WEBVTT 00:01.233 --> 00:02.133 RONALD SMITH: I put the word-- 00:02.133 --> 00:03.833 the number seven billion there because 00:03.833 --> 00:06.803 according to what I read in the newspaper, this was the 00:06.800 --> 00:11.900 weekend where the world's population just increased past 00:11.900 --> 00:12.970 seven billion. 00:12.967 --> 00:16.727 So it's kind of an important day in terms of world 00:16.733 --> 00:17.903 population. 00:17.900 --> 00:21.370 I'm going to talk about population a little bit a week 00:21.367 --> 00:24.027 or two from now when we're talking about global warming 00:24.033 --> 00:25.933 issues and environmental issues. 00:25.933 --> 00:32.173 But every scientist who's looked at this issue would 00:32.167 --> 00:39.767 probably define the holding capacity of the planet, in 00:39.767 --> 00:42.227 other words the number of people that could live here 00:42.233 --> 00:44.033 sustainably. 00:44.033 --> 00:46.203 Everyone would define it differently depending on how 00:46.200 --> 00:49.330 they do the calculation. 00:49.333 --> 00:52.073 My guess would be that the holding capacity of the 00:52.067 --> 00:54.967 planet's probably about half that number. 00:54.967 --> 00:58.767 Probably about three or four billion. 00:58.767 --> 01:03.427 Now, I may be way off on that, but by my estimate we've long 01:03.433 --> 01:08.003 since shot past the holding capacity, which means that 01:08.000 --> 01:10.530 we're basically using up resources 01:10.533 --> 01:12.533 that cannot be renewed. 01:15.267 --> 01:19.197 So eventually something will have to adjust either a very 01:19.200 --> 01:22.270 different kind of living or come down to a different 01:22.267 --> 01:24.627 population. 01:24.633 --> 01:29.773 Anyway, it's a troublesome number. 01:29.767 --> 01:30.597 What else? 01:30.600 --> 01:33.170 Ah well we got to experience our first nor'easter. 01:33.167 --> 01:36.797 It was quite exciting. 01:36.800 --> 01:38.670 Of course, one of the remarkable things about these 01:38.667 --> 01:43.127 storms, they come up the coast, but they end up mixing 01:43.133 --> 01:44.873 warm and cold air. 01:44.867 --> 01:48.897 So you get the warm air coming from the south with lots of 01:48.900 --> 01:52.230 water vapor being lifted, producing lots of 01:52.233 --> 01:53.033 precipitation. 01:53.033 --> 01:56.203 And yet the cold air comes down from the north, from the 01:56.200 --> 01:59.730 west side of the storm, wraps around, and allows you to keep 01:59.733 --> 02:04.003 that snow, which was formed aloft by the ice phase 02:04.000 --> 02:06.200 mechanism, allows you to keep it as snow all 02:06.200 --> 02:07.270 the way to the ground. 02:07.267 --> 02:10.897 So even in this time of the season, which is generally not 02:10.900 --> 02:14.730 so cold, we had pretty good snowfalls because the cold air 02:14.733 --> 02:18.503 down from Canada allowed that snow to keep as snow as it 02:18.500 --> 02:20.370 fell all the way to the ground. 02:20.367 --> 02:23.497 The unusual thing about it was it was a little bit earlier 02:23.500 --> 02:26.870 than we typically have nor'easters. 02:26.867 --> 02:30.497 And that combined with the fact that as the last 20 or 30 02:30.500 --> 02:35.170 years have gone by, we've gotten warming in New England, 02:35.167 --> 02:38.297 which has kept the leaves on the trees later 02:38.300 --> 02:39.300 and later in later. 02:39.300 --> 02:45.530 So in my recollection, this was the first real nor'easter 02:45.533 --> 02:47.803 that's come while all of the, or most of the leaves were 02:47.800 --> 02:49.900 still on the trees. 02:49.900 --> 02:53.130 20 years ago, the leaves were off the trees 02:53.133 --> 02:55.373 easily two weeks ago. 02:55.367 --> 02:58.997 Mid-October everything was down, and now we still have 02:59.000 --> 03:01.570 the leaves and now we get our first nor'easter. 03:01.567 --> 03:06.627 So it's a subtle indication, maybe not so subtle, that 03:06.633 --> 03:09.873 things are changing when you can get a nor'easter coming 03:09.867 --> 03:12.167 while the leaves are still on the trees. 03:12.167 --> 03:12.797 Interesting. 03:12.800 --> 03:14.670 Any comments on that? 03:14.667 --> 03:17.597 Anybody get out and try skiing in the snow? 03:17.600 --> 03:18.570 It was very wet, wasn't it? 03:18.567 --> 03:24.967 So more of a sloppy snow than anything else. 03:24.967 --> 03:30.367 Any questions before we get started today? 03:30.367 --> 03:31.997 OK. 03:32.000 --> 03:34.830 Well we had a little bit to finish up on our 03:34.833 --> 03:39.003 discussion of ice. 03:39.000 --> 03:41.470 We hadn't quite finished the mountain glacier section, so 03:41.467 --> 03:43.567 I've gone going back to this first 03:43.567 --> 03:46.997 diagram from that section. 03:47.000 --> 03:49.730 I wanted to remind you about the definition 03:49.733 --> 03:51.873 of a tidewater glacier. 03:51.867 --> 03:57.427 That's when a glacier comes down to the sea so that pieces 03:57.433 --> 04:02.033 can break off and form icebergs. 04:02.033 --> 04:04.373 And some, of course, don't get down that far. 04:06.867 --> 04:08.627 Maybe I'll get the lights off for this. 04:16.567 --> 04:19.967 An interesting set of glaciers is the North and South 04:19.967 --> 04:24.667 Patagonian Icefields down in the Southern Andes. 04:24.667 --> 04:27.197 The North Patagonian Ice Sheet is here, the Southern one is 04:27.200 --> 04:28.900 here, it's larger. 04:28.900 --> 04:33.000 And many of them actually calve off their glaciers in 04:33.000 --> 04:35.930 these big lakes to the east into Argentina. 04:35.933 --> 04:40.233 So if you were to go down there and sign on to a tourist 04:40.233 --> 04:43.873 boat that would take you up to the calving glaciers, they 04:43.867 --> 04:47.397 would be in these lakes for the most part, rather than in 04:47.400 --> 04:50.930 the fjords coming in from the Pacific Ocean. 04:50.933 --> 04:52.703 So that's kind of an interesting place. 04:52.700 --> 04:56.900 But remember, they're calving in fresh water there. 04:56.900 --> 04:58.430 They're not really-so I guess I wouldn't really call them 04:58.433 --> 05:02.603 tidewater glaciers, although you could argue it either way. 05:02.600 --> 05:06.300 They're calving into water, but it's fresh water lakes 05:06.300 --> 05:11.930 rather than seawater with tides. 05:11.933 --> 05:15.803 Flying over it, you get to see these snow-covered mountains, 05:15.800 --> 05:22.800 you get to see some of the ice breaking up into crevasses as 05:22.800 --> 05:24.430 they begin to flow over a bend. 05:24.433 --> 05:27.403 Wherever they've got a drop over a sudden break in the 05:27.400 --> 05:31.200 slope, they often break up into these deep crevasses. 05:31.200 --> 05:34.970 And of course, they're covered with snow, but if you were to 05:34.967 --> 05:40.997 fall into that, you fall down 50 or 100 meters and be lost. 05:41.000 --> 05:45.530 But you can see the flow streaks, these medial moraines 05:45.533 --> 05:48.533 follow it down to where the calving occurs. 05:48.533 --> 05:50.633 It's a bad picture from an aircraft. 