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

Summary

This script narrates the enchanting encounter between a storyteller and a 2-year-old, leading to an exploration of Earth's cycles, particularly the hydrologic and carbon cycles. It explains how water and carbon are continuously recycled through ecosystems and geological processes, highlighting the importance of these cycles for life and climate. The script also addresses human impact, particularly how burning fossil fuels contributes to climate change, urging the importance of understanding ecological cycles.

Takeaways

• 🌊 The ocean plays a central role in the hydrologic cycle, being the largest reservoir of water on Earth and influencing weather and life.
• 🔄 The hydrologic cycle involves the continuous movement of water in its various states (liquid, solid, gas) through the Earth's ecosystems and atmosphere, driven by solar energy and wind.
• 💧 Precipitation, including rain, hail, snow, and sleet, marks the beginning of the water's journey from the atmosphere back to the Earth's surface.
• 🌧️ Clouds are formed by the condensation of water vapor in the atmosphere, serving as floating reservoirs that transport water across the globe.
• 🌿 Plants contribute to the water cycle through evapotranspiration, releasing water vapor back into the atmosphere, which is a significant part of global water movement.
• 🏞️ Runoff and infiltration are processes by which water moves across land surfaces or seeps into the ground, eventually making its way to oceans or other water bodies.
• 🧊 The salinity of oceans is a result of dissolved minerals carried by water from the land, which are left behind when water evaporates.
• ♻️ The carbon cycle is a global process where carbon moves between living organisms, the atmosphere, oceans, and geological formations.
• 🌳 Plants are primary biological carbon reservoirs, absorbing CO2 for photosynthesis and releasing it during respiration, with the excess carbon contributing to their growth.
• 🔥 The burning of fossil fuels releases stored carbon dioxide into the atmosphere, contributing to global climate change and increasing atmospheric CO2 levels.
• ❄️ Permafrost melting releases large amounts of CO2 and methane due to the decomposition of trapped organic matter, creating a feedback loop that exacerbates the greenhouse effect.

Q & A

What is the main theme of the video script?

The main theme of the video script is the concept of biogeochemical cycles, focusing on the hydrologic and carbon cycles as examples of how matter is continuously recycled on Earth.

Why are oceans considered the last stop for all the liquid water on Earth?

Oceans are considered the last stop for all the liquid water on Earth because they are the ultimate destination for water that has undergone the process of runoff from land. The water can only leave the ocean through evaporation, leaving behind dissolved minerals such as salt.

What is the hydrologic cycle, and what are its key components?

The hydrologic cycle is the process by which water moves on, above, and below the Earth's surface, driven by the energy from the sun and the wind. Key components include precipitation, evaporation, condensation, and the movement of water through runoff and groundwater flow.

How does the process of evapotranspiration contribute to the hydrologic cycle?

Evapotranspiration is the process by which plants absorb water through their roots and release it into the atmosphere through their leaves. This contributes to the hydrologic cycle by adding water vapor to the atmosphere, which can then condense to form clouds and eventually precipitate as rain or snow.

What is the role of phytoplankton in the carbon cycle?

Phytoplankton play a crucial role in the carbon cycle by using carbon dioxide for photosynthesis, which also contributes to the formation of calcium carbonate shells. When these organisms die, their shells sink to the ocean floor, contributing to the formation of carbon-rich rocks like limestone.

Why is the burning of fossil fuels a significant concern in the context of the carbon cycle?

The burning of fossil fuels is a significant concern because it releases large amounts of carbon dioxide that has been stored in the Earth's geosphere for millions of years. This contributes to the increase in atmospheric CO2 levels, leading to global climate change.

What is the impact of melting permafrost on the carbon cycle?

Melting permafrost releases large amounts of carbon dioxide and methane that were previously trapped in the frozen ground. This release contributes to the greenhouse effect and global warming, creating a positive feedback loop that exacerbates climate change.

How does the carbon cycle relate to the structure and function of living organisms?

The carbon cycle is integral to the structure and function of living organisms because carbon is a fundamental component of their biological molecules. Through processes like photosynthesis and respiration, organisms take in carbon dioxide and release it back into the atmosphere, contributing to the cycle.

What is the significance of the carbon cycle in regulating Earth's temperature?

The carbon cycle is significant in regulating Earth's temperature because carbon dioxide in the atmosphere plays a role in trapping heat. An imbalance in the carbon cycle, such as increased CO2 levels due to human activities, can lead to global warming.

How does the script use the anecdote with the 2-year-old to introduce the concept of cycles?

The script uses the anecdote with the 2-year-old to illustrate the concept of cycles in a relatable and engaging way. The child's understanding of waves as a cycle serves as a simple introduction to the more complex cycles of matter on Earth, such as the hydrologic and carbon cycles.

What is the role of the sun in driving the hydrologic and carbon cycles?

