vulnerable to deadly cosmic rays 534 00:27:16,060 --> 00:27:21,700 generated by the Galactic bow shock much 535 00:27:21,700 --> 00:27:23,670 like a wakeboarder on a lake 536 00:27:23,670 --> 00:27:26,900 [Music] 537 00:27:32,610 --> 00:27:34,769 wakeboarding would be a reasonable 538 00:27:34,769 --> 00:27:38,510 example of a bow shock in space 539 00:27:41,620 --> 00:27:43,870 while the wakeboarder is well within the 540 00:27:43,870 --> 00:27:46,059 confines of the bow wake of the boat the 541 00:27:46,059 --> 00:27:47,830 water is very calm and smooth and he has 542 00:27:47,830 --> 00:27:49,960 no trouble standing up but during those 543 00:27:49,960 --> 00:27:51,460 periods when he moves out towards the 544 00:27:51,460 --> 00:27:53,200 edge of the way the water becomes a bit 545 00:27:53,200 --> 00:27:54,610 more turbulent and a bit more chaotic 546 00:27:54,610 --> 00:27:58,320 and he has trouble standing up 547 00:28:00,810 --> 00:28:04,120 the same thing is true in space for most 548 00:28:04,120 --> 00:28:06,190 of the time the earth and Sun are well 549 00:28:06,190 --> 00:28:08,470 within the protective confines of the 550 00:28:08,470 --> 00:28:10,290 Milky Way galaxy's magnetic field 551 00:28:10,290 --> 00:28:13,240 protecting it from the cosmic rays and 552 00:28:13,240 --> 00:28:14,680 other radiation that's coming in from 553 00:28:14,680 --> 00:28:17,020 the bow shock but during those periods 554 00:28:17,020 --> 00:28:19,090 when the Earth and the Sun rise above 555 00:28:19,090 --> 00:28:20,980 the Galactic plane it's much more 556 00:28:20,980 --> 00:28:22,870 vulnerable to all of these cosmic rays 557 00:28:22,870 --> 00:28:28,720 coming from the bow shot fossil records 558 00:28:28,720 --> 00:28:31,060 indicate that the biodiversity of many 559 00:28:31,060 --> 00:28:34,060 species may increase and decrease than 560 00:28:34,060 --> 00:28:37,060 62 million year cycles those cycles 561 00:28:37,060 --> 00:28:39,130 closely coinciding with the times of 562 00:28:39,130 --> 00:28:41,560 greatest exposure to cosmic rays from 563 00:28:41,560 --> 00:28:44,500 the Galactic bow shock which occur every 564 00:28:44,500 --> 00:28:48,370 64 million years could the two events be 565 00:28:48,370 --> 00:28:51,580 connected to of the mass extinctions 566 00:28:51,580 --> 00:28:53,890 happen to have occurred at about the 567 00:28:53,890 --> 00:28:56,890 time when the Sun was highest above the 568 00:28:56,890 --> 00:28:59,590 plane of our galaxy that suggests that 569 00:28:59,590 --> 00:29:01,240 there's something about that particular 570 00:29:01,240 --> 00:29:04,120 location that's special causing these 571 00:29:04,120 --> 00:29:07,020 mass extinctions 572 00:29:07,450 --> 00:29:10,940 during the Ordovician extinction earth 573 00:29:10,940 --> 00:29:12,530 could have been blasted with enough 574 00:29:12,530 --> 00:29:14,600 deadly radiation from the Galactic bow 575 00:29:14,600 --> 00:29:17,630 shock to unleash genetic mutations and 576 00:29:17,630 --> 00:29:21,410 DNA damage that wiped out over half of 577 00:29:21,410 --> 00:29:22,660 all species 578 00:29:22,660 --> 00:29:25,590 [Music] 579 00:29:25,590 --> 00:29:29,529 this is not yet a well-tested idea it's 580 00:29:29,529 --> 