05:50.633 --> 05:53.133 There's a lake there and the icebergs are 05:53.133 --> 05:54.373 calving into the lake. 05:57.433 --> 05:58.533 You see it here as well. 05:58.533 --> 06:03.433 You see these various moraines, medial moraines 06:03.433 --> 06:05.873 going down and then they break off into the 06:05.867 --> 06:07.667 little lake down there. 06:10.767 --> 06:16.127 Now, there's been a trend in the amount of ice in mountain 06:16.133 --> 06:19.103 glaciers, and it's negative most places. 06:19.100 --> 06:21.830 This shows a number of different parts around the 06:21.833 --> 06:25.273 world where you've got mountain glaciers, and it's 06:25.267 --> 06:29.797 kept track of their mass since 1960. 06:29.800 --> 06:32.330 The units here are meters of water equivalent. 06:32.333 --> 06:37.303 So it's not how deep the snow or the ice is on the glacier, 06:37.300 --> 06:40.100 but if you were to melt it into liquid how 06:40.100 --> 06:40.700 deep it would be. 06:40.700 --> 06:44.530 That's a convenient reference because snow can be of 06:44.533 --> 06:49.103 different densities, and even compacted snow, depending on 06:49.100 --> 06:51.930 how tight it's been compacted, may not reach the 06:51.933 --> 06:53.273 full density of ice. 06:53.267 --> 06:56.997 So for this kind of mass balance calculation, it's more 06:57.000 --> 07:02.200 convenient to, in the end, describe it as a loss in a 07:02.200 --> 07:05.730 depth of water equivalent. 07:05.733 --> 07:08.173 A little bit hard to follow the colors, but in Patagonia 07:08.167 --> 07:11.627 where I was just pointing, we've had some of the largest 07:11.633 --> 07:17.003 drops, 35 meters of water equivalent, a decrease in the 07:17.000 --> 07:20.230 thickness of those mountain glaciers. 07:20.233 --> 07:21.803 Alaska and the coast mountains have 07:21.800 --> 07:23.500 decreased rapidly as well. 07:23.500 --> 07:28.200 And the Northwestern USA, for example, Glacier National 07:28.200 --> 07:32.170 Park, named after its glaciers, is having one of the 07:32.167 --> 07:36.067 most rapid decreases. 07:36.067 --> 07:39.167 The word there is if you want to see the glaciers in Glacier 07:39.167 --> 07:42.327 National Park you better go there in the next five years 07:42.333 --> 07:46.873 because they're diminishing pretty rapidly. 07:46.867 --> 07:49.467 However, there are some glaciers that are not 07:49.467 --> 07:50.197 changing very much. 07:50.200 --> 07:54.630 For example, in the arctic, and again, I'm not sure of the 07:54.633 --> 07:57.333 color codes here, but it looks like Europe and the Andean 07:57.333 --> 08:02.733 glaciers this would be the Southern Andes, this would be 08:02.733 --> 08:06.433 the rest of the Central Andes they are not changing so 08:06.433 --> 08:10.333 dramatically, at least not until the last few years. 08:10.333 --> 08:15.433 So it's a mixed story, but mostly strongly negative for 08:15.433 --> 08:18.673 the trends on those mountain glaciers. 08:18.667 --> 08:21.397 To wrap-up I wanted to go back and look at Greenland. 08:21.400 --> 08:23.500 We've already talked about it a little bit, but just to 08:23.500 --> 08:25.770 summarize some of the changes that are 08:25.767 --> 08:27.227 occurring in Greenland. 08:27.233 --> 08:31.073 Here are some of the glaciers coming off of the main 08:31.067 --> 08:34.927 Greenland Ice sheet as a function of time from 2000 08:34.933 --> 08:37.703 till almost the present day. 08:37.700 --> 08:39.470 We looked at the Jakobshaven one. 08:39.467 --> 08:43.097 We've spent some time talking about those. 08:43.100 --> 08:45.330 I haven't shown you the other ones. 08:45.333 --> 08:47.633 Oh, I did show you the Petermann up in the 08:47.633 --> 08:49.903 northwestern part. 08:49.900 --> 08:51.570 For the most part these are negative. 08:51.567 --> 08:54.667 Some very strongly negative, some not so strongly. 08:54.667 --> 08:58.867 But generally the glaciers are retreating. 08:58.867 --> 09:01.897 This is in units of square kilometers. 09:01.900 --> 09:04.900 So the base of it, it's not keeping track of thickness 09:04.900 --> 09:07.700 now, but the area as it decreases. 09:07.700 --> 09:10.000 Generally negative. 09:10.000 --> 09:11.670 And we saw Petermann's glacier. 09:11.667 --> 09:17.397 So when that drops off, they decrease the area estimate of 09:17.400 --> 09:18.800 the Petermann glacier. 09:18.800 --> 09:21.330 And some would argue well that's not a significant loss 09:21.333 --> 09:23.603 because that'll refill eventually, but that's how 09:23.600 --> 09:27.000 they've done the calculation. 09:27.000 --> 09:29.200 And then we looked at Jakobshaven before and saw 09:29.200 --> 09:33.730 that its calving front was retreating with time as well, 09:33.733 --> 09:36.973 and that shows up on the time plot also. 09:36.967 --> 09:39.227 Now, there's another thing we can investigate about 09:39.233 --> 09:43.903 Greenland, and that is the amount of surface area up on 09:43.900 --> 09:47.300 the ice sheet that has meltwater in the 09:47.300 --> 09:48.530 middle of the summer. 09:51.033 --> 09:53.733 And what's shown--so you can fly a satellite over, look 09:53.733 --> 09:57.703 down, and by the way light reflects off the ice sheet, 09:57.700 --> 10:02.670 you could determine whether or not the snow is wet whether 10:02.667 --> 10:07.397 it's got meltwater mixed in with the snow. 10:07.400 --> 10:18.730 And in 1992 the pale area was shown to have melt water in 10:18.733 --> 10:19.573 the warm season. 10:19.567 --> 10:23.327 And now, 2005, even this deeper red area. 10:23.333 --> 10:26.503 It's only the diminishing white area that is free of 10:26.500 --> 10:29.770 melt water, and that's an indication that the climate is 10:29.767 --> 10:31.497 changing as well. 10:31.500 --> 10:34.970 What happens to that melt water, some of it just stays 10:34.967 --> 10:36.897 there and refreezes the next winter. 10:36.900 --> 10:42.800 Some of it runs off in this rather remarkable called a 10:42.800 --> 10:47.500 moulin, which is basically a hole that develops in the ice 10:47.500 --> 10:51.430 sheet that allows surface waters that are melting in the 10:51.433 --> 10:56.503 summer to drain and fall a distance of perhaps a 10:56.500 --> 11:00.630 kilometer or so down to the base of the glacier. 11:00.633 --> 11:02.303 And then it'll flow along the base of the 11:02.300 --> 11:05.800 glacier out to the sea. 11:05.800 --> 11:08.000 So this is an example of one of those moulins. 11:08.000 --> 11:11.100 Up on the Greenland ice sheet, water then draining down into 11:11.100 --> 11:14.700 this hole that takes it down to the bottom of the glacier. 11:17.300 --> 11:18.230 Any questions on that? 11:18.233 --> 11:20.103 It's a summertime, of course. 11:23.300 --> 11:27.600 Recently we've got a new technology to keep track of 11:27.600 --> 11:29.800 what's happening to Greenland and other 11:29.800 --> 11:31.030 things around the world. 11:31.033 --> 11:34.573 It's called the GRACE satellite, and maybe you can 11:34.567 --> 11:36.167 make out the acronym here. 11:36.167 --> 11:38.867 Gravity Recovery And Climate Experiment. 11:38.867 --> 11:41.067 That's GRACE. 11:41.067 --> 11:47.197 And it consists of two satellites moving around the 11:47.200 --> 11:52.530 planet very close to each other with a laser beam going 11:52.533 --> 11:57.103 from one to the other doing accurate laser ranging. 