The Hydrologic and Carbon Cycles: Always Recycle! - Crash Course Ecology #8

Key Takeaways

adorable story alert so I was hanging out with my 2-year-old second cousin in the ocean in Florida and we're jumping up and down with the waves and it's fun but then the water got all calm and I said oh no more waves because like that's the top tier of communication I'm going for with a 2-year-old but then he said don't worry there will be more and I was like how do you know and he was like it's a cycle yes it is a cycle the Earth is filled with cycles and if my 2-year-old second cousin knows it you should know it too the universe is the great recycler all the stuff that we've got on Earth every last particle of matter or calorie of energy has been around since the Big Bang it just keeps getting repurposed over and over again and when it comes to matter at least Earth is essentially a closed system all matter gets passed around in continuous biogeochemical cycles which are Pathways for molecules like water or elements like carbon and nitrogen and phosphorus to move through all of the Earth's various ecological and geological compartments now of course we couldn't possibly talk about how all matter gets cycled around Earth in one video cuz the Earth is pretty big consider this an ruction to biogeochemical cycle starring my two personal favorites carbon and [Music] water now I'm sure you already know about at least one kind of planet wide recycling because it's the most obvious to us the hydrologic cycle which describes how water moves on above and below the surface of the Earth driven by energy supplied by the sun and the wind and talking about the hydrologic cycle it's most useful to think about all the water on Earth being held in a series of reservoirs the ocean for instance or the atmosphere in the form of clouds or in polar ice caps so not only does water cycled through different places it also takes different forms at different places in the cycle liquid solid or gas and since it's a cycle there is no beginning and there is no end so where we start our discussion is arbitrary but we're going to start it off with precipitation rain hail snow sleet growle all that stuff is precipitation it happens when water that's being held in the atmosphere condenses or turns from a gas into a liquid and then occasionally freezes into a solid right up in the air the opposite of condensation of course is evaporation the conversion of a liquid into a gas and when a substance converts straight from a solid to a gas that's sublimation and when it's from a gas to a solid that's deposition and now you know back to condensation it's responsible for the formation of clouds which happens when air containing water vapor Rises and cools or is compressed to the point that it can no longer be a gas at this point the vapor forms droplets this is the same thing you see happening on your glass of iced tea on a humid day the water in the air around the glass gets cold and turns from gas into liquid so a cloud is just a big pile of condensed water droplets in a sense it's a gigantic floating Reservoir clouds are a handy feature of the hydrologic cycle because as they drift over the landscape they move water around the globe so water that evaporates over the ocean can be deposited somewhere else otherwise if water always got deposited right where it evaporated the precipitation would be almost all right over the ocean because that's where most of the evaporation on Earth takes place so wind moves clouds and as water keeps condensing clouds get heavier and heavier until our old friend gravity takes over and pulls the condensed droplets to the ground in the form of rain or in the form of snow or hail or sleet or grel so now the water's on the ground but gravity continues to work on it pulling it toward its resting place whatever that might be it either pulls the water across the surface of the land toward the lowest point in a process called runoff or it pulls it underground water can be trapped or stored for a little while in places like lakes and ponds and wetlands but most of the water that falls this precipitation gets pulled lower and lower and lower as run off through the Creeks streams and rivers until it reaches the oceans now in really cold places water of course freezes and hangs around as ice in certain places for thousands of years at a time like at the poles and Glaciers and on Mountain Toops but when it melts most of it too runs off into the oceans so you see where this is going oceans are a big deal they're pretty much the biggest deal they're the reason that we have the hydrologic cycle in the first place they're also the reason we have awesome stuff like weather and life on Earth the weird thing about oceans though is that they're salty and there is a reason for this as water runs to the ocean it erodes minerals like salt from soil and carries it to the ocean now water heading to the ocean might not taste salty but the salt's in there but here's the thing when the water evaporates again the salt doesn't evaporate with it it gets left behind you keep this up for a few billion years with pure water evaporating from the ocean and then returning with tiny amounts of salt and that's your recipe for a billion cubic kilometers of Brine and all this shows that the world's oceans are literally the last stop for all the liquid water on Earth the only way to get out of there is through evaporation and that leaves all your minerals behind now living things also have their role to play in the hydrologic cycle in both plants and animals the breakdown of carbohydrates to produce energy produces water as a waste product so we lose water through evaporation from our skin we also exhale water vapor and of course we pee it out indeed most organisms on Earth are made mostly of water although that water cycles in and out of us pretty quickly in Plants water is sucked up through the roots and moves up to the leaves the gas exchange organs where it evaporates quickly this process is called evapo transpiration and since there are so many plants here on Earth it's