00:29:32,049 just out there on the drawing board but 581 00:29:32,049 --> 00:29:34,600 it could explain some of the possible 582 00:29:34,600 --> 00:29:37,950 periodicity in Earth's mass extinctions 583 00:29:37,950 --> 00:29:40,809 but while the Ordovician extinction was 584 00:29:40,809 --> 00:29:44,140 fatal to most species some grasped at 585 00:29:44,140 --> 00:29:46,960 the opportunity it's like pulling weeds 586 00:29:46,960 --> 00:29:49,270 out of a garden you sort of clean out 587 00:29:49,270 --> 00:29:52,390 and weed out and thin out that seems to 588 00:29:52,390 --> 00:29:53,770 have happened in the Ordovician mass 589 00:29:53,770 --> 00:29:56,080 extinction some creatures which died out 590 00:29:56,080 --> 00:30:00,520 allowed others to diversify the 591 00:30:00,520 --> 00:30:03,059 Ordovician was the first mass extinction 592 00:30:03,059 --> 00:30:06,840 but hardly the worst 593 00:30:07,130 --> 00:30:09,600 number three on our countdown of the 594 00:30:09,600 --> 00:30:13,320 worst days on earth it's the most famous 595 00:30:13,320 --> 00:30:17,190 die-off in prehistory but if you think 596 00:30:17,190 --> 00:30:19,830 you know what killed the dinosaurs you 597 00:30:19,830 --> 00:30:23,310 may be in for a surprise because some 598 00:30:23,310 --> 00:30:26,010 scientists now argue that the common 599 00:30:26,010 --> 00:30:29,220 explanation of a single giant impact on 600 00:30:29,220 --> 00:30:32,820 a single disastrous day is itself about 601 00:30:32,820 --> 00:30:35,060 to be blasted away 602 00:30:35,060 --> 00:30:38,670 [Music] 603 00:30:39,710 --> 00:30:42,840 in our countdown to the very worst day 604 00:30:42,840 --> 00:30:44,250 on earth 605 00:30:44,250 --> 00:30:46,350 no catastrophe has been the subject of 606 00:30:46,350 --> 00:30:48,510 more public fascination and sensational 607 00:30:48,510 --> 00:30:51,780 headlines than the bombardment that 608 00:30:51,780 --> 00:30:56,540 ultimately cleared the path for mankind 609 00:30:57,090 --> 00:31:00,360 but today controversial new hypotheses 610 00:31:00,360 --> 00:31:03,150 challenge the concept that a single 611 00:31:03,150 --> 00:31:05,700 disastrous impact wiped out the 612 00:31:05,700 --> 00:31:09,660 dinosaurs and led to the third worst day 613 00:31:09,660 --> 00:31:14,740 on earth the KT extinction 614 00:31:14,740 --> 00:31:17,880 [Music] 615 00:31:19,610 --> 00:31:21,960 sixty-five million years ago we would 616 00:31:21,960 --> 00:31:24,900 have seen a world something like Africa 617 00:31:24,900 --> 00:31:26,670 in terms of the number of animals out 618 00:31:26,670 --> 00:31:28,530 there but instead of big mammals we have 619 00:31:28,530 --> 00:31:32,100 big dinosaurs herds of Triceratops herds 620 00:31:32,100 --> 00:31:35,340 of duck-billed dinosaurs small to big 621 00:31:35,340 --> 00:31:37,950 predators the largest being t-rex 622 00:31:37,950 --> 00:31:40,540 [Music] 623 00:31:40,540 --> 00:31:43,220 dinosaurs ruled the prehistoric world 624 00:31:43,220 --> 00:31:48,200 for almost 200 million years then 625 00:31:48,200 --> 00:31:50,480 something took out two-thirds of all 626 00:31:50,480 --> 00:31:53,150 living creatures including the giant 627 00:31:53,150 --> 00:31:59,900 beasts after years of