11:57.100 --> 12:01.670 So you know within a millimeter or so the distance 12:01.667 --> 12:05.767 between those two satellites as they move. 12:05.767 --> 12:12.067 Well, as the Earth is not uniform in its density, the 12:12.067 --> 12:16.197 continents have mass, other things have mass 12:16.200 --> 12:20.330 concentrations that make the gravity field of the planet a 12:20.333 --> 12:22.533 little bit irregular. 12:22.533 --> 12:25.133 And by sending a satellite around that feels that 12:25.133 --> 12:28.603 gravity, and keeping track of how the distance between the 12:28.600 --> 12:32.700 two satellites varies during the orbit, they can map out 12:32.700 --> 12:36.070 these gravitational anomalies around the 12:36.067 --> 12:37.197 surface of the Earth. 12:37.200 --> 12:40.730 And this is an exaggerated what they've done is take a 12:40.733 --> 12:48.703 globe, and in three dimensions kind of made it nobly so that 12:48.700 --> 12:52.770 it shows you where the higher mass concentrations are. 12:52.767 --> 12:57.467 So this kind of irregular gravity field is what GRACE 12:57.467 --> 12:59.727 can detect as it goes around. 12:59.733 --> 13:02.303 Now that satellit's all that's been in orbit for a few years 13:02.300 --> 13:05.400 now, and one of the applications of it is to look 13:05.400 --> 13:09.170 at not just the gravity concentrations near Greenland, 13:09.167 --> 13:12.067 but how they've been changing in time. 13:12.067 --> 13:14.827 That's what shown in this diagram. 13:14.833 --> 13:18.533 So two plots are shown, one for Southeast Greenland, that 13:18.533 --> 13:20.703 would be this area here. 13:20.700 --> 13:23.830 The other for Northwest Greenland up here. 13:23.833 --> 13:28.573 The time runs from 2002 to 2010, and this is the 13:28.567 --> 13:35.027 centimeter of water equivalent thickness removed from, 13:35.033 --> 13:38.003 ormissing from that part of Greenland over 13:38.000 --> 13:39.400 that period of time. 13:39.400 --> 13:42.970 And for Southeast Greenland, putting a straight line 13:42.967 --> 13:46.167 through there, you get about minus eight centimeters per 13:46.167 --> 13:48.897 year of water equivalent loss. 13:48.900 --> 13:52.230 And for Northwest Greenland it's about minus seven 13:52.233 --> 13:53.203 centimeters per year. 13:53.200 --> 13:55.130 So the two values are roughly consistent. 13:55.133 --> 13:57.903 That tells you that the overall mass of the Greenland 13:57.900 --> 14:00.500 ice sheet is decreasing. 14:00.500 --> 14:02.830 You can do calculations with these numbers and figure out 14:02.833 --> 14:05.703 how long it would take before it would all be lost. It'd be 14:05.700 --> 14:10.800 quite a number of years because these ice layers are 14:10.800 --> 14:12.900 quite thick, a kilometer or more. 14:12.900 --> 14:15.000 But nevertheless, it represents quite 14:15.000 --> 14:16.070 a bit of mass loss. 14:16.067 --> 14:21.127 And when that water melts and goes into the sea, of course, 14:21.133 --> 14:24.833 that raises sea level a little bit. 14:24.833 --> 14:27.633 And that's a calculation you can do as well. 14:27.633 --> 14:31.603 If you know the area of Greenland and how much this is 14:31.600 --> 14:35.270 decreasing per unit time, you can use the surface area of 14:35.267 --> 14:38.797 the oceans to compute how much that is going 14:38.800 --> 14:40.830 to raise sea level. 14:40.833 --> 14:42.073 Any questions on that? 14:45.900 --> 14:49.370 Well that's the end of the story on modern ice, current 14:49.367 --> 14:51.097 ice on the planet. 14:51.100 --> 14:54.130 We could take a few minutes if there are any questions about 14:54.133 --> 14:57.273 any of the things that I've covered with regards to ice in 14:57.267 --> 14:58.497 the climate system. 15:00.867 --> 15:01.597 Anything? 15:01.600 --> 15:02.130 Yeah, Julia. 15:02.133 --> 15:03.403 Student: So glaciers are always 15:03.400 --> 15:06.100 associated with mountains? 15:06.100 --> 15:06.700 PROFESSOR: That's right. 15:06.700 --> 15:11.700 I would say the word glacier usually implies moving ice. 15:11.700 --> 15:13.230 Moving gravitationally. 15:13.233 --> 15:18.773 So if you've got an ice sheet like Greenland, and through 15:18.767 --> 15:23.697 the gaps, like here and here, where the ice can squeeze out 15:23.700 --> 15:26.700 and come down to sea level, that would be a glacier. 15:26.700 --> 15:29.470 You wouldn't refer to this as a glacier. 15:29.467 --> 15:30.927 This is an ice sheet. 15:30.933 --> 15:33.603 But where it's squeezing and flowing down to sea level, 15:33.600 --> 15:34.430 that would be a glacier. 15:34.433 --> 15:38.273 Or if you have a mountain glacier, a small mountain 15:38.267 --> 15:41.397 glacier with sliding gravitationally, that would be 15:41.400 --> 15:42.630 a glacier as well. 15:42.633 --> 15:47.103 So just don't use it with respect to a large ice sheet 15:47.100 --> 15:51.530 and you'll be safe on the terminology side of things. 15:51.533 --> 15:52.803 Other questions on this? 15:57.900 --> 16:06.400 Well we're going to shift gears a little bit. 16:33.367 --> 16:36.267 We're going to talk about how climate has been 16:36.267 --> 16:40.027 changing with time. 16:40.033 --> 16:41.303 And for this you should be reading 16:41.300 --> 16:44.230 Chapter 13 in your book. 16:44.233 --> 16:47.033 The author of the textbook has done a good job with 13. 16:47.033 --> 16:50.303 He's made a little different set of choices than I've made 16:50.300 --> 16:52.130 about what to emphasize. 16:52.133 --> 16:56.333 But I think the combination of the two, Chapter 13 in Ahrens, 16:56.333 --> 16:59.633 and my presentation here today, and this'll spill over 16:59.633 --> 17:04.273 into Wednesday, will give you a good introduction to how the 17:04.267 --> 17:07.967 climate is changing on the Earth. 17:07.967 --> 17:10.027 I've made a decision to focus on the last 17:10.033 --> 17:13.333 five million years. 17:13.333 --> 17:14.903 And the reason for that well there are really 17:14.900 --> 17:15.870 three reasons for that. 17:15.867 --> 17:20.827 One is the continents have pretty much been in their 17:20.833 --> 17:24.533 present position for the last five million years. 17:24.533 --> 17:26.933 So we don't have to worry about the 17:26.933 --> 17:28.373 continents moving around. 17:31.267 --> 17:34.397 Second of all, this has been the period of time in our 17:34.400 --> 17:39.500 planet when humans have been evolving to our current form. 17:39.500 --> 17:45.830 So it's not so distant in the past that we're not engaged in 17:45.833 --> 17:47.703 it as a species. 17:47.700 --> 17:52.970 This is a period of time when we have been coming on to, 17:52.967 --> 17:55.027 evolving to our present form. 17:55.033 --> 18:00.933 And I guess third, we're looking for a period of 18:00.933 --> 18:04.303 geologic history where there's been significant change in 18:04.300 --> 18:07.800 climate in order to make the subject interesting. 18:07.800 --> 18:12.730 But also, one of the reasons for studying past climates is 18:12.733 --> 18:17.873 to provide a context for future climate change. 