1 00:00:00,000 --> 00:00:01,604 - [Voiceover] Let's talk a little bit 2 00:00:01,604 --> 00:00:04,328 about the water cycle, which we're all familiar with. 3 00:00:04,328 --> 00:00:06,096 In fact, we're all part of the water cycle, 4 00:00:06,096 --> 00:00:07,509 every moment of our lives. 5 00:00:07,509 --> 00:00:09,312 We might not fully appreciate it. 6 00:00:09,312 --> 00:00:11,011 So let's just jump in the cycle. 7 00:00:11,011 --> 00:00:12,706 I'll start with evaporation. 8 00:00:12,706 --> 00:00:15,288 So we could start with the surface of the ocean here, 9 00:00:15,288 --> 00:00:17,695 or this river, or this lake. 10 00:00:17,695 --> 00:00:19,066 And at any given moment, 11 00:00:19,066 --> 00:00:22,068 there's going to be water evaporating off of that surface. 12 00:00:22,068 --> 00:00:24,832 Water molecules that were in their liquid state, 13 00:00:24,832 --> 00:00:28,644 liquid state, they just have enough energy to bounce away 14 00:00:28,644 --> 00:00:30,811 and go into the gas state. 15 00:00:32,919 --> 00:00:37,069 And water in a gaseous state we call vapor, water vapor. 16 00:00:37,069 --> 00:00:38,652 Water, water vapor. 17 00:00:41,441 --> 00:00:45,395 And so that water vapor, it is going to rise, 18 00:00:45,395 --> 00:00:49,685 likely with the air that has been heated on the surface, 19 00:00:49,685 --> 00:00:54,304 due to the sun, and there's other more complex dynamics 20 00:00:54,304 --> 00:00:57,548 at play, but as it rises, and as the overall temperature 21 00:00:57,548 --> 00:01:01,715 cools, that water vapor will condense into little droplets. 22 00:01:02,646 --> 00:01:04,869 It'll condense around little, tiny air particles, 23 00:01:04,869 --> 00:01:06,953 little particles of dust that you can't even see 24 00:01:06,953 --> 00:01:09,847 with your eye, and that's what forms clouds. 25 00:01:09,847 --> 00:01:14,014 So this is little droplets, so the water's actually back 26 00:01:16,292 --> 00:01:19,323 to the liquid form, they're not individual water molecules 27 00:01:19,323 --> 00:01:23,513 anymore, they're now able to interact with each other, 28 00:01:23,513 --> 00:01:26,947 and they're condensing around these little, 29 00:01:26,947 --> 00:01:31,114 microscopic dust particles to form these water droplets. 30 00:01:31,961 --> 00:01:33,422 And if it's cold enough, they might also form 31 00:01:33,422 --> 00:01:37,572 small ice crystals, and that's what clouds are. 32 00:01:37,572 --> 00:01:40,556 And we see here, they're talking about transportation, 33 00:01:40,556 --> 00:01:42,450 you can have these clouds, we obviously, if you look outside 34 00:01:42,450 --> 00:01:45,841 and you see clouds, those clouds are moving with the wind. 35 00:01:45,841 --> 00:01:48,447 And so they could be moving all of those droplets 36 00:01:48,447 --> 00:01:51,025 with the overall wind. 37 00:01:51,025 --> 00:01:52,598 And when those droplets get heavy enough, 38 00:01:52,598 --> 00:01:55,964 they will precipitate, they will precipitate down. 39 00:01:55,964 --> 00:01:58,888 Now they could precipitate back into where we started, 40 00:01:58,888 --> 00:02:01,349 they could go back to the ocean there. 41 00:02:01,349 --> 00:02:04,231 Or you could go onto a mountain here, 42 00:02:04,231 --> 00:02:07,707 and since if the air is cold enough, 43 00:02:07,707 --> 00:02:09,463 and if you have the right conditions, 44 00:02:09,463 --> 00:02:10,968 that precipitation might be snow, 45 00:02:10,968 --> 00:02:14,589 and it might stay snow right over there. 