searching for 628 00:31:59,900 --> 00:32:02,690 clues most experts now agree that a 629 00:32:02,690 --> 00:32:05,600 single Cataclysm doomed the dinosaurs 630 00:32:05,600 --> 00:32:09,920 the evidence for an impact of a 631 00:32:09,920 --> 00:32:12,470 six-mile-wide asteroid 65 million years 632 00:32:12,470 --> 00:32:14,240 ago is about as good as anything gets in 633 00:32:14,240 --> 00:32:20,570 science 65 million years ago a rock the 634 00:32:20,570 --> 00:32:23,030 size of Mount Everest barreled down from 635 00:32:23,030 --> 00:32:25,130 the sky and slammed into the Yucatan 636 00:32:25,130 --> 00:32:30,250 Peninsula near modern Chicxulub Mexico 637 00:32:30,850 --> 00:32:33,470 the impact unleashed an unstoppable 638 00:32:33,470 --> 00:32:37,700 chain of destruction first locally then 639 00:32:37,700 --> 00:32:40,190 across the globe 640 00:32:40,190 --> 00:32:42,690 the Katy is an asteroid driven 641 00:32:42,690 --> 00:32:44,700 extinction a big rock from space came 642 00:32:44,700 --> 00:32:46,890 down clunked a few dinosaurs on the head 643 00:32:46,890 --> 00:32:49,710 but the kill mechanism was really the 644 00:32:49,710 --> 00:32:51,120 secondary effects of this it would have 645 00:32:51,120 --> 00:32:53,460 been dark into the atmosphere acid rain 646 00:32:53,460 --> 00:32:57,200 a change in the entire biosphere 647 00:32:57,200 --> 00:32:59,659 proponents of the single impact Theory 648 00:32:59,659 --> 00:33:03,830 point to a convincing array of evidence 649 00:33:03,830 --> 00:33:06,179 including high levels of the asteroid 650 00:33:06,179 --> 00:33:08,909 element iridium at the KT events 651 00:33:08,909 --> 00:33:12,120 geological boundary or death layer and 652 00:33:12,120 --> 00:33:15,659 of course The Smoking Gun itself the 653 00:33:15,659 --> 00:33:19,889 underwater crater in modern Mexico but 654 00:33:19,889 --> 00:33:23,760 is this cold case finally closed some 655 00:33:23,760 --> 00:33:25,919 scientists now argue the Yucatan 656 00:33:25,919 --> 00:33:29,429 asteroid had accomplices there seem to 657 00:33:29,429 --> 00:33:31,440 be various causes that can trigger these 658 00:33:31,440 --> 00:33:33,720 and in some cases several causes come 659 00:33:33,720 --> 00:33:35,580 together and sort of a confluence of bad 660 00:33:35,580 --> 00:33:37,559 circumstances to provide a particularly 661 00:33:37,559 --> 00:33:41,460 damaging extinction event millions of 662 00:33:41,460 --> 00:33:44,820 years before the KT extinction vast lava 663 00:33:44,820 --> 00:33:46,919 flows had been pouring out of the Deccan 664 00:33:46,919 --> 00:33:50,490 Traps a series of lava beds now located 665 00:33:50,490 --> 00:33:53,450 in Southwest India 666 00:33:53,450 --> 00:33:56,149 these flood basalts once spewed out 667 00:33:56,149 --> 00:33:58,519 enough magma to cover a million square 668 00:33:58,519 --> 00:34:01,909 miles and belched up a toxic brew of 669 00:34:01,909 --> 00:34:04,010 gases that could have altered the 670 00:34:04,010 --> 00:34:08,419 climate around the world that period of 671 00:34:08,419 --> 00:34:11,030 eruption is pretty coincident with the 672 00:34:11,030 --> 00:34:12,829 extinction 65 million years ago as well 673 00:34:12,829 --> 00:34:14,659 in fact