18:17.867 --> 18:20.927 And to provide a good context for future climate change, you 18:20.933 --> 18:23.303 would like to look at a period of Earth history that had 18:23.300 --> 18:25.500 significant climate change. 18:25.500 --> 18:29.530 And we certainly have it over the last five million years. 18:29.533 --> 18:33.103 So that's the reason why I've decided to focus just on the 18:33.100 --> 18:35.700 last five million years. 18:35.700 --> 18:39.070 There's a number of subcategories or subjects I'm 18:39.067 --> 18:41.727 going to be treating today and tomorrow. 18:41.733 --> 18:46.303 Today we'll probably only get through maybe the first two or 18:46.300 --> 18:49.030 three of these. 18:49.033 --> 18:53.203 We're going to start with a brief overview of the climate 18:53.200 --> 18:57.070 of the last five million years. 18:57.067 --> 18:57.767 How many of you--remind me, how many have 18:57.767 --> 19:01.197 had a geology course? 19:01.200 --> 19:02.570 Just a few of you. 19:02.567 --> 19:05.197 So you know something about this time scale, and I've 19:05.200 --> 19:07.970 mentioned it once or twice before as well. 19:07.967 --> 19:11.067 This is the geologic time scale. 19:11.067 --> 19:15.867 The Earth is something like five or six billion years old. 19:15.867 --> 19:17.797 This goes almost back to that level. 19:17.800 --> 19:23.700 The Precambrian is where we didn't have life in the form 19:23.700 --> 19:26.200 that would leave a fossil record. 19:26.200 --> 19:29.270 Nothing with bones or shells or anything like that. 19:29.267 --> 19:32.727 There was life there, and there's certain types of 19:32.733 --> 19:35.733 physical fossils that are left, but not the actual 19:35.733 --> 19:37.503 remains of the organisms. 19:37.500 --> 19:40.770 Then you go through a series of rapid evolution as you come 19:40.767 --> 19:43.097 up through to the present time. 19:43.100 --> 19:44.870 We're not going to talk about dinosaurs. 19:44.867 --> 19:47.127 The dinosaurs died out right about there. 19:49.700 --> 19:54.970 Probably with an impact from a large meteorite. 19:54.967 --> 19:56.697 Instead we're going to focus just on 19:56.700 --> 19:58.100 these last three periods. 19:58.100 --> 20:03.070 The Pliocene, the Pleistocene, and Holocene, taking us from 20:03.067 --> 20:05.997 approximately five million years up to the present. 20:08.867 --> 20:12.997 I showed you this plate tectonics diagram once before, 20:13.000 --> 20:17.570 coming up in time newer, newer, newer, and newer. 20:17.567 --> 20:20.827 This takes us to the Cretaceous, which is here, 65 20:20.833 --> 20:22.133 million years ago. 20:22.133 --> 20:25.673 We're jumping up now factor of 10 younger than that. 20:25.667 --> 20:28.327 So pretty much the continents are going to be in their 20:28.333 --> 20:32.503 current state for this last five million years. 20:32.500 --> 20:34.930 So we don't have to worry about any of this. 20:34.933 --> 20:38.233 If a continent has a record of a different climate, it's not 20:38.233 --> 20:41.133 because it was at a different latitude. 20:41.133 --> 20:44.603 It's because the climate was actually different on Earth at 20:44.600 --> 20:47.800 that time, not just the continents sliding around 20:47.800 --> 20:49.070 under the climate zones. 20:51.533 --> 20:54.133 Questions there? 20:54.133 --> 20:54.573 All right. 20:54.567 --> 21:00.397 So just a few words about these three periods. 21:00.400 --> 21:06.670 The mid-Pliocene, 3.3 to three million years before present, 21:06.667 --> 21:10.897 similar common locations today, but a significantly 21:10.900 --> 21:14.570 higher global temperature, maybe two to three degrees 21:14.567 --> 21:18.297 Celsius for the average global temperature. 21:18.300 --> 21:21.070 Much more remarkable than that, though, was that the 21:21.067 --> 21:25.697 high latitudes were much warmer than they are today. 21:30.733 --> 21:33.603 There was a little bit of ice on Greenland, but 21:33.600 --> 21:34.930 not a real ice sheet. 21:37.900 --> 21:42.500 Because of that lack of ice, sea level was about 25 meters 21:42.500 --> 21:46.500 higher than it is today. 21:46.500 --> 21:52.070 And for these reasons, there is quite a flurry of research 21:52.067 --> 21:56.197 going on right now about the Pliocene, because it's a 21:56.200 --> 22:00.470 possible analog for what the Earth will be like about 100 22:00.467 --> 22:04.527 years from now with global warming. 22:04.533 --> 22:06.133 I'm going to talk about global warming next week. 22:06.133 --> 22:10.233 But this has really excited a lot of interest, this idea 22:10.233 --> 22:15.103 that maybe there was a period in the past we could look at 22:15.100 --> 22:17.670 to see our future in a sense. 22:17.667 --> 22:22.067 Now whether that turns out to be an accurate analog, I would 22:22.067 --> 22:24.627 say remains to be seen. 22:24.633 --> 22:26.903 But that's one of the reasons why there's so much current 22:26.900 --> 22:30.470 activity about the Pliocene. 22:30.467 --> 22:30.797 Yes? 22:30.800 --> 22:33.100 Student: [INAUDIBLE] 22:33.100 --> 22:36.870 PROFESSOR: So a million years before present. 22:36.867 --> 22:38.567 A million years before present. 22:46.233 --> 22:48.773 These are some of the mammals we had in the Pliocene era. 22:51.300 --> 22:56.130 Saber-toothed tiger and the woolly mammoth. 22:56.133 --> 22:57.433 As I say, no dinosaurs. 22:57.433 --> 23:01.103 That was 60 million years ago. 23:01.100 --> 23:03.430 The Pliocene vegetation now, there's no legend on this 23:03.433 --> 23:08.103 diagram, but the author wanted to make the point that the 23:08.100 --> 23:11.470 normal forests that we have here at mid-latitudes, at that 23:11.467 --> 23:14.797 time extended all the way up into the Canadian archipelago 23:14.800 --> 23:16.170 up into Alaska. 23:16.167 --> 23:21.627 Areas that are now tundra had forests very much like the 23:21.633 --> 23:24.833 ones we have here in Connecticut. 23:24.833 --> 23:27.703 So it really was a period of time when temperatures were 23:27.700 --> 23:32.570 much warmer at the higher latitudes than they are today. 23:36.400 --> 23:42.030 Then we'll jump to the Pleistocene, which is 2.6 23:42.033 --> 23:49.573 million years ago up to just 12,000 years ago. 23:49.567 --> 23:51.797 One of the problems with Paleoclimatology is we've got 23:51.800 --> 23:54.900 to deal with these vast stretches of time. 23:54.900 --> 23:58.630 It's a little bit hard sometimes to conceive of how 23:58.633 --> 24:03.303 long ago that was and how recent this was. 24:03.300 --> 24:06.530 But we'll be working on that today and next time trying to 24:06.533 --> 24:09.803 give you all a better understanding on how these 24:09.800 --> 24:12.400 time scales work. 24:12.400 --> 24:16.430 The Pleistocene was possibly the coldest period in Earth 24:16.433 --> 24:21.303 history, although there have been discussions of periods of 24:21.300 --> 24:25.830 time hundreds of millions of years ago that 24:25.833 --> 24:26.873 may have been colder. 24:26.867 --> 24:31.167 But at least in recent Earth history, in the last, say, 100 24:31.167 --> 24:35.467 million years or even 200 million years, probably this 24:35.467 --> 24:41.027 was the coldest period in that part of Earth history. 