46 00:02:14,589 --> 00:02:18,513 Or ice, but then eventually things might warm up, 47 00:02:18,513 --> 00:02:20,879 or they might not warm up, but if they do warm up, 48 00:02:20,879 --> 00:02:22,623 well, then, they would melt, 49 00:02:22,623 --> 00:02:25,649 and there would be snow melt run-off. 50 00:02:25,649 --> 00:02:26,837 And that's what you're seeing there. 51 00:02:26,837 --> 00:02:29,674 If that rain is falling in this area, 52 00:02:29,674 --> 00:02:33,990 so let's say it's not cold enough for it to be snow, 53 00:02:33,990 --> 00:02:36,249 we are talking about rain. 54 00:02:36,249 --> 00:02:38,643 Well, most of that water is actually going to 55 00:02:38,643 --> 00:02:41,060 percolate down into the soil. 56 00:02:42,418 --> 00:02:44,603 So most of it goes down. 57 00:02:44,603 --> 00:02:46,628 We look around us and we see these rivers and lakes, 58 00:02:46,628 --> 00:02:48,263 and we say wow, there's a lot of water there. 59 00:02:48,263 --> 00:02:50,368 But it turns out, there's actually a lot more water 60 00:02:50,368 --> 00:02:53,286 inside the ground and obviously, in the ocean. 61 00:02:53,286 --> 00:02:55,227 And we'll talk about that in a little bit. 62 00:02:55,227 --> 00:02:58,620 So you have all of this water that forms 63 00:02:58,620 --> 00:03:01,620 in these underground aquafiers here. 64 00:03:02,604 --> 00:03:05,435 But some of it also ends up in these lakes 65 00:03:05,435 --> 00:03:07,535 and these lakes are usually in a situation where 66 00:03:07,535 --> 00:03:12,070 the ground is either already saturated with water, 67 00:03:12,070 --> 00:03:14,111 or there's the right types of rocks, 68 00:03:14,111 --> 00:03:15,820 so it can contain the water up here, 69 00:03:15,820 --> 00:03:18,798 and similarly, rivers are formed by runoff, 70 00:03:18,798 --> 00:03:22,850 it's snow melt run-off can famously form rivers. 71 00:03:22,850 --> 00:03:25,366 And in general, if you see a creek or a river 72 00:03:25,366 --> 00:03:28,328 near your house, especially when it rains it fills up, 73 00:03:28,328 --> 00:03:31,003 that's a good indication that the ground water's 74 00:03:31,003 --> 00:03:32,926 already saturated and so things are running off 75 00:03:32,926 --> 00:03:34,259 into that river. 76 00:03:35,475 --> 00:03:38,068 And so that in general is the water cycle. 77 00:03:38,068 --> 00:03:39,919 You have evaporation, it condenses into clouds, 78 00:03:39,919 --> 00:03:42,111 it eventually precipitates, and it keeps going, 79 00:03:42,111 --> 00:03:44,037 round and round and round. 80 00:03:44,037 --> 00:03:46,107 Now of course, there's others actors at play. 81 00:03:46,107 --> 00:03:47,894 You have things like plants. 82 00:03:47,894 --> 00:03:51,690 Plants will take up water from the upper soil, 83 00:03:51,690 --> 00:03:54,037 as far as the plant's roots go. 84 00:03:54,037 --> 00:03:57,247 And it will use that water to transport nutrients 85 00:03:57,247 --> 00:03:59,827 down from the soil up into the leaves. 86 00:03:59,827 --> 00:04:02,196 It also uses that water as part of 87 00:04:02,196 --> 00:04:03,759 the photosynthesis process that we've studied 88 00:04:03,759 --> 00:04:05,625 in many videos. 89 00:04:05,625 --> 00:04:09,843 And a lot of that water gets transpired out. 90 00:04:09,843 --> 00:04:12,861 So once again, this is transpiration, essentially, 91 00:04:12,861 --> 00:04:15,503 evaporation out the leaves of the water. 