The sun plays a crucial role in driving both the hydrologic and carbon cycles by providing the energy necessary for processes such as evaporation and photosynthesis. This energy allows water to move from the Earth's surface into the atmosphere and enables plants to convert carbon dioxide into organic matter.

Outlines

00:00

🌊 The Wonders of Earth's Hydrologic and Carbon Cycles

This paragraph introduces the concept of cycles on Earth, starting with a personal anecdote about waves at a Florida beach with a 2-year-old cousin. It explains the hydrologic cycle, detailing how water moves across the Earth's surface and atmosphere through precipitation, evaporation, condensation, and other processes. The importance of oceans in the cycle is highlighted, along with the role of living organisms like plants and animals in the cycle. The paragraph also touches on the carbon cycle, emphasizing its relevance to life and the environment, and introduces the idea of biogeochemical cycles, focusing on carbon and water as key elements.

05:02

🌿 Deep Dive into the Carbon Cycle and Its Impact on Climate

The second paragraph delves deeper into the carbon cycle, illustrating how carbon moves between different reservoirs on Earth, including living organisms, the atmosphere, and geological formations. It describes the process of photosynthesis and respiration in plants, the formation of fossil fuels, and the consequences of burning these fuels, which contribute to the rise in atmospheric carbon dioxide levels and global climate change. The paragraph also discusses the role of the ocean as a carbon reservoir, the creation of calcium carbonate shells by phytoplankton, and the potential release of carbon from melting permafrost, which could exacerbate the greenhouse effect. The summary concludes with a call to action regarding the importance of studying ecology in light of human-induced climate change.

Keywords

💡Biogeochemical Cycles

Biogeochemical cycles refer to the pathways through which molecules and elements such as water, carbon, nitrogen, and phosphorus move through Earth's ecological and geological systems. In the video, these cycles are introduced as a fundamental concept to understand how matter is continuously recycled on Earth, with a focus on the carbon and water cycles as key examples.

💡Hydrologic Cycle

The hydrologic cycle, also known as the water cycle, describes the continuous movement of water on, above, and below the Earth's surface. It is driven by solar energy and wind, involving processes such as evaporation, condensation, precipitation, and runoff. The script uses the hydrologic cycle to illustrate how water is distributed globally and the importance of oceans in this process.

💡Precipitation

Precipitation encompasses rain, hail, snow, sleet, and graupel, which occur when atmospheric water vapor condenses into liquid or solid forms. The video script explains that precipitation is a critical part of the hydrologic cycle, starting the journey of water from the atmosphere back to the Earth's surface.

💡Condensation

Condensation is the process by which water vapor in the air turns into liquid, forming droplets that can lead to cloud formation. The script mentions condensation as a key mechanism in the creation of clouds, which are essential for the movement of water around the globe.

💡Evaporation

Evaporation is the conversion of liquid water into water vapor, a process that is central to the hydrologic cycle. The script explains that evaporation occurs when water from the Earth's surface, including oceans, turns into vapor due to the sun's energy, contributing to cloud formation and the overall water cycle.

💡Carbon Cycle

The carbon cycle is the process by which carbon atoms move through Earth's atmosphere, oceans, and land. It is vital for life as carbon is a fundamental component of all living organisms and plays a significant role in regulating Earth's temperature. The video script discusses the carbon cycle in the context of how carbon moves between different reservoirs, such as the atmosphere, plants, and the geosphere.

💡Fossil Fuels

Fossil fuels, such as coal, petroleum, and natural gas, are carbon-rich geological deposits formed from the remains of ancient plants and animals. The script explains that burning fossil fuels releases stored carbon dioxide into the atmosphere, contributing to global climate change.

💡Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert carbon dioxide and sunlight into organic compounds, releasing oxygen as a byproduct. The video script highlights photosynthesis as a primary means by which plants absorb carbon dioxide from the atmosphere, playing a crucial role in the carbon cycle.

💡Respiration

Respiration is the process by which living organisms convert organic compounds into energy, releasing carbon dioxide as a byproduct. In the script, it is mentioned that plants release carbon dioxide back into the atmosphere through respiration, but they absorb more through photosynthesis, contributing to the carbon cycle.

💡Permafrost

Permafrost refers to ground that remains frozen throughout the year, often containing large amounts of carbon in the form of frozen organic matter. The script discusses how the melting of permafrost can release carbon dioxide and methane into the atmosphere, exacerbating global warming.

💡Global Climate Change

Global climate change refers to the long-term shifts in Earth's climate, particularly the increase in average global temperatures. The video script connects global climate change to the increase in atmospheric carbon dioxide levels due to human activities such as burning fossil fuels and deforestation.

Highlights

A 2-year-old's understanding of the concept of cycles is introduced as a metaphor for Earth's biogeochemical cycles.

The Earth is described as a closed system for matter, with continuous recycling of particles and energy since the Big Bang.

Biogeochemical cycles are pathways for molecules and elements like water, carbon, nitrogen, and phosphorous through Earth's ecological and geological systems.

