A. the Earth System

I. The Living Planet

A. The Earth System

The earth is an open system; it receives energy and matter from beyond its boundary and releases energy and matter outside the system. However, the exchange of matter is rather trivial relative to the mass of the earth; yes, meteorites hit the earth, but thankfully they have been very very small. In contrast, the ENERGY the earth receives is huge relative to the energy the earth produces itself (by radioactive decay and geothermal energy). The vast majority of this energy comes from the sun, but we do receive energy from other stars, as well. The difference between the amount we receive from the sun and stars is rather obvious – as plain as the difference between night and day.

Because the amount of matter exchanges beyond the system is very small, we can really think of the earth's matter as a constant amount. Of course, it is changing in type as atoms bond with different things. And all the energy that is used to cause these changes to the earth's matter comes largely from the sun. So, every material thing on earth – coal mines, the air, your cat, your tv, you – represent earthly atoms that have been recombined into their present configuration using largely energy that came from the sun. And these reactions that recombine these atoms are not 100% efficient, so energy is lost. And indeed, since these reactions are changing one type of matter into another and it is not 100% efficient, there is material waste, too…. As well as energetic waste.

How can we figure out and describe how this planet system works? Let's try reductionism.

1. Earth's subsystems

- Lithosphere: This is the rocky, mineral component of the earth system. The earth is about 24,000 km in circumference at the equator, and about 4000 km in radius (from the surface to the center). At this scale, mountains are imperceptible… Mt. Everest is 9km above sea level… roughly 2/1000ths of the earth's radius or 2/10ths of 1% !.

The lithosphere is important to life in lots of ways, since it is the 'planet', after all. But more immediately, it is the source of inorganic nutrients like P, K, Na, and Ca. Phosphorus is in phospholipids and DNA, and all the phosphorus in these components of living cells came from minerals in rock. K and Na are critical to how neurons send electric impulses along, and Ca is what makes proteins in bone rigid. So, we each have a very intimate relationship with the rocks… their elements are in our bodies.

In addition, the crust of the lithosphere is broken into huge plates that float on liquid magma. The movement of these plates has been critical for the evolutionary history of life on earth, isolating organisms when continents separate and bringing organisms into contact with new species when they connect. And, their position and size have changed the climate of the planet, as we will see.

- Atmosphere: These are the gases held by the gravitational field of the Earth. Our atmosphere is 78% nitrogen gas (N2), 21% oxygen gas (O2), and trace amounts of other stuff including CO2 and water vapor.

It is the ultimate source of nitrogen used in living systems, in amino acids and DNA. However, most living systems (like humans) don't get nitrogen from the air directly; the atoms in nitrogen gas are held together too tightly to be broken by any enzymes we have. We breathe it in and breathe it out without using it. But, some bacteria can break the bond, and make other nitrogenous molecules with the released N… binding it to hydrogen in ammonium (NH3) and oxygen in nitrates and nitrates NO2, NO3). Plants can absorb N in these forms and make DNA and amino acids…. And we get the monomers (amino acids and nucleotides) when we eat these plants… we them put our proteins and DNA together using these building blocks. And obviously, oxygen gas is used by life during aerobic respiration.

- Hydrosphere: This is the water on our planet; most of which is in liquid form (with some as water vapor). Of this, most is salt water (97%), and most the freshwater is frozen (2/3). Most of the liquid freshwater is in the groundwater, and only trace amounts – in relative terms – are available to life at the surface of the earth in rivers and lakes. Water is critical to life as the solvent for reactions, and as a stable external and internal environment.

2. Why is the Earth Different?

When we use the comparative method and compare the earth with Venus and Mars, we see that their atmospheres are mostly CO2, with almost 0% oxygen gas. Why is the earth different? Where did all our CO2 go, and where did the oxygen come from?