92 00:04:15,503 --> 00:04:18,836 Over here you see this word sublimation. 93 00:04:19,711 --> 00:04:22,885 That's going straight from the solid form of water, ice, 94 00:04:22,885 --> 00:04:27,097 into the gas form of water, or water vapor. 95 00:04:27,097 --> 00:04:29,745 And this will happen in situations where it's cold 96 00:04:29,745 --> 00:04:32,218 and it's very, very, very, very dry. 97 00:04:32,218 --> 00:04:35,501 And you have, in general, low pressure. 98 00:04:35,501 --> 00:04:38,649 So instead of going into the liquid state, 99 00:04:38,649 --> 00:04:40,856 right then the water molecules start just leaving 100 00:04:40,856 --> 00:04:42,106 as water vapor. 101 00:04:44,423 --> 00:04:46,149 And of course, I said, we're part of it. 102 00:04:46,149 --> 00:04:47,297 Well, how are we part of it? 103 00:04:47,297 --> 00:04:49,760 We will drink some of this fresh water, 104 00:04:49,760 --> 00:04:52,108 our bodies are actually mostly water. 105 00:04:52,108 --> 00:04:54,632 The cells in our bodies are 70% water. 106 00:04:54,632 --> 00:04:58,540 Everything we study in biology, water is a key environment 107 00:04:58,540 --> 00:05:01,837 for all of these things to occur. 108 00:05:01,837 --> 00:05:03,587 And then we use that water, 109 00:05:03,587 --> 00:05:07,271 and then we will get that water out of our body, 110 00:05:07,271 --> 00:05:11,749 and then it continues on as part of this water cycle. 111 00:05:11,749 --> 00:05:13,717 Now one thing that I find really interesting, 112 00:05:13,717 --> 00:05:17,576 as an organism that is dependent on fresh water, 113 00:05:17,576 --> 00:05:18,576 when people say fresh water, 114 00:05:18,576 --> 00:05:19,935 we're talking about water without salt, 115 00:05:19,935 --> 00:05:21,768 as opposed to salt water. 116 00:05:21,768 --> 00:05:24,532 So we really need the fresh water in this lake, 117 00:05:24,532 --> 00:05:27,490 or in this river, or we might dig wells, 118 00:05:27,490 --> 00:05:30,762 so that we can get the water out of these aquafiers. 119 00:05:30,762 --> 00:05:33,448 It actually turns out that very little of the overall 120 00:05:33,448 --> 00:05:36,281 water in the world is fresh water. 121 00:05:37,767 --> 00:05:41,140 And so let me show you this chart over here. 122 00:05:41,140 --> 00:05:43,370 I always knew that, but I didn't fully appreciate 123 00:05:43,370 --> 00:05:45,583 how little was fresh water. 124 00:05:45,583 --> 00:05:47,987 So of all the water on our planet, 125 00:05:47,987 --> 00:05:52,740 97.5% is salt water, for the most part, in our oceans. 126 00:05:52,740 --> 00:05:55,061 Only 2-1/2% is fresh water. 127 00:05:55,061 --> 00:05:58,822 And even of that 2-1/2% fresh water, 128 00:05:58,822 --> 00:06:01,428 very little of it is what we traditionally associate 129 00:06:01,428 --> 00:06:03,303 fresh water, the lakes and the rivers. 130 00:06:03,303 --> 00:06:05,150 When I think of fresh water, I'm gonna say oh, 131 00:06:05,150 --> 00:06:06,749 let me go to a lake or a river, 132 00:06:06,749 --> 00:06:08,633 that's stuff that we could potentially drink. 133 00:06:08,633 --> 00:06:11,520 But most of it is actually in glaciers 134 00:06:11,520 --> 00:06:13,827 and permanent snow cover. 135 00:06:13,827 --> 00:06:17,494 So it's ice, snow, that is just not melting. 