Brown hair: Adorable story alert! I was hanging out with my two 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 that's the tier communication
I'm going for with a two year old, but then he said, "Don't
worry there will be more." 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. If my two 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
re-purposed over and over again. 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 phosphorous to move through all
of the earth's various ecological
and geological compartments. Of course we couldn't possibly
talk about how all matter gets
cycled around earth in one video because the earth is pretty big,
but consider this an introduction
to biogeochemical cycles, staring my two personal
favorites, carbon and water. (upbeat music playing) 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 the earth driven by energy supplied
by the sun and the wind. 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. Not only does water cycle
through different places, it also takes different forms in different
places in the cycle, liquid, solid or gas. Since it is 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, graupel, 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 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
flouting 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 graupel. Now the water's on the ground, but
gravity continues to work on it, pulling it towards its resting
place, whatever that might be, it either pulls the water
across the surface of the
land towards the lowest point, in a process called run-off
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 run-off through the creeks, streams and rivers until
it reaches the ocean. 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 onmountain tops, 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 the 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. 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 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 organ
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 dries evaporation
whether it's from the surface of the ocean or from tree tops 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 bit easier to
understand how the carbon cycle works. Carbon's 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. 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 [pam-flow]
of carbon out there because 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. The first biological reservoir is plants. They absorb a bunch of carbon
dioxide out of the atmosphere because they need it to photosynthesize. CO2 is also one of the bi-products
of respiration, the process
by which they use that energy. Plants take in carbon dioxide from
the atmosphere during photosynthesize and then release CO2 back out
into the atmosphere during
their respiration process to make ATP for all
their cellular functions. Right now, you're like
wait, wait, wait, no, isn't the deal that plants get
to take in the carbon dioxide
and animals get to breath 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 things, 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
geological deposits, fossil fuels. Lately, one of humanities very
favorite pastimes is digging
up all of this old carbon in the form of coal and oil and natural
gas and burning it to fuel our ... pretty much everything's,
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 is used by phytoplankton, tiny plant like organisms that form
the base of the marine food chain. They use carbon and 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. 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 geosphere, which is just a fancy word
science-y word for earth rocks. This process is what started
the atmosphere carbon dioxide
levels rising like crazy in the past couple of 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 re-radiating back out into space. So, yeah, our planet is getting warmer because we've been burning through
this massive reservoir of carbon
that we have 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. The situation could be helped
a lot if we would just stop
unlocking all of that carbon and spitting it into the atmosphere, but in some respects we don't have control
of the situation anymore because of ice. Remember how I said that
carbon is often trapped in ice, well in places like Siberia,
and Northern Canada, and Alaska and 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 plants 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 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.