24:41.033 --> 24:44.873 As we'll see, there were lower carbon dioxide concentrations 24:44.867 --> 24:48.397 in the atmosphere than there are today. 24:48.400 --> 24:53.000 And throughout this two and a half million year period, 24:53.000 --> 24:56.530 there were periodic advances and retreats of ice sheets and 24:56.533 --> 24:58.203 mountain glaciers. 24:58.200 --> 25:05.500 So it wasn't a single ice age, in a sense it was a large 25:05.500 --> 25:09.470 number of ice ages with warm-- 25:09.467 --> 25:13.097 brief warm spells in between. 25:13.100 --> 25:17.270 If you averaged, however, it certainly was a very cold 25:17.267 --> 25:18.567 period of time. 25:18.567 --> 25:22.197 Surprising, because we just came out of the Pliocene, 25:22.200 --> 25:24.900 which was warmer than it is today. 25:24.900 --> 25:26.900 Then we go into the Pleistocene, which was much 25:26.900 --> 25:29.730 colder, and then we're going to bounce back out and talk 25:29.733 --> 25:31.433 about modern climate. 25:34.100 --> 25:37.330 I've written here Milankovitch pacing because the advance and 25:37.333 --> 25:43.333 retreat of these ice sheets seems to have been controlled 25:43.333 --> 25:47.433 by slight adjustments in the Earth's orbital parameters. 25:47.433 --> 25:51.473 The so-called Milankovitch theory of climate change, and 25:51.467 --> 25:54.467 I'll talk about that. 25:54.467 --> 25:58.027 And this period of time, 2.6 to the present, includes most 25:58.033 --> 26:05.203 of human evolution, at least the species that have homo in 26:05.200 --> 26:07.600 front of them, as I'll show you in just a minute. 26:07.600 --> 26:11.730 And the Last Glacial Maximum, the last of these ice sheet 26:11.733 --> 26:17.603 advances, was about 14,000 years before present. 26:17.600 --> 26:20.700 And it was just after that that I'll take the official 26:20.700 --> 26:25.230 end of the Pleistocene period. 26:25.233 --> 26:29.173 So I'm kind of defining the end of it as being the end of 26:29.167 --> 26:31.567 the last glacial advance. 26:35.433 --> 26:39.033 Here is a diagram showing human evolution. 26:39.033 --> 26:42.303 There's a time scale up there in millions of years ago. 26:42.300 --> 26:45.070 So here is today, one million, two million, three 26:45.067 --> 26:47.467 million years ago. 26:47.467 --> 26:54.397 The prefix A, Australopithecus is on these brown species 26:54.400 --> 26:55.370 indicators. 26:55.367 --> 26:59.027 And then you get to the homo prefix, and that really takes 26:59.033 --> 27:01.403 you from two million years up to the present. 27:01.400 --> 27:06.130 Homosapiens, however, are only in the last couple of hundred 27:06.133 --> 27:07.903 thousand years. 27:07.900 --> 27:14.030 So climatologically then, the Pleistocene goes from about 27:14.033 --> 27:22.973 here to about there, getting a little bit of Homosapiens in 27:22.967 --> 27:29.997 it, and most of the other ancestors of modern man. 27:30.000 --> 27:33.330 So be sure you have some understanding of this when 27:33.333 --> 27:36.173 we're thinking about paleoclimate so you can make 27:36.167 --> 27:39.827 the necessary connections between human evolution and 27:39.833 --> 27:41.933 the change in climate. 27:41.933 --> 27:43.173 Any questions on that? 27:46.000 --> 27:48.600 If there's any anthropology majors or people who have had 27:48.600 --> 27:52.430 an anthropology course, keep me honest on these things. 27:52.433 --> 27:57.373 I'm not much of an expert on human evolution, but don't 27:57.367 --> 27:59.727 feel afraid to speak out if I say 27:59.733 --> 28:01.103 something wrong about that. 28:03.733 --> 28:06.803 I'm going to come back to this diagram later on, but it suits 28:06.800 --> 28:09.070 the present purpose as well. 28:09.067 --> 28:14.797 It happens to be data from a Vostok ice core, and I will 28:14.800 --> 28:20.630 describe later how this data is gathered and interpreted. 28:20.633 --> 28:24.103 But for the time being let's take it at face value. 28:24.100 --> 28:28.500 Here's a plot of temperature change from present, from the 28:28.500 --> 28:34.170 present day back to 400,000 years ago. 28:34.167 --> 28:40.497 So here is today, and of course by definition, present 28:40.500 --> 28:42.730 change--temperature change from present, that's right 28:42.733 --> 28:46.473 about zero, because here's the present day. 28:46.467 --> 28:50.167 About 10,000 years ago and earlier, we were in a much 28:50.167 --> 28:51.727 colder period of time. 28:51.733 --> 28:54.873 That's the last glacial period. 28:54.867 --> 28:57.997 Then there was another brief interglacial period, about 28:58.000 --> 28:59.930 130,000 years ago. 28:59.933 --> 29:03.373 Then a long glacial period, another brief 29:03.367 --> 29:05.627 interglacial, and so on. 29:05.633 --> 29:10.003 So when I talk about the Pleistocene as being a period 29:10.000 --> 29:14.730 of ice advances and retreats and significant climate 29:14.733 --> 29:16.803 change, this is what I'm talking about. 29:16.800 --> 29:19.930 On average it was much colder than the present day. 29:19.933 --> 29:25.403 Typically four or five or six degrees Celsius colder than 29:25.400 --> 29:26.000 the present day. 29:26.000 --> 29:28.770 But there were other interglacials. 29:28.767 --> 29:31.927 There are other brief periods of warmth. 29:31.933 --> 29:36.403 We're in one today, and about every 100,000, 125,000 29:36.400 --> 29:39.700 thousand years back through this record, there was another 29:39.700 --> 29:42.670 brief interglacial. 29:42.667 --> 29:44.697 That will give you a sense for what I mean by this great 29:44.700 --> 29:48.930 variability that occurred within the Pleistocene period. 29:52.600 --> 29:55.930 At the Last Glacial Maximum, in other words, right about 29:55.933 --> 30:00.603 here, about 20,000 years ago, although you could take it a 30:00.600 --> 30:06.270 little more recent than that, LGM, is the abbreviation for 30:06.267 --> 30:09.697 Last Glacial Maximum, this was the distribution of 30:09.700 --> 30:12.170 continental ice sheets. 30:12.167 --> 30:14.997 It doesn't show Antarctica, but Antarctica still had its 30:15.000 --> 30:18.970 full ice sheet at that time, and Greenland. 30:18.967 --> 30:22.997 But now look, in addition, you've got an even larger ice 30:23.000 --> 30:24.930 sheet over North America called the 30:24.933 --> 30:27.833 Laurentide ice sheet. 30:27.833 --> 30:30.973 And then a large one up over Scandinavia and Northern 30:30.967 --> 30:32.427 Russia as well. 30:32.433 --> 30:39.373 So the number, or the aerial extent of large continental 30:39.367 --> 30:45.167 ice sheets was much larger 14,000, 15,000, 20,000 years 30:45.167 --> 30:48.167 ago than it is today at the end of the 30:48.167 --> 30:51.297 Last Glacial Maximum. 30:51.300 --> 30:53.030 So really a dramatically different climate 30:53.033 --> 30:55.233 then we have today. 30:55.233 --> 30:57.673 This has been one of the biggest paradigm shifts in the 30:57.667 --> 31:02.327 Earth sciences in the last 200 years was to convince 31:02.333 --> 31:04.833 ourselves, other scientists, and finally the general 31:04.833 --> 31:09.233 public, that this recent period was so different 31:09.233 --> 31:11.673 climatologically than the one today. 