they were going on for millions 674 00:34:14,659 --> 00:34:17,270 of years before the KT impact and before 675 00:34:17,270 --> 00:34:20,389 the extinctions and so perhaps could be 676 00:34:20,389 --> 00:34:23,929 a complicating factor in this scenario 677 00:34:23,929 --> 00:34:26,599 the dinosaurs received a double knockout 678 00:34:26,599 --> 00:34:28,929 blow 679 00:34:28,940 --> 00:34:31,369 first the rampant volcanism of the 680 00:34:31,369 --> 00:34:36,490 Deccan Traps then the Yucatan impact 681 00:34:38,460 --> 00:34:41,889 and a small group of dissenters goes 682 00:34:41,889 --> 00:34:45,220 even further claiming that multiple 683 00:34:45,220 --> 00:34:47,109 asteroids struck earth at roughly the 684 00:34:47,109 --> 00:34:52,359 same time 65 million years ago according 685 00:34:52,359 --> 00:34:54,879 to them the Yucatan impact wasn't the 686 00:34:54,879 --> 00:34:59,990 largest only the best documented 687 00:34:59,990 --> 00:35:02,070 some people think that there may have 688 00:35:02,070 --> 00:35:04,440 been multiple impacts a shower of 689 00:35:04,440 --> 00:35:07,350 impacts for example perhaps they came 690 00:35:07,350 --> 00:35:11,150 from a single object that broke apart 691 00:35:11,210 --> 00:35:13,830 supporters of this hypothesis point to a 692 00:35:13,830 --> 00:35:18,210 suspicious geologic feature a 370 mile 693 00:35:18,210 --> 00:35:21,540 Basin off the coast of India more than 694 00:35:21,540 --> 00:35:23,700 three times larger than the Yucatan 695 00:35:23,700 --> 00:35:27,480 impact site but controversy swirls 696 00:35:27,480 --> 00:35:30,720 around this so-called shiva crater named 697 00:35:30,720 --> 00:35:33,860 after the Hindu god of destruction 698 00:35:33,860 --> 00:35:36,480 including whether it's even a crater at 699 00:35:36,480 --> 00:35:41,220 all while this feature certainly looks 700 00:35:41,220 --> 00:35:43,440 circular and looks crater like there's 701 00:35:43,440 --> 00:35:45,480 no other evidence that it's an actual 702 00:35:45,480 --> 00:35:49,530 impact structure for some the dinosaur 703 00:35:49,530 --> 00:35:53,550 die-off debate rages on but most 704 00:35:53,550 --> 00:35:56,280 scientists agree the apocalyptic event 705 00:35:56,280 --> 00:35:58,890 was a very fortunate day for small 706 00:35:58,890 --> 00:36:01,710 mammals that were no longer dinner for 707 00:36:01,710 --> 00:36:05,370 t-rex had it not been for the KT impact 708 00:36:05,370 --> 00:36:08,160 and the volcanism that was also at the 709 00:36:08,160 --> 00:36:09,920 time of the extinction of the dinosaurs 710 00:36:09,920 --> 00:36:12,660 the mammals probably wouldn't have risen 711 00:36:12,660 --> 00:36:14,940 to the prominence that they did and 712 00:36:14,940 --> 00:36:16,770 thank heaven for the rise of mammals 713 00:36:16,770 --> 00:36:19,980 because that led to the rise of humans 714 00:36:19,980 --> 00:36:22,710 the KT extinction raises a sobering 715 00:36:22,710 --> 00:36:26,820 question could humans one day go the way 716 00:36:26,820 --> 00:36:29,390 of the dinosaurs 717 00:36:29,390 --> 00:36:32,550 that's what viewer Tom Moore from Adrian 718 00:36:32,550 --> 00:36:37,800 Michigan wanted to ask the universe will 719 00:36:37,800 --> 00:36:40,800 earth