so what we're learning from all of this is that to live sustainably we have to not deplete what Miller in some editions calls capital and in other editions he calls it natural capital natural capital relates to all this stuff it includes Earth's ability to repair damage to clean up after us often called ecosystem services what do we mean by us cleaning up after us well every day we put more pollution into the air yeah it doesn't get worse all the time because nature cleans them if nature's rate of cleaning the air is greater than the rate at which we had pollution yes days good but unfortunately in Southern California as we saw and we were discussing smart a while ago oftentimes especially in summer the pollution is not allowed to escape it builds up it gets ahead of nature's ability to repair the damage and we experience bad air quality water nature constantly takes our polluted water and returns us clean water is apples through the natural water cycle evaporation and precipitating team water back somewhere else but water quality looks like depends on the rate at which we add pollution to water versus the rate at which nature cycles and purifies the water any other examples ecosystem services the other important aspect of Earth capital is the things that we get from the earth resources sometimes also called natural resources that's kind of unnecessary resources are natural so at this point we're ready for a definition of sustainability or sustainable living sustainable living means using the earth's resources we've got to use them we live on become just not use them using the earth's resources no faster that they can be replaced okay sustainable living using the earth's resources no faster than they can be replaced clarification when I say then they can be replaced do I mean replaced by us or do I mean replaced by nature right nature how does nature replace resources well take a forest for example you cut down trees new trees grow to replace them you catch fish the fish that are left breed make more fish so replace what the resources is obvious how it works with biological resources replacement is biological reproduction but they are not living in animate resources that replace themselves naturally also take for example groundwater what is groundwater groundwater is water in the ground water in cracks and crevices porosity remember porosity in the ground how does water get into the ground to become groundwater from rain rain falls on the ground soaks it that's all the rainwater soak into the ground no much soaks into the ground varies from place to place on a steep slope or if the rain runs off on level ground it'll sit there Tector soak in warmer temperatures more of it evaporates cooler more of it stays the permeability of the soil if it's easy for water to go in will go in if it's relatively impermeable water just since then so there's a rate at which water can soak into the ground and become groundwater different everywhere but there is a limiting rate there is on the other hand no particular limit to how many wells we can drill and how fast we can pump water out of those wells if we pump water out faster than nature is replacing it we're depleting the resource that we will run out if we are careful to pump it out not as fast as nature replaces it then we'll have ground water forever by the way about four years ago California became the only place certainly in the nation and I think the world to have a law in place that makes it illegal to pop out groundwater faster than a sustainable rate okay so there are lots of resources that do replace themselves in action then there are resources that don't where what we've got on planet earth is all there is there's no way to get more as we use them up we eventually come to a point where we run out there's nothing left those include the things that we dig out of the earth like the fossil fuels like the minerals take metals like aluminium the aluminum or present in the Earth's crust is all there is once you've used it up there'll be no more how can we avoid running out of aluminium we stretch it out and maybe keep it available forever recycling recycling means that instead of every time we need more aluminium going back and digging more aluminum ore out of the ground we use the same aluminum that we've used already instead of sending it to the trash if we want to truly extend aluminium so that we never run out of it how much of it do we have to recycle all of it yes so why are we doing that not even close then of course there are some resources that don't review themselves naturally and they're not recyclable the fossil fuels particularly come to mind yeah because when we use a fossil fuel what do we do we burn it we destroy it it's gone no such thing as recycled gas on those we're guaranteed to run out of okay I'd now like to formalize this concept of resources a little bit using this very important diagram if you have one of the older textbook editions that I recommended you have this diagram it's been removed from the newer editions unfortunately and it's replaced by two pages of text in which the key terms are bolded I think the diagram is very healthy I expect all of you have heard of the - a division of resources into renewable and nonrenewable this you'll notice is a slightly more sophisticated classification with a three-way split here are the non-renewable resources as in the two-way classification here are renewable resources qualified as potentially renewable the potentially is there so that we understand that these are resources that in the course of natural events we would expect to renew themselves but we can screw those up we can damage or deplete them to the point that they are no longer renewable the third extra group in the classification over here labeled as perpetual or in latest book he's renamed these he's now calling them inexhaustible so what's the difference these resources here replace themselves renew themselves these ones are just there the word perpetual what does it mean if something is perpetual it will last forever perpetual means forever inexhaustible means cannot run out so that's the same thing so yes these are resources that we cannot run out of we don't have to worry about over consuming these until they're no longer available that makes these into a very important group of resources as our population increases as our environmental demand increases and as we put more and more pressure on the other resources okay so what we're going to do now is we're good to look at these in turn we'll look at these perpetual resources first then we'll look at the potentially renewable resources and finally we'll take a look at these non-renewable resources over here