responsible for a good amount of the water that enters the atmosphere this process is essentially the opposite of condensation and that it turns liquid water into gas the energy of the sun drives evaporation whether it's from the surface of the ocean or from Treetops and leaves and then once all that water evaporates into the atmosphere we're right back where we started it's a cycle so now that you know a little bit about the hydrologic cycle it's a little easier to understand how the carbon cycle works carbon is one of the most abundant elements in the universe and here on Earth it's always on the move just like water jumping from one reservoir to the next and that's a good thing because a all living things require carbon for their structure and to fuel their bodies and B it's a big component in a bunch of non-living things as well it's in rocks and the ocean trapped in ice plus it's in the atmosphere where it helps regulate the temperature without carbon dioxide Earth would basically be a frozen Wasteland so lucky for us there's a whole pants load of carbon out there cuz we need it let's start out with the carbon in living things if you were to take all of the water out of your body carbon would constitute about half of what remained in the little pile of dust that used to be you and the first biological carbon Reservoir is plants they absorb a bunch of car carbon dioxide out of the atmosphere because they need it to photosynthesize but CO2 is also one of the byproducts of respiration the process by which they use that energy so plants take in carbon dioxide from the atmosphere during photosynthesis and then release CO2 back out into the atmosphere during their respiration process to make ATP for all their cellular functions and right now you're like wait wait wait didn't no isn't the deal that plants get to take in the carbon dioxide and animals get to breathe it out well yes and no it's just that plants take in more CO2 from the atmosphere than they give off through respiration the rest is like their profit it's what becomes the body of the plant that's right that big old massive tree all of that mass came from gas pretty cool so carbon absorbed by plants has three possible fates it can be respired back into the atmosphere it can be eaten by an animal or it can be present when the plant dies and if a tree falls in the right kind of forest and it's not allowed to decompose normally because a bunch of other plants all fell right on top of it and they die and get buried and squished together and form rocks like coal we call these carbon rich gelot iCal deposits fossil fuels lately one of Humanity's very favorite pastimes is digging up all this old carbon in the form of coal and oil and natural gas and burning it to fuel our pretty much everything but I'll get to that later another extremely important carbon Reservoir is the ocean now carbon dioxide dissolves really easily in water and once it's in there a lot of it's used by phytoplankton tiny plant-like organisms that form the base of the marine food chain they use carbon in photosynthesis and they also use it to make calcium carbonate shells and when these guys die their shells settle to the bottom of the ocean pile up become compressed and over time make rocks like Limestone now Limestone obviously doesn't burn super well so it's not considered a fossil fuel but as Limestone deposits are eroded by water the calcium carbonate is broken down to eventually form among other things carbon dioxide and carbonic acid we make lime and cement by heating Limestone which produces a pretty good amount of carbon dioxide and when we do burn fossil fuels such as coal and petroleum products and natural gas it also releases carbon in the form of carbon dioxide that's been stored for hundreds of millions of years in the Geo spere which is just a fancy sciency word for Earth rocks this process is what started the atmospheric carbon dioxide levels Rising like crazy in the past couple hundred years and the excess of carbon dioxide in the atmosphere causes global climate change because CO2 in the atmosphere prevents some of the sun's energy from reradiating back out into space so yeah our planet is getting warmer because we've been burning through this massive reservoir of carbon that we had locked underground this is causing all kinds of problems that we can see already and it's very likely going to keep causing bigger and bigger problems with time and the situation could be helped a lot if we would just stop unlocking all that carbon and spitting it in the atmosphere but in some respects we don't even have control of the situation anymore because of ice remember how I said the carbon is often trapped in ice well in places like Siberia and Northern Canada and Alaska cold places that also have plants they contain huge carbon reserves that are trapped in permafrost ground that's frozen year round these places are basically Frozen Wetlands that add another layer of dead plant matter each year but as permafrost melts these dead plants decompose and huge amounts of carbon dioxide and methane are released into the atmosphere creating a positive feedback loop our carbon burning Lifestyles unleashing this other huge carbon Reservoir which keep the whole greenhouse effect going with or without us just saying sorry to end on such a frightening and depressing note but the stability of global climate is not as stable as we would like it to be and the fact that we're throwing it out of whack is one of the most important reasons to study ecology in the first place this episode of Crash Course was written by myself jeline Shields and Blake de pastino our technical director is Nick Jenkins who was also our editor and is also standing behind the camera right now Graphics are courtesy of Amber Bushnell and Peter Winkler and our sound designer is Michael Londa if you want to review any of what we went over in today's episode check out the table of contents over there and if you have any questions or comments or Corrections or ideas for us we're on Facebook and Twitter and of course down in the comments below