be struck again by a KT sized 720 00:36:40,800 --> 00:36:46,110 asteroid well Tom earth could definitely 721 00:36:46,110 --> 00:36:48,960 be hit by another KT size comet or 722 00:36:48,960 --> 00:36:51,600 asteroid they're out there the good news 723 00:36:51,600 --> 00:36:53,670 is we're tracking the positions of most 724 00:36:53,670 --> 00:36:56,310 of the big ones so if we ever find one 725 00:36:56,310 --> 00:36:57,570 with Earth's name written on it 726 00:36:57,570 --> 00:36:59,970 hopefully we'll be able to deflect it 727 00:36:59,970 --> 00:37:03,900 before it reaches Earth the KT event 728 00:37:03,900 --> 00:37:05,870 toppled t-rex 729 00:37:05,870 --> 00:37:09,420 but it only ranks as number 3 on our 730 00:37:09,420 --> 00:37:13,950 countdown of worst days on earth number 731 00:37:13,950 --> 00:37:16,790 2 was the mother of all extinctions the 732 00:37:16,790 --> 00:37:19,380 greatest die-off that life on Earth has 733 00:37:19,380 --> 00:37:22,980 ever suffered it's also been one of the 734 00:37:22,980 --> 00:37:26,210 biggest unsolved mysteries in science 735 00:37:26,210 --> 00:37:29,540 until now 736 00:37:35,589 --> 00:37:38,880 as we near the climax of our countdown 737 00:37:38,880 --> 00:37:42,180 we reopen one of the oldest cold cases 738 00:37:42,180 --> 00:37:46,859 an unsolved murder mystery that happened 739 00:37:46,859 --> 00:37:52,359 250 million years ago almost 200 million 740 00:37:52,359 --> 00:37:54,759 years before the downfall of the 741 00:37:54,759 --> 00:37:59,650 dinosaurs the second worst day witnessed 742 00:37:59,650 --> 00:38:01,450 the greatest mass extinction in the 743 00:38:01,450 --> 00:38:06,369 planets history a cataclysm known as the 744 00:38:06,369 --> 00:38:08,999 Great dying 745 00:38:10,170 --> 00:38:13,480 during the Permian period earth was a 746 00:38:13,480 --> 00:38:15,940 wondrous world of mammal-like reptiles 747 00:38:15,940 --> 00:38:21,580 and exotic sea creatures then 90% of all 748 00:38:21,580 --> 00:38:26,080 life disappeared from the planet this is 749 00:38:26,080 --> 00:38:28,150 a bad few hundred thousand years on 750 00:38:28,150 --> 00:38:28,960 planet Earth 751 00:38:28,960 --> 00:38:29,980 but it was certainly the most 752 00:38:29,980 --> 00:38:33,400 catastrophic more life died then than 753 00:38:33,400 --> 00:38:35,890 any time since and maybe any time before 754 00:38:35,890 --> 00:38:37,900 this was the biggest and the baddest of 755 00:38:37,900 --> 00:38:42,490 them all for decades scientists have 756 00:38:42,490 --> 00:38:45,250 sifted through Clues struggling to solve 757 00:38:45,250 --> 00:38:47,710 the mystery of the great dying when the 758 00:38:47,710 --> 00:38:49,450 survival of life itself 759 00:38:49,450 --> 00:38:52,920 seemed to hang by a thread 760 00:38:55,210 --> 00:38:57,970 one of the prime suspects a supervolcano 761 00:38:57,970 --> 00:39:00,609 that tourists Siberia opened for 762 00:39:00,609 --> 00:39:02,190 hundreds of miles 763 00:39:02,190 --> 00:39:05,579 erupted for at least a million years and 764 00:39:05,579 --> 00:39:08,349 produced the greatest lava flows ever 765 00:39:08,349 --> 00:39:12,369 known enough to bury the entire United 766 00:39:12,369 --> 00:39:15,750 States thousands