2 00:00:09,660 --> 00:00:13,710 The next kind of fossil fuel to consider is oil. 3 00:00:13,710 --> 00:00:17,830 Oil, as you know, is what they make gasoline out of. 4 00:00:17,830 --> 00:00:19,610 It's the most convenient fossil fuel. 5 00:00:19,610 --> 00:00:22,360 It's therefore the most precious, the most expensive. 6 00:00:23,750 --> 00:00:28,050 Oil is formed not from land plants like coal. 7 00:00:28,050 --> 00:00:35,530 But mostly from plankton in the ocean, that land on the bottom of the ocean and 8 00:00:35,530 --> 00:00:40,240 can be preserved in the sediments, if the conditions are right. 9 00:00:40,240 --> 00:00:43,610 Actually, most sediments at the bottom of the ocean don't 10 00:00:43,610 --> 00:00:47,980 have enough organic carbon in them, to really make much oil. 11 00:00:47,980 --> 00:00:53,250 Oil comes from very special what are called oil source rocks. 12 00:00:53,250 --> 00:00:57,600 The entire oil field in the Middle East comes 13 00:00:57,600 --> 00:01:00,480 from source rocks that are just a few feet thick. 14 00:01:00,480 --> 00:01:02,690 Very special rocks, very special conditions 15 00:01:02,690 --> 00:01:06,350 are required to concentrate organic carbon 16 00:01:06,350 --> 00:01:10,850 in the sediments to a high enough degree that you can make oil. 17 00:01:10,850 --> 00:01:14,510 Then, after the carbon is deposited to these source rocks, 18 00:01:14,510 --> 00:01:17,530 it has to be cooked just right to make oil. 19 00:01:17,530 --> 00:01:22,000 There's a depth range in the earth between about 20 00:01:22,000 --> 00:01:25,930 2 and 4 kilometers which is called the oil window. 21 00:01:25,930 --> 00:01:29,890 The temperature gets higher the deeper you get in the earth. 22 00:01:29,890 --> 00:01:32,710 If the source rocks are not buried 23 00:01:32,710 --> 00:01:36,030 to a deep enough level, you'll have immature oil. 24 00:01:36,030 --> 00:01:39,770 Some tar sand, something like that. 25 00:01:39,770 --> 00:01:45,610 Or if it gets buried too deeply out the bottom of the oil window, the carbon 26 00:01:45,610 --> 00:01:51,990 will be converted to natural gas. It's very specific conditions that 27 00:01:51,990 --> 00:01:55,280 allow the formation of liquid oil. 28 00:01:55,280 --> 00:02:02,120 And then to get it out, most of the oil that's extracted Is stuff that has migrated 29 00:02:02,120 --> 00:02:05,060 in the sediment column and found 30 00:02:05,060 --> 00:02:08,140 some trap where it can accumulate. 31 00:02:08,140 --> 00:02:11,260 Probably, most of the oil that was ever formed on Earth 32 00:02:11,260 --> 00:02:14,090 just leaked back to the surface of the Earth and was gone forever. 33 00:02:14,090 --> 00:02:17,150 But some tiny fraction of it gets trapped in these 34 00:02:17,150 --> 00:02:21,570 traps, which are amenable to harvesting. 35 00:02:21,570 --> 00:02:24,430 That's why the inventory of oil on earth 36 00:02:24,430 --> 00:02:26,250 is so much less than the inventory of coal, 37 00:02:26,250 --> 00:02:29,200 because of all of those unlikely things that have to happen, 38 00:02:29,200 --> 00:02:32,380 in order for a carbon molecule to end up as as oil. 39 00:02:33,680 --> 00:02:40,510 Oil has a long chain structures of of carbons. 40 00:02:40,510 --> 00:02:42,910 And each carbon, 41 00:02:42,910 --> 00:02:45,280 because of the number of electrons it has, because of its chemistry, 42 00:02:45,280 --> 00:02:48,960 each carbon has to have four bonds to it. 43 00:02:48,960 --> 00:02:54,750 This is a hexane molecule. These carbons 44 00:02:54,750 --> 00:03:00,400 on the end have to have three hydrogens in order for this carbon here 45 00:03:00,400 --> 00:03:04,140 to have four bonds, or these ones in the middle have 2 hydrogens each, 46 00:03:04,140 --> 00:03:07,390 and then 2 bonds there and there on either side. 47 00:03:08,570 --> 00:03:13,110 If you take the average of the carbon and 48 00:03:13,110 --> 00:03:18,960 hydrogens in this molecule it kind of looks like CH2. 49 00:03:18,960 --> 00:03:24,410 Which means that it's more reduced than coal. 50 00:03:24,410 --> 00:03:28,780 This has an oxidation state of, the hydrogen is 2 51 00:03:28,780 --> 00:03:33,870 times plus 1, and so the carbon is, minus 2. 