2 00:00:10,750 --> 00:00:17,571 Looking at our three Goldilocks planets; Venus, Earth, and Mars. 3 00:00:17,571 --> 00:00:22,770 Venus suffered a runaway greenhouse effect, you already know. 4 00:00:22,770 --> 00:00:27,050 And so, the water in the oceans boiled, goes into the upper atmosphere 5 00:00:27,050 --> 00:00:30,630 where the ultra-violet light breaks it apart. 6 00:00:30,630 --> 00:00:34,670 You lose the hydrogen into space, water's gone, that's it forever. 7 00:00:34,670 --> 00:00:35,780 Well, now the nail in the coffin is, 8 00:00:35,780 --> 00:00:40,300 if you have no water, you can't have any weathering. 9 00:00:40,300 --> 00:00:45,130 And so, you have broken the thermostat. 10 00:00:45,130 --> 00:00:48,080 All of the carbon gets cooked and put into the atmosphere. 11 00:00:48,080 --> 00:00:53,510 That's why the atmosphere of Venus has 70 bars of CO2. 12 00:00:53,510 --> 00:00:57,070 That's why all of Venus's carbon is in the atmosphere, 13 00:00:57,070 --> 00:01:01,270 rather than on earth where almost all of our carbon is in 14 00:01:01,270 --> 00:01:03,770 calcium carbonate or other sedimentary rocks. 15 00:01:05,260 --> 00:01:09,980 On Earth, the thermostat will eventually clean up the fossil fuel CO2, but it 16 00:01:09,980 --> 00:01:15,020 takes a very long time. The other thing you should know is 17 00:01:15,020 --> 00:01:20,890 that there are ways in which the geometry of the geology 18 00:01:20,890 --> 00:01:27,370 can alter the set point of the thermostat. 19 00:01:27,370 --> 00:01:30,990 The thermostat regulates the temperature the way a thermostat of house 20 00:01:30,990 --> 00:01:35,390 can regulate the furnace and the house temperature. 21 00:01:40,430 --> 00:01:45,670 Slowly change the dial on the thermostat by changing the geometry of where 22 00:01:45,670 --> 00:01:51,490 the land and oceans are, mountain building, 23 00:01:51,490 --> 00:01:56,870 and how fast the CO2 is coming out of the Earth by de-gassing and things like that. 24 00:01:56,870 --> 00:02:02,770 Earth has tended to drift back and forth between hothouse climates, 25 00:02:02,770 --> 00:02:06,580 where there's basically no ice on earth at all, 26 00:02:06,580 --> 00:02:11,210 and then climates like today, we call this an ice age climate, even though 27 00:02:13,250 --> 00:02:15,070 it's not as big an ice age as it was, 28 00:02:15,070 --> 00:02:19,020 twenty thousand years ago, the last glacial maximum. 29 00:02:19,020 --> 00:02:23,018 But there still are major ice sheets on earth in Antarctica and in Greenland. 30 00:02:23,018 --> 00:02:28,190 And so geologists would say that we are still in an ice age. 31 00:02:28,190 --> 00:02:30,740 If you go to a natural history museum and 32 00:02:30,740 --> 00:02:34,090 go see the dinosaur dioramas, they always looks very tropical. 33 00:02:34,090 --> 00:02:36,260 That was the dinosaurs existed during a 34 00:02:36,260 --> 00:02:39,410 Hot House period of Earth's climate. 35 00:02:39,410 --> 00:02:43,550 This going back and forth between these two major kinds of climate. 36 00:02:43,550 --> 00:02:48,860 Is, is driven by setting the thermostat, by changing the way that the CO2 37 00:02:48,860 --> 00:02:50,520 is degassing from the earth, or the 38 00:02:50,520 --> 00:02:52,400 way that it's weathering. 39 00:02:53,980 --> 00:02:58,480 Mars is a smaller planet than Venus or Earth 40 00:02:58,480 --> 00:03:01,700 which meant that it cooled down more quickly. 41 00:03:01,700 --> 00:03:04,730 Actually the biggest volcano in the solar system 42 00:03:04,730 --> 00:03:10,120 is on mars, Olympus Mons, it's called. But it's tectonically dead; 43 00:03:10,120 --> 00:03:14,930 the interior of Mars has cooled down enough that it doesn't do this trick 44 00:03:14,930 --> 00:03:19,490 of of metamorphosis, cooking the calcium carbonate, 45 00:03:19,490 --> 00:03:21,820 to push the CO2 out to the atmosphere. 46 00:03:21,820 --> 00:03:28,440 The thermostat is broken on Mars, because it's tectonically dead. 47 00:03:28,440 --> 00:03:30,730 It's broken on Venus because 48 00:03:30,730 --> 00:03:32,120 weathering can't happen. 49 00:03:32,120 --> 00:03:36,053 But on Earth, it's still functioning in a very beautiful way.