of feet deep 767 00:39:15,750 --> 00:39:19,210 this wasn't a single giant volcano it 768 00:39:19,210 --> 00:39:20,859 was simply cracks in the earth and 769 00:39:20,859 --> 00:39:23,530 you're like pumping out lava it's like a 770 00:39:23,530 --> 00:39:26,710 fire hose spewing lava everywhere well 771 00:39:26,710 --> 00:39:28,329 that's certainly what killed anything in 772 00:39:28,329 --> 00:39:31,300 his way it's believed that you had these 773 00:39:31,300 --> 00:39:33,220 beds of coal on what is now Siberia 774 00:39:33,220 --> 00:39:36,460 which can have lava erupting underneath 775 00:39:36,460 --> 00:39:38,200 them burning the coal putting all sorts 776 00:39:38,200 --> 00:39:40,480 of noxious greenhouse and other toxic 777 00:39:40,480 --> 00:39:42,460 gases into the atmosphere and really 778 00:39:42,460 --> 00:39:45,900 putting strong stress onto the biosphere 779 00:39:45,900 --> 00:39:48,940 the increased global warming was fatal 780 00:39:48,940 --> 00:39:52,720 to most animals but plants usually 781 00:39:52,720 --> 00:39:56,530 thrive on carbon dioxide so why did they 782 00:39:56,530 --> 00:39:59,079 also succumb at rates that have never 783 00:39:59,079 --> 00:40:00,630 been equalled 784 00:40:00,630 --> 00:40:03,700 there's a second killer in the story 785 00:40:03,700 --> 00:40:05,650 that we think and just now discovering 786 00:40:05,650 --> 00:40:07,480 and that's the presence for the first 787 00:40:07,480 --> 00:40:10,420 time on the planet of massive amounts of 788 00:40:10,420 --> 00:40:13,270 hydrogen sulfide gas the same stuff you 789 00:40:13,270 --> 00:40:15,370 see with rotten eggs that's a true 790 00:40:15,370 --> 00:40:18,790 poison and it with the heat combined I 791 00:40:18,790 --> 00:40:20,290 think to caused this greatest of mass 792 00:40:20,290 --> 00:40:22,890 extinctions 793 00:40:23,360 --> 00:40:26,580 if the scientific jury is still debating 794 00:40:26,580 --> 00:40:27,710 the cause of the permian-triassic 795 00:40:27,710 --> 00:40:31,920 extinction no one disputes that those 796 00:40:31,920 --> 00:40:34,320 were the darkest days for life on our 797 00:40:34,320 --> 00:40:40,860 planet so far but life on Earth cannot 798 00:40:40,860 --> 00:40:43,830 and will not survive an event that 799 00:40:43,830 --> 00:40:46,740 scientists predict is as unavoidable as 800 00:40:46,740 --> 00:40:51,180 death itself the number one worst day on 801 00:40:51,180 --> 00:40:56,330 planet Earth the solar apocalypse 802 00:40:57,250 --> 00:41:01,000 in five billion years our Sun will reach 803 00:41:01,000 --> 00:41:03,950 the end of its life 804 00:41:03,950 --> 00:41:07,250 as it exhausts its nuclear fuel it will 805 00:41:07,250 --> 00:41:10,360 undergo a disastrous transformation 806 00:41:10,360 --> 00:41:15,080 bloating into a red giant star 200 times 807 00:41:15,080 --> 00:41:19,880 its original size as it swells it will 808 00:41:19,880 --> 00:41:24,710 first engulf Mercury then Venus the 809 00:41:24,710 --> 00:41:27,290 incinerated earth will either be pushed 810 00:41:27,290 --> 00:41:32,350 to a higher orbit or swallowed itself 811 00:41:32,350 --> 00:41:36,140 the good news humans won't be around the 812 00:41:36,140 --> 00:41:39,530 day our Sun incinerates