52 00:03:33,870 --> 00:03:37,380 The oxidation state of carbon in coal is zero. 53 00:03:37,380 --> 00:03:40,180 Here, it's minus two, so it's more reduced than coal. 54 00:03:40,180 --> 00:03:44,280 You get more energy per carbon atom 55 00:03:44,280 --> 00:03:47,730 from oil, than you do from coal. 56 00:03:50,310 --> 00:03:52,830 There are two different ways of thinking 57 00:03:52,830 --> 00:03:57,230 about how long the oil will last. 58 00:03:57,230 --> 00:04:03,870 One method is to take the reserves to production ratio. 59 00:04:03,870 --> 00:04:06,110 The units of that, you've always gotta keep 60 00:04:06,110 --> 00:04:08,220 in track of the units, they will 61 00:04:08,220 --> 00:04:11,900 tell you what's going on, could be gigatons of carbon 62 00:04:11,900 --> 00:04:15,770 for reserves, and then gigatons of carbon per year for 63 00:04:15,770 --> 00:04:18,110 the rate of production. 64 00:04:18,110 --> 00:04:19,920 That's what they in the industry call 65 00:04:19,920 --> 00:04:23,580 extracting oil from the ground is "production". 66 00:04:23,580 --> 00:04:26,910 Cancelling the units we end up with 67 00:04:26,910 --> 00:04:30,780 units of years and this would be 68 00:04:32,840 --> 00:04:36,970 how much time until the last drop is extracted, that 69 00:04:36,970 --> 00:04:41,830 we now know about, at the present day rate of production. 70 00:04:41,830 --> 00:04:46,730 If you look at this plot of the historical evolution of 71 00:04:46,730 --> 00:04:51,040 this ratio through time, what you'll see is that there's 40 years 72 00:04:51,040 --> 00:04:55,170 of oil left. And 40 years ago there was also 40 years 73 00:04:55,170 --> 00:04:58,020 of oil left, and it looks like sort of a perpetual 74 00:04:58,020 --> 00:04:58,780 motion machine. 75 00:04:58,780 --> 00:05:01,080 Like there could be oil forever because if we 76 00:05:01,080 --> 00:05:03,920 could discover it as quickly as its being produced. 77 00:05:04,940 --> 00:05:07,130 Another way to think about oil though, 78 00:05:07,130 --> 00:05:12,930 Is using an idea known as peak oil, and this is based on the 79 00:05:12,930 --> 00:05:19,380 observation that the rate of extracting oil from some oil field. 80 00:05:19,380 --> 00:05:23,940 Like the state of Texas for example tends to follow 81 00:05:23,940 --> 00:05:27,260 what is called a Gaussian, or a bell curve. 82 00:05:27,260 --> 00:05:28,670 This is an empirical relation. 83 00:05:28,670 --> 00:05:30,150 This is an observation. 84 00:05:30,150 --> 00:05:32,940 Gee, it kind of looks like this. It could look different. 85 00:05:32,940 --> 00:05:34,520 The rate of extraction could look different. 86 00:05:34,520 --> 00:05:37,470 But what tends to happen is you have a 87 00:05:37,470 --> 00:05:42,010 ramping up period as the infrastructure is getting put into place. 88 00:05:42,010 --> 00:05:45,240 And then the rate of growth tends to sort of taper off. 89 00:05:45,240 --> 00:05:48,440 And then it starts to come back down. 90 00:05:48,440 --> 00:05:49,030 What this 91 00:05:49,030 --> 00:05:51,570 means is that, the implication of this is that 92 00:05:51,570 --> 00:05:56,680 the peak comes when the oil is only half gone. 93 00:05:56,680 --> 00:06:00,340 As opposed to over here, we were looking at the last drop. 94 00:06:00,340 --> 00:06:03,430 Here, we're thinking about where the peak should be, 95 00:06:03,430 --> 00:06:09,430 and if you have demand that's growing exponentially. 96 00:06:09,430 --> 00:06:14,350 Where the shortage is going to happen is at that peak. 97 00:06:14,350 --> 00:06:19,950 Looking at the amount of oil that is thought to 98 00:06:19,950 --> 00:06:26,130 exist on Earth today and the history of that oil extraction rate so far, 99 00:06:26,130 --> 00:06:28,470 we can use this theory to come up with some 100 00:06:28,470 --> 00:06:32,690 estimate of when the peak rate of oil extraction will be. 101 00:06:32,690 --> 00:06:34,240 And we're right about close to the 102 00:06:34,240 --> 00:06:39,650 peak now. The traditional fossil fuel inventories 103 00:06:39,650 --> 00:06:41,820 of oil are about 200 gigatons. 104 00:06:41,820 --> 00:06:44,710 And we've already extracted about 100 gigatons 105 00:06:44,710 --> 00:06:46,910 of that, so we're about halfway there. 106 00:06:46,910 --> 00:06:49,520 Peak oil would say that this is the 107 00:06:49,520 --> 00:06:53,740 time when oil is going to start getting more scarce.