31:11.667 --> 31:14.367 If you go back and read the scientific literature from the 31:14.367 --> 31:18.897 period 1900, 1910, 1920, there were violent arguments in the 31:18.900 --> 31:21.230 scientific literature about whether this could really be 31:21.233 --> 31:25.103 true, that this short time ago there could have been massive 31:25.100 --> 31:27.200 ice sheets over the continents. 31:27.200 --> 31:28.800 Now we're certain it's true. 31:28.800 --> 31:31.970 We have many, many lines of evidence that convinced us of 31:31.967 --> 31:37.267 that, but it was quite a big deal at the time. 31:37.267 --> 31:40.697 Then the third geologic period that I want you to be familiar 31:40.700 --> 31:43.100 with is the Holocene. 31:43.100 --> 31:46.300 This is defined as a period from 12,000 years before 31:46.300 --> 31:49.470 present to the present day. 31:51.933 --> 31:54.373 It is a current interglacial period. 31:54.367 --> 31:59.567 In other words, the current non-glacial period. 31:59.567 --> 32:02.627 It has modern humans, so development of agriculture, a 32:02.633 --> 32:07.173 nearly constant climate, and nearly steady sea level during 32:07.167 --> 32:08.767 that period of time. 32:08.767 --> 32:13.797 So if you're looking for a reference point from which to 32:13.800 --> 32:18.630 consider or compute climate change, this 32:18.633 --> 32:20.873 is a possible candidate. 32:20.867 --> 32:24.897 Now, it's only 12,000 years, but still, that's quite a 32:24.900 --> 32:25.630 large time. 32:25.633 --> 32:29.103 And for some purposes, that might be a good reference 32:29.100 --> 32:34.000 point for defining climate change. 32:34.000 --> 32:36.930 But be careful, not everyone will agree with you on that. 32:36.933 --> 32:39.873 Some people might say no, you want to, perhaps, go back a 32:39.867 --> 32:43.397 much longer period of time and integrate over all of those 32:43.400 --> 32:47.000 fluctuations in the Pleistocene, or maybe even 32:47.000 --> 32:49.500 include part of the Pliocene in your 32:49.500 --> 32:51.230 definition of a normal climate. 32:51.233 --> 32:56.603 This will haunt us, this idea of what would be the usual or 32:56.600 --> 32:57.730 the normal climate. 32:57.733 --> 33:00.933 It's almost an unanswerable question. 33:00.933 --> 33:05.003 Climate has changed so dramatically over geologic 33:05.000 --> 33:07.800 history that it's real hard to find the time that you could 33:07.800 --> 33:08.870 consider normal. 33:08.867 --> 33:14.067 This might be the best chance for that. 33:14.067 --> 33:15.297 Questions there? 33:17.767 --> 33:21.567 OK so there we have the Pliocene, the Pleistocene, and 33:21.567 --> 33:25.827 the Holocene, at least a brief introduction to those. 33:25.833 --> 33:29.233 Oh, here's a plot of the Holocene temperatures. 33:29.233 --> 33:31.673 This is thousands of years before present, so this goes 33:31.667 --> 33:34.727 back to 12,000 years, which is the beginning of the Holocene. 33:37.600 --> 33:39.130 Temperature--there's a lot of different proxies that are 33:39.133 --> 33:43.103 considered here, and they all give somewhat different 33:43.100 --> 33:45.770 interpretations of past climates. 33:45.767 --> 33:48.367 But if we take a look at the thick black curve, which is 33:48.367 --> 33:51.397 the average of all of the different proxies, here we are 33:51.400 --> 33:55.430 coming out of the last ice age, reaching a value about 33:55.433 --> 33:58.533 10,000 years ago, which remains roughly constant till 33:58.533 --> 34:00.603 the present day. 34:00.600 --> 34:03.170 However, these fluctuations have excited a lot of 34:03.167 --> 34:04.267 discussion. 34:04.267 --> 34:07.227 For example, this slightly warmer period here is often 34:07.233 --> 34:11.603 referred to as the Climatic Optimum between about 8,000 34:11.600 --> 34:15.430 and 5,000 years ago. 34:15.433 --> 34:19.633 So some would argue when I say that the the Holocene climate 34:19.633 --> 34:20.703 was constant. 34:20.700 --> 34:22.730 It wasn't exactly constant. 34:22.733 --> 34:25.033 There were some fluctuations within it. 34:30.100 --> 34:34.330 So that's step one, getting those three time periods out 34:34.333 --> 34:35.633 on the table. 34:35.633 --> 34:37.933 There's lots of paleoclimate methods. 34:37.933 --> 34:40.303 We're not going to have time to talk about these. 34:40.300 --> 34:42.000 But I want to spend the rest of the period today talking 34:42.000 --> 34:43.670 about geomorphology. 34:43.667 --> 34:47.527 That is looking at the landscape 34:47.533 --> 34:50.733 to deduce past climates. 34:50.733 --> 34:52.533 In a way this is the most fun because 34:52.533 --> 34:54.173 we can do it ourselves. 34:54.167 --> 34:57.067 As we drive around the country, look out the car 34:57.067 --> 35:02.597 window, we can begin to see these landscape features that 35:02.600 --> 35:06.100 can be interpreted as evidence of climate change. 35:06.100 --> 35:08.570 So I want to spend quite a bit of time on this because it's 35:08.567 --> 35:10.527 the one that we can really have fun 35:10.533 --> 35:13.133 with and do it ourselves. 35:13.133 --> 35:15.903 I'm going to focus on surface evidence of the Pleistocene 35:15.900 --> 35:19.830 ice ages, and look particularly at these five 35:19.833 --> 35:21.073 geomorphologic features. 35:23.700 --> 35:30.970 A terminal moraine is that pile of debris that marks the 35:30.967 --> 35:33.367 end of a glacier. 35:33.367 --> 35:37.327 Remember, a glacier is moving, carrying material along 35:37.333 --> 35:41.033 underneath it, melting at the front. 35:41.033 --> 35:43.603 So it's like a conveyor belt. 35:43.600 --> 35:47.900 It's bringing material and then the glacier leaves, but 35:47.900 --> 35:50.330 the material piles up. 35:50.333 --> 35:57.333 So if a glacier has a fixed terminus for a number of 35:57.333 --> 36:04.103 decades, it will build up a pile of rubble, rock, and soil 36:04.100 --> 36:05.130 at the end of it. 36:05.133 --> 36:10.573 And then if that glacier were to retreat, you'd have no 36:10.567 --> 36:14.227 glacier here, but you would have that terminal moraine 36:14.233 --> 36:18.403 left as a marker, as evidence of where that glacier was. 36:18.400 --> 36:20.270 So that's the importance of the terminal moraine. 36:20.267 --> 36:24.967 It shows you where the previous end of a glacier was, 36:24.967 --> 36:27.897 if it was there at least for several decades or a few 36:27.900 --> 36:30.600 hundred years. 36:30.600 --> 36:32.970 Here's one, here's a mountain glacier coming down into a 36:32.967 --> 36:38.197 lake, and here at the other end is the terminal moraine. 36:38.200 --> 36:43.270 So at an earlier time, this glacier filled in the lake and 36:43.267 --> 36:45.797 ended right there, and the debris it was carrying 36:45.800 --> 36:49.870 underneath it piled up to form that moraine. 36:49.867 --> 36:53.227 So we see it today, we can say ah, that glacier has retreated 36:53.233 --> 36:57.133 because it's snout used to be right there at that location. 36:57.133 --> 36:59.803 That's the beauty of the terminal moraine. 