In this video we're going to describe the components of the Earth's system
and explore how matter is exchanged between each of the four main spheres of the system.
Although Earth looks like one large structure the air, water, rocks, and life are representatives of
interconnected components or "spheres" in the Earth system.
Matter cycles between these system components.
Scientists think of the movement of matter as the rate of flow or flux of materials
moving into and out of a series of reservoirs.
We'll describe a simplified example of the oceans as a reservoir.
Water circulates into the oceans from various sources
including rainfall and rivers.
Water flows out by evaporation to the atmosphere.
As long as the rate of water leaving the system is balanced with the rate of water entering the system
the size of the reservoir remains the same and sea level doesn't change.
However, during the last ice age, frozen precipitation that fell on the continents
was trapped in ice sheets and didn't return to the ocean.
Consequently, sea level dropped significantly by more than a hundred meters.
In recent years the rate of melting of glaciers on the continents has intensified.
This has increased flow into the system, producing
a larger reservoir and a rise in global sea levels.
The earth system can be characterized by the flow of matter through reservoirs in each of the major spheres.
We will describe each part of the system,
the relationships between the parts, and how those relationships may change over time.
To help us do this we will take a closer look at how different forms of a key element, carbon,
moves among the components of the system.
We will start with the atmosphere.
We live in the lowest layer of the atmosphere and this layer contains all the weather that we experience
plus all the air that we breathe.
The air includes a small fraction of carbon dioxide
along with the more abundant nitrogen and oxygen gases.
This tiny amount of carbon dioxide makes an outsized contribution to Earth's climate.
Carbon dioxide naturally flows into the atmosphere
as a result of the decomposition of organic materials and forest fires.
The concentration of atmospheric carbon dioxide
has increased as a result of the greater use of carbon rich fossil fuels.
This plot, known as the Keeling Curve, records the study increase of carbon dioxide in the atmosphere.
The world's oceans represent the vast majority of the hydrosphere.
Carbon dioxide and other gases are exchanged between the atmosphere and the ocean.
The carbon becomes part of a carbonate ion that combines with calcium to form the mineral calcite
as it becomes part of the biosphere to build shells for things like oysters and clams,
as well as billions of microscopic organisms like these coccolithophores.
The rock limestone forms when these organisms die and are buried
and compacted into layers of rock on the seafloor.
Thus matter moves from the biosphere to the geosphere.
The geosphere includes the continents and ocean floors,
and the rocks and minerals in Earth's crust, mantle and core.
Most rocks remain in the geosphere for millions of years making them part of the Earth's largest carbon reservoir.
There is more carbon stored in the geosphere's fossil fuel reserves
than there is throughout all of Earth's biosphere.
The biosphere is composed of all the living organisms on the planet
this is everything from vegetation on the continents to microscopic phytoplankton in the oceans and
familiar complex organisms like elephants and birds
and let's not forget humans
Most of the carbon in the biosphere is present as plant material, or is found in soils.
Plants take in carbon dioxide from the atmosphere through photosynthesis
and combine it with other elements to form carbohydrates needed for growth.
Soils contain more carbon than plants, most of it in the form of decaying plant material
and living biomass of microbes that help break down the dead plant matter.
So, now we know a little bit more about each part of the Earth's system
and some of the relationships between the parts.
Next, we will look at an example of how those relationships change over time.
If we want to think more deeply about how the earth system works
we might begin by considering a quote by conservationist John Muir.
He noted that "Whenever we try to pick out anything by itself
we find it hitched to everything else in the universe."
Or, to put in the context of the earth system;
if we change part of one earth system component
it will result in changes in the other parts of the system as well.
That's exactly what has happened in the case of the world's carbon.
This figure shows the relative sizes of the carbon reservoirs within each component of the earth system.
Note that the geosphere has the largest amount of carbon and the atmosphere has the least.
However, while the atmosphere is the smallest of the reservoirs it experiences the largest relative flux.
In contrast, material moves in and out of the natural geosphere as for very slowly over millions of years.
It's only when human actions perturb this reservoir that it experiences more rapid flux.
For example up to a few hundred years ago
the flow of carbon among some of the system components would have looked something like this.
With the carbon exchange between the different spheres being relatively similar.
However, after the Industrial Revolution
there was a rapid increase in fossil fuel use and significant land use changes.
Consequently, today's version of this figure illustrates that we now release
approximately nine gigatons of carbon each year from the geosphere through human activities.
Much of the additional carbon is added to the atmosphere but some of it finds its way
to the hydrosphere and is added to the world's ocean as part of the air-sea gas exchange process.
Also, the biosphere mops up some of the additional carbon adding it to plants and soil organisms.
However, even with the carbon added to the biosphere and hydrosphere,
there's still four gigatons unaccounted for that are added to Earth's atmosphere;
explaining the steady increase in the Keeling Curve that we described earlier.
So, our review of the Earth's system, helps us understand that
if we wanted to halt the increase of carbon in the atmosphere
we'd have to either, reduce human production of carbon by about half,
or find ways to increase the uptake of carbon in other earth system components.
We had three learning objectives for today's lesson.
How confident are you that you can complete these tasks?