The hydrologic cycle is introduced as the planet-wide recycling process driven by the Sun and wind.

Water exists in different forms and reservoirs such as oceans, atmosphere, and polar ice caps within the hydrologic cycle.

Precipitation, including rain, hail, snow, and sleet, is explained as a phase change from gas to liquid or solid.

Condensation and the formation of clouds are described as pivotal processes in the water cycle.

The role of gravity in moving water through runoff and infiltration into the Earth's surface is highlighted.

Oceans are identified as the ultimate resting place for water, with salt accumulation due to evaporation.

The importance of the hydrologic cycle in supporting life and weather patterns on Earth is emphasized.

Plants and animals contribute to the water cycle through transpiration and respiration, releasing water as a byproduct.

The carbon cycle is introduced as a critical process involving the movement of carbon through various reservoirs.

Plants act as carbon reservoirs, absorbing CO2 for photosynthesis and releasing it during respiration.

Carbon's role in the structure of living organisms and its presence in non-living components like rocks and the atmosphere is discussed.

Fossil fuels are described as carbon-rich geological deposits formed from ancient plant matter.

The burning of fossil fuels and its impact on atmospheric CO2 levels and global climate change is examined.

Permafrost as a carbon reservoir and the potential release of CO2 and methane due to melting is presented as a climate change feedback loop.

The episode concludes with a call to understand ecology in light of human-induced climate change and its implications for global climate stability.

Transcripts

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'll 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 of the stuff we have 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, the Earth is essentially a closed system.

All the matter gets passed around in continuous biogeochemical cycles,

which are pathways for molecules like water or elements like carbon and nitrogen and phosphorous

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,

'cause the Earth is pretty big,

but consider this as an introduction to biogeochemical cycles starring my two personal favorites:

carbon and water.

[Theme Music]

Now I'm sure you already know about at least one type 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 the energy supplied by the Sun and the wind.

In talking about the hydrologic cycle it's most useful to think about all of 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 cycle through different places,

it also takes different forms in different places in the cycle: liquid, solid, or gas.

And since it's a cycle there is no beginning and no end, so where we start our discussion is arbitrary,

but we're going to start it off with precipitation.

Rain, hail, snow, sleet, graupel, all of 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, it 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. But back to condensation.

It is 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 ice 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 always 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 graupel.

So now the water's on the ground,

but gravity continues to work on it pulling it towards its resting place wherever that might be.

It either pulls the water across the surface of the land to 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 as precipitation gets pulled lower and lower and lower

as runoff through the creeks and streams and rivers until it reaches the ocean.

In really cold places, water of course freezes and hangs around as ice in places for thousands of years at a time,

like at the poles and glaciers and on mountaintops, but when it melts, most of it too runs off into the ocean.

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 that 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 may 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 the pure water evaporating from the ocean

and returning with tiny amounts of salt and that's your recipe for a billion cubic kilometers of brine.

And all of this shows us 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,

and both plants and animals that break down carbohydrates to produce energy produces water as a waste product.

So we lose water through evaporation from our skin and 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 evapotranspiration. 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 in that it turns liquid water into gas.

The energy of the sun drives evaporation whether it's the surface of the ocean or from treetops and leaves,

and then once all of 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, in 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, 'cause we need it!

Let's start off 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 carbon dioxide out of the atmosphere because they need it to photosynthesize.

But CO2 is also one of the by-products 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-no isn't it the deal that plants get to take in all 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 though respiration.

The rest is like their profit; it's what becomes the body of the plant.

That's right, that big-ol' massive tree, all 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 they get buried and squished together and form rocks like coal.

We call these carbon-rich geological deposits fossil fuels.

Lately one of humanity's very favorite pastimes is digging up all of this carbon

in the form of carbon and natural gas, and burning it to fuel our, pretty much everythings.

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 all of it's used by phytoplankton

(tiny plant-like organisms that form the base for the marine food chain).

They use it to do photosynthesis and they also use it to form 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 gases

it also releases carbon in the form of carbon dioxide that's been stored for hundreds of

millions of years in the geosphere,

which is just a fancy science-y word for Earth-rocks.

This process is what started the atmosphere carbon dioxide rising like crazy in the past couple of hundred years.

And the excess of the carbon in the atmosphere causes global climate change,

because CO2 in the atmosphere causes some of the sun's energy from re-radiating back out into space.

So yeah, our planet has been getting warmer because we've been burning through this 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 to keep causing bigger and bigger problems with time.

And the situation could be helped a lot if we could just stop unlocking all of that carbon

and spitting it into the atmosphere,

but in some respects we don't even have control over the situation any more, because of ice.

Remember how I said that 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 lifestyle is releasing this other huge carbon reservoir,

which keep the whole greenhouse effect going with or without us. Just sayin'

Sorry to end on such a frightening and depressing note,

but the stability of the 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, Jesslyn Shields, and Blake de Pastino.

Our technical director is Nick Jenkins who is 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 Aranda.

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.