36:59.800 --> 37:04.100 It gives you this recent history of how far the glacier 37:04.100 --> 37:05.370 had extended. 37:07.267 --> 37:10.627 For scale, here's a fellow standing on top of a pile of 37:10.633 --> 37:13.503 rubber--of rubble, rather. 37:13.500 --> 37:15.400 The glacier's nowhere to be seen, it's 37:15.400 --> 37:16.770 retreated up the valley. 37:16.767 --> 37:22.897 But this is where the snout of that the glacier was. 37:22.900 --> 37:25.430 Now, there's some other things that happens underneath a 37:25.433 --> 37:28.833 large ice sheet that get revealed when the ice finally 37:28.833 --> 37:30.403 melts and moves back. 37:30.400 --> 37:33.170 Well, OK, I've said it wrong, didn't I? 37:33.167 --> 37:34.897 Moved back. 37:34.900 --> 37:39.030 A glacier never moves back. 37:39.033 --> 37:45.803 It's terminus may retreat, but the glacier, the ice itself, 37:45.800 --> 37:50.100 is either stationary or is moving forward. 37:50.100 --> 37:53.570 When you go into a warm period and the glaciers retreat, they 37:53.567 --> 37:57.527 never do it by sliding that glacier back up the valley. 37:57.533 --> 37:59.233 Be very clear on that. 37:59.233 --> 38:03.633 It's only that the apparent end of it may 38:03.633 --> 38:04.873 seem to move back. 38:04.867 --> 38:08.327 But the ice will continue to be flowing from left to right 38:08.333 --> 38:13.403 here as the terminus moves from right to left. 38:13.400 --> 38:17.500 So be very careful about your terminology on this. 38:17.500 --> 38:20.130 Here's a terminal moraine left behind by that. 38:20.133 --> 38:23.273 There's an esker, that I'll define in just a moment, and 38:23.267 --> 38:29.497 there are some drumlins that I will define in just a moment. 38:29.500 --> 38:35.400 An esker is a river flowing underneath the ice, underneath 38:35.400 --> 38:41.470 the ice sheet, that gets partly filled up with debris. 38:41.467 --> 38:44.867 And then when the ice sheet melts, you're left with this 38:44.867 --> 38:49.627 little pile of debris where the river was. 38:49.633 --> 38:53.403 So the river, instead of being a depression in this case as 38:53.400 --> 38:56.730 we're used to seeing, because there was a river up inside a 38:56.733 --> 39:02.173 glacier, actually leaves an elevated tongue marking where 39:02.167 --> 39:05.097 that river was. 39:05.100 --> 39:11.230 Here's a nice example of one up in Manitoba of an esker. 39:11.233 --> 39:14.933 So an ice sheet covered this, there was a river underneath 39:14.933 --> 39:20.273 the ice, and the debris that collected in that sub-ice 39:20.267 --> 39:24.167 river, then when the ice melted away left 39:24.167 --> 39:25.427 you with that esker. 39:28.700 --> 39:33.500 Glacial striations, you can see them here in New England, 39:33.500 --> 39:40.900 scrapes on bedrock indicating that a glacier has slid over 39:40.900 --> 39:42.100 that particular part of rock. 39:42.100 --> 39:45.000 Usually underneath the ice there are chunks of rock 39:45.000 --> 39:46.800 embedded in the ice. 39:46.800 --> 39:49.670 And so you're scraping these embedded chunks over the 39:49.667 --> 39:54.767 bedrock, leaving a scraping mark. 39:54.767 --> 39:58.197 You can tell what direction the glacier was moving. 39:58.200 --> 40:03.630 Well it's hard to distinguish that from that, but at least 40:03.633 --> 40:05.803 you know it was either moving in that direction or in that 40:05.800 --> 40:09.270 direction from the direction of those glacial striations. 40:12.167 --> 40:16.527 Sometimes they can be deeper grooves, as you see in this 40:16.533 --> 40:18.133 piece of rock here. 40:18.133 --> 40:19.573 So that tells you that a glacier has 40:19.567 --> 40:24.167 scraped over this terrain. 40:24.167 --> 40:26.697 The glacial erratic are easy to spot. 40:26.700 --> 40:31.000 A very large boulder sitting on a bedrock that doesn't 40:31.000 --> 40:33.870 match it in terms of rock type. 40:33.867 --> 40:34.767 So it's foreign. 40:34.767 --> 40:35.997 It didn't come from here. 40:36.000 --> 40:39.400 It's been moved from some other place. 40:39.400 --> 40:42.770 Now, if it was a small rock, you could say well maybe water 40:42.767 --> 40:45.027 could have moved that. 40:45.033 --> 40:47.033 But if it gets to be this size there's nothing there for 40:47.033 --> 40:50.433 scale, but that's two or three meters in height water could 40:50.433 --> 40:52.833 not have moved that large rock. 40:52.833 --> 40:55.703 So that had to be a glacier that moved it. 40:55.700 --> 41:01.170 The word erratic means it's a large boulder in a place that 41:01.167 --> 41:04.927 has different rock type than the boulder itself. 41:04.933 --> 41:07.103 So it didn't come from there, it was carried in 41:07.100 --> 41:08.570 by somewhere else. 41:08.567 --> 41:10.897 Sometimes you can trace these back and find out 41:10.900 --> 41:12.500 where they came from. 41:12.500 --> 41:16.000 That will give you a direction of ice motion. 41:16.000 --> 41:21.300 Here's another in Denali National Park and in Calgary, 41:21.300 --> 41:22.870 examples of glacial erratics. 41:22.867 --> 41:27.097 You can spot these pretty easily up in Canada. 41:27.100 --> 41:34.630 A drumlin is a hill that has been shaped by a glacier 41:34.633 --> 41:35.903 sliding over it. 41:38.100 --> 41:43.300 It's got usually a steep end, and a less steep end, 41:43.300 --> 41:45.230 indicating the ice flow, in this case, goes 41:45.233 --> 41:47.903 from left to right. 41:47.900 --> 41:52.100 So it scrapes off material here, and then deposits it on 41:52.100 --> 41:53.800 this long tail back here. 41:56.767 --> 42:01.167 Here's a drumlin seen from the air. 42:01.167 --> 42:03.067 So the glacier was flowing from left to 42:03.067 --> 42:04.297 right in this case. 42:09.600 --> 42:13.330 Here's a bunch of them, I guess the farmers had planted 42:13.333 --> 42:16.433 fields in the flat terrain, but they've left forests on 42:16.433 --> 42:17.703 some of these drumlins. 42:21.400 --> 42:23.870 And then here's a field of drumlins up in Canada seen 42:23.867 --> 42:26.567 from a satellite. 42:26.567 --> 42:29.697 And it's pretty easy to guess which way the ice flow was. 42:29.700 --> 42:33.330 It was from upper left to lower right forming all of 42:33.333 --> 42:34.603 those drumlins. 42:38.667 --> 42:44.097 So that's a little bit of what you can look for as you drive 42:44.100 --> 42:48.730 around to convince yourselves that there was big ice on the 42:48.733 --> 42:50.603 landscape not too long ago. 42:50.600 --> 42:51.370 And this is what it looked like. 42:51.367 --> 42:54.067 So I want to spend a few slides just describing what 42:54.067 --> 42:57.727 the Earth was like during this Last Glacial Maximum. 42:57.733 --> 43:02.833 Roughly 20,000 to 14,000 years before present. 43:02.833 --> 43:06.073 In addition to Greenland and Antarctica, there was this 43:06.067 --> 43:08.467 giant Laurentide ice sheet. 43:08.467 --> 43:10.027 An ice sheet on the West Coast called the 43:10.033 --> 43:11.603 Cordilleran ice sheet. 43:11.600 --> 43:14.700 But look, Alaska was, at least Northern Alaska was 43:14.700 --> 43:16.100 still free of ice. 43:16.100 --> 43:19.300 That's a bit of a surprise. 