service the bad 813 00:41:39,530 --> 00:41:41,869 news we will have been roasted 814 00:41:41,869 --> 00:41:44,680 long before 815 00:41:45,520 --> 00:41:49,990 the Sun gets brighter about 10% every 816 00:41:49,990 --> 00:41:53,230 billion years and so in less than a 817 00:41:53,230 --> 00:41:54,700 billion years the Sun will be bright 818 00:41:54,700 --> 00:41:56,740 enough that's predicted that it will 819 00:41:56,740 --> 00:42:00,040 pump basically all well most the carbon 820 00:42:00,040 --> 00:42:03,010 dioxide out of the atmosphere and so 821 00:42:03,010 --> 00:42:06,220 things that rely on carbon dioxide like 822 00:42:06,220 --> 00:42:07,720 plants are going to have a hard time 823 00:42:07,720 --> 00:42:14,170 surviving in a natural order as plants 824 00:42:14,170 --> 00:42:17,680 shrivel and oceans evaporate biologists 825 00:42:17,680 --> 00:42:20,740 predict a future make a mass extinction 826 00:42:20,740 --> 00:42:22,530 [Music] 827 00:42:22,530 --> 00:42:26,290 the age of animals will end in about 500 828 00:42:26,290 --> 00:42:30,430 million years we have as much time in 829 00:42:30,430 --> 00:42:33,190 the future to be alive as an animal as 830 00:42:33,190 --> 00:42:34,869 we've had in the past or halfway through 831 00:42:34,869 --> 00:42:36,440 that's a sobering thought 832 00:42:36,440 --> 00:42:39,979 [Music] 833 00:42:44,990 --> 00:42:48,990 we've seen earth smacked by the giant 834 00:42:48,990 --> 00:42:51,750 moon-forming impact strafed and 835 00:42:51,750 --> 00:42:53,850 sterilized during the late heavy 836 00:42:53,850 --> 00:42:57,480 bombardment and frozen into a giant 837 00:42:57,480 --> 00:43:00,170 snowball 838 00:43:00,490 --> 00:43:03,610 a cosmic force ravaged an ancient water 839 00:43:03,610 --> 00:43:07,260 world during the first mass extinction 840 00:43:07,260 --> 00:43:09,880 followed by a near total extinction 841 00:43:09,880 --> 00:43:12,280 during the great diamond 842 00:43:12,280 --> 00:43:14,320 and the spectacular fall of the 843 00:43:14,320 --> 00:43:16,920 dinosaurs 844 00:43:17,860 --> 00:43:20,770 what else lies in store before our 845 00:43:20,770 --> 00:43:25,590 planet is ultimately baked by the Sun 846 00:43:26,480 --> 00:43:29,089 earth will certainly continue to 847 00:43:29,089 --> 00:43:31,310 experience disasters all the way up 848 00:43:31,310 --> 00:43:32,930 until the very end 849 00:43:32,930 --> 00:43:35,060 when the Sun spread giant phase brings 850 00:43:35,060 --> 00:43:39,290 an end to the story history has proven 851 00:43:39,290 --> 00:43:42,640 that Earth is an unpredictable planet 852 00:43:42,640 --> 00:43:45,410 orbiting in a very dangerous galactic 853 00:43:45,410 --> 00:43:50,210 neighborhood to survive mankind must 854 00:43:50,210 --> 00:43:52,430 learn from the worst days of our past 855 00:43:52,430 --> 00:43:55,099 and try to prepare for whatever the 856 00:43:55,099 --> 00:43:59,240 cosmos might throw at us only by 857 00:43:59,240 --> 00:44:01,000 increasing our knowledge of the universe 858 00:44:01,000 --> 00:44:03,920 and we hope to thrive and fully enjoy 859 00:44:03,920 --> 00:44:08,119 our final 500 million years of life on 860 00:44:08,119 --> 00:44:10,390 Earth 861 00:44:10,390 --> 00:44:12,450 you