136 00:06:18,899 --> 00:06:20,466 And it makes you think about what would happen 137 00:06:20,466 --> 00:06:22,292 if this stuff were to melt. 138 00:06:22,292 --> 00:06:24,083 And then you also have ground water, 139 00:06:24,083 --> 00:06:25,456 which we could have access to. 140 00:06:25,456 --> 00:06:28,967 That's why people dig wells, so we're talking about, 141 00:06:28,967 --> 00:06:31,724 well, ground water includes soil moisture, 142 00:06:31,724 --> 00:06:33,813 swamp water, and permafrost. 143 00:06:33,813 --> 00:06:37,637 Very little of the water is actually in lakes and rivers, 144 00:06:37,637 --> 00:06:39,615 which I personally find fascinating. 145 00:06:39,615 --> 00:06:43,299 It wasn't obvious to me before I, frankly, saw this chart. 146 00:06:43,299 --> 00:06:45,178 Now another really interesting thing is, 147 00:06:45,178 --> 00:06:48,294 how long, on average, water molecules might stay 148 00:06:48,294 --> 00:06:50,747 in different parts of this water cycle. 149 00:06:50,747 --> 00:06:53,891 Going back here, you can imagine that a water molecule 150 00:06:53,891 --> 00:06:56,862 can stay for a very long time in the ocean, 151 00:06:56,862 --> 00:06:58,967 especially, you know it's going to be moving around, 152 00:06:58,967 --> 00:07:01,744 depending on ocean currents and temperature 153 00:07:01,744 --> 00:07:03,205 and all of that, but you can imagine, 154 00:07:03,205 --> 00:07:05,500 it could stay in that liquid form in that ocean 155 00:07:05,500 --> 00:07:06,907 for a very long time. 156 00:07:06,907 --> 00:07:09,237 And maybe it spends a shorter amount of time in a cloud. 157 00:07:09,237 --> 00:07:11,338 And people have actually studied this, 158 00:07:11,338 --> 00:07:12,631 which I find fascinating. 159 00:07:12,631 --> 00:07:14,643 I'd be curious to figure out how they actually 160 00:07:14,643 --> 00:07:16,252 got this data. 161 00:07:16,252 --> 00:07:20,601 But this is the average residence time for water molecules. 162 00:07:20,601 --> 00:07:24,896 And you can see here that water can stay in glaciers 163 00:07:24,896 --> 00:07:27,266 and permafrost for a very long time, 164 00:07:27,266 --> 00:07:29,649 we're talking it could be up to 10,000 years, 165 00:07:29,649 --> 00:07:31,002 and these are all rough numbers. 166 00:07:31,002 --> 00:07:33,560 It can stay as ground water anywhere from two weeks, 167 00:07:33,560 --> 00:07:35,906 to 10,000 years, I guess, depending on how isolated 168 00:07:35,906 --> 00:07:37,983 that ground water is. 169 00:07:37,983 --> 00:07:40,591 It could be in the oceans and seas as salt water 170 00:07:40,591 --> 00:07:43,387 for 4,000 years, and we can look at all of these, 171 00:07:43,387 --> 00:07:46,470 all the way, within living organisms, 172 00:07:47,374 --> 00:07:50,353 it'll stay about, on average, a water molecule 173 00:07:50,353 --> 00:07:52,968 will last about a week in the atmosphere, 174 00:07:52,968 --> 00:07:55,860 so that's getting water vapor, turning into a cloud, 175 00:07:55,860 --> 00:07:59,169 precipitating down, on average, one and a half weeks. 176 00:07:59,169 --> 00:08:00,407 And once again, these are averages. 177 00:08:00,407 --> 00:08:01,946 It doesn't mean that every water molecule will stay 178 00:08:01,946 --> 00:08:04,523 exactly one and half weeks in the atmosphere, 179 00:08:04,523 --> 00:08:06,637 but it's a pretty interesting thing to think about, 180 00:08:06,637 --> 00:08:08,578 and it gives you a little bit more sense of, 181 00:08:08,578 --> 00:08:10,118 well, one, where all the water is, 182 00:08:10,118 --> 00:08:12,863 and how it all works together with the water cycle.