43:19.300 --> 43:21.930 However, there are also large ice sheets in Scandinavia and 43:21.933 --> 43:23.833 Northern Russia as well. 43:27.367 --> 43:32.067 When you look at the drumlins and the glacial striations, 43:32.067 --> 43:36.867 and the glacial erratics for the Laurentide ice sheet, you 43:36.867 --> 43:40.497 can work out a sense of motion, how the ice was 43:40.500 --> 43:43.530 moving, and this is what you come up with. 43:43.533 --> 43:46.973 The little arrows indicate what local evidence tells us 43:46.967 --> 43:50.197 about the direction of motion of the ice sheet. 43:50.200 --> 43:52.830 Down in our part of the country, it was 43:52.833 --> 43:55.033 from north to south. 43:55.033 --> 43:59.473 But up in Northern Canada actually, south to north. 43:59.467 --> 44:03.867 So it seemed like there's a dome of ice here with a center 44:03.867 --> 44:07.627 somewhere around here, and the ice is then spreading out 44:07.633 --> 44:10.103 gravitationally away from that center. 44:10.100 --> 44:13.930 That's the view or that's the vision you get when you see a 44:13.933 --> 44:15.173 map like this. 44:15.167 --> 44:18.867 Gravity is doing the spreading, and the high point 44:18.867 --> 44:21.727 must have been somewhere in the middle here with ice 44:21.733 --> 44:25.133 moving out in the different directions. 44:25.133 --> 44:27.973 One of the reasons they put a different name on the 44:27.967 --> 44:31.297 Cordilleran ice sheet is because you see some eastern 44:31.300 --> 44:34.030 movement here, which conflicts with what the Laurentide ice 44:34.033 --> 44:35.433 sheet movement has been. 44:35.433 --> 44:39.103 So there must have been a seam here along the Rockies where 44:39.100 --> 44:41.500 those two ice sheets were kind of butting up 44:41.500 --> 44:42.770 against each other. 44:46.167 --> 44:48.227 Questions on that? 44:48.233 --> 44:50.633 That's the Laurentide ice sheet. 44:50.633 --> 44:54.433 Now, down here in New England, we've got this remarkable 44:54.433 --> 45:00.133 feature called Long Island to look at, as well as a Martha's 45:00.133 --> 45:02.473 Vineyard and Nantucket. 45:02.467 --> 45:07.097 When the ice sheet came down here, it moved offshore and 45:07.100 --> 45:09.170 spent a long enough period of time to build 45:09.167 --> 45:11.227 up a terminal moraine. 45:11.233 --> 45:13.703 Then retreated slightly and built up 45:13.700 --> 45:14.670 another terminal moraine. 45:14.667 --> 45:19.797 So there are two terminal moraines that now make up Long 45:19.800 --> 45:23.970 Island, Martha's Vineyard and Nantucket, as 45:23.967 --> 45:27.297 well as Cape Cod. 45:27.300 --> 45:29.330 Those are both--all those features are basically 45:29.333 --> 45:33.373 terminal moraines left over from the Last Glacial Maximum. 45:33.367 --> 45:37.567 So over New Haven here, we probably still had several 45:37.567 --> 45:43.227 hundred meters of ice sliding southwards, but then it 45:43.233 --> 45:48.303 tapered off, and the terminus was roughly here, for a long 45:48.300 --> 45:52.070 enough period of time to have built up two substantial 45:52.067 --> 45:55.927 terminal moraines at those locations. 45:55.933 --> 45:59.233 So we've got evidence right outside our front door that 45:59.233 --> 46:02.273 this ice sheet was overhead not that many years ago. 46:05.000 --> 46:06.270 Questions on that? 46:11.767 --> 46:16.167 Well now, we need to get a little more quantitative about 46:16.167 --> 46:18.797 climate change. 46:18.800 --> 46:20.900 I won't be able to finish this, but let me say a few 46:20.900 --> 46:23.600 words about it and then we'll cut until Wednesday. 46:23.600 --> 46:25.630 But we have to get more quantitative 46:25.633 --> 46:26.303 about climate change. 46:26.300 --> 46:30.730 We have to have records that we can go back uniformly in 46:30.733 --> 46:33.173 time to see how things are changing quantitatively. 46:35.833 --> 46:38.773 One of the best ways to do this is by looking at the 46:38.767 --> 46:42.567 stable isotopes of water. 46:42.567 --> 46:46.227 And I wanted to remind you about what I mean by isotopes 46:46.233 --> 46:48.903 and how we're going to use them climatologically. 46:48.900 --> 46:54.000 You remember that an isotope of a chemical element is 46:54.000 --> 47:00.370 defined as an analog to that element that has an extra 47:00.367 --> 47:08.027 neutron or more in the nucleus to give it an added mass, but 47:08.033 --> 47:12.573 without any change in its electrical charge. 47:12.567 --> 47:22.267 So for example, hydrogen is normally one proton with 47:22.267 --> 47:25.997 electrons going around it. 47:26.000 --> 47:30.770 The most common isotope of hydrogen is called deuterium. 47:30.767 --> 47:35.067 It has a proton and a neutron in its nucleus, so it's got 47:35.067 --> 47:38.297 double the mass, but the same charge. 47:38.300 --> 47:39.930 The same charge means it behaves 47:39.933 --> 47:43.833 chemically like its parent. 47:43.833 --> 47:46.103 But that extra mass makes it behave a little bit 47:46.100 --> 47:49.170 differently when it comes to changing phase. 47:49.167 --> 47:56.167 With oxygen, the dominant, let's say the parent isotope 47:56.167 --> 47:58.867 of oxygen has a mass of 16. 47:58.867 --> 48:03.527 Eight protons, eight neutrons in the nucleus. 48:03.533 --> 48:06.873 However, it's still oxygen if I add two more 48:06.867 --> 48:10.097 neutrons to the nucleus. 48:10.100 --> 48:14.500 Now it becomes oxygen 18. 48:14.500 --> 48:16.200 These are the particular isotopes I'm going to be 48:16.200 --> 48:19.700 talking about next time with respect to using-- 48:19.700 --> 48:23.700 looking for clues for climate change, particularly deuterium 48:23.700 --> 48:28.500 versus hydrogen, and oxygen 18 versus oxygen 16. 48:28.500 --> 48:31.770 So I can make up new water vapor molecules now. 48:31.767 --> 48:35.797 If I make water from a normal--two normal hydrogens 48:35.800 --> 48:39.700 and a normal oxygen, it's going to have a mass of 18 16 48:39.700 --> 48:42.800 plus 1 plus 1, that's 18. 48:42.800 --> 48:45.870 If I replace one of the hydrogens with deuterium, 48:45.867 --> 48:49.197 that's going to give water with a mass of 19. 48:49.200 --> 48:52.530 If instead, I keep the two hydrogens as hydrogen, but 48:52.533 --> 49:01.503 replace the oxygen 16 with oxygen 18, I get a mass of 20. 49:01.500 --> 49:05.200 Turns out that these heavier isotopes of water have a 49:05.200 --> 49:08.930 slightly lower vapor pressure. 49:08.933 --> 49:12.103 This means they evaporate more slowly and they 49:12.100 --> 49:13.370 condense more readily. 49:16.233 --> 49:20.703 And this is what gives them--what provides to us 49:20.700 --> 49:24.170 information about how the hydrological cycle was working 49:24.167 --> 49:28.997 in the past by looking at the ratio of these two isotopes. 49:29.000 --> 49:31.830 I'm out of time today, but before Wednesday if you could 49:31.833 --> 49:35.403 spend a few minutes reviewing your high school and college 49:35.400 --> 49:38.800 chemistry about the nature of these isotopes, that'll put 49:38.800 --> 49:40.230 you in a good position to understand 49:40.233 --> 49:41.473 the lecture on Wednesday.