- The first explanation involves liquid water. CO2 is soluble in water, and will diffuse into water where it reacts with free H+ and forms carbonate and bicarbonate (HCO3, H2CO3). These will react with salt ions in solution like Ca, forming calcium carbonates (Ca2CO3). These are less soluble, and will precipitate out ("settle out") of solution and form limestone deposits. So, simply because
CO2 is soluble in liquid water, CO2 from the atmosphere gets transported through the hydrosphere and becomes limestone rock in the lithosphere. Thus, less CO2 in the atmosphere.

- In addition, there is a second reason involve another of earth's subsystems. Much of the carbon from the atmosphere has been transferred into organic molecules… like proteins, carbohydrates, lipids, and nucleic acids… which now exist in CAROBN-BASED LIFE FORMS. So, the other place the carbon went, besides the lithosphere, is the BIOSPHERE.

3. Interactions

And the biosphere has another effect… it speeds the rates that energy and material flow through/between the other subsystems. So, for instance, marine plankton make shells out of calcium carbonate… this lowers the concentrate of CO2 in the water and increases diffusion into the ocean… and the dead plankton sink, transferring moe calcium carbonate to the lithosphere. Also, plants increase the evaporation of water from the earth's surface, and increase gas exchange to the soil. So, the biosphere affects how the other systems are interacting with one another.

I. What is Ecology?

A. Definition:

The study of the interactions of organisms with one another and with their environment. - Ricklefs Glossary

The scientific study of the distribution and abundance of organisms and their interactions with the environment.

B. Biological Scales

These interactions between organisms and the environment play out across all biological scales from the organism up.

Individuals interacting with environment: harvesting energy, excreting waste, tolerating abiotic conditions.

Populations of individuals: distribution in space/time/demography/genetics, rate of reproduction/death

Communities of populations: diversity, interactions of predation, competition, mutualism

Ecosystems: including the flux of energy and matter through non-living reservoirs

Biosphere: the totality of life and its effects on energy balance and flux through Earth systems (atmosphere, lithosphere, etc.)

C. Ecological Roles

These interactions often involve the flow of energy and matter (and information through communication) between organisms, populations, communities, and ecosystems within the biosphere.

Carnivorous plants

D. Effects: Distribution and Abundance

These interactions can determine the distribution and abundance of organisms across space (where they live at a given time) and through time (when in the ecological development of a community they live).

- developmental changes at the individual level

- changes in abundance, birth/death rates, genetic structure at a populational level

- changes in community composition over time: succession

- evolutionary changes over geologic time

II. Why is Ecology Important?

A. Pragmatic Issues

1. Humans are as dependent as other organisms on "the environment"

- nutrient cycling (decomposition/ release of 'fertilizers')

- atmospheric and climatic regulation (maintaining climate and oxygen levels fit for human existence)

- water and air waste treatment

- food, shelter, and energy (coal, timber)

- recreation and aesthetic value

The cost of replacing these services with man-made constructs has been estimated at 33,268,000,000,000,000/year. Total Gross National product of World is around 30 trillion.

So, that's what "nature" does; it might be important to understand how these systems operate and respond to change.

2. Humans have always affected these systems

- In the past, humans affected local ecosystems and were never able to sustain an equilibrium with their environment. They either moved (Anasazi of U.S.), or went extinct (colonists of Easter Island), or expanded and drew resources from elsewhere as imports. Now that we are affecting the interactions on a global scale and there is no where else "to go", understanding ecological limitations and human impacts becomes a bit more urgent. ‘Extensification’ is using more space; ‘intensification’ is using existing space more intensively.

- Human population has increased 6x in 150 years.

- Now, Global effects: Human Population uses:

40% of primary productivity (E) - massive extinction is a predictable consequence

50% of the freshwater on the planet

83% of land surface has been affected by humans – we are a geological force.

Affect biogeochemical cycles: greenhouse gases, etc. Nobel Prize in chemistry-1996-Scientists demonstrating Greenhouse Effect

Human populations interact with other populations (parasites, prey)and these interactions can be modeled by general ecological theories (spread of AIDS by a few promiscuous people).

B. Sustainability

Brundtland Commission of the U.N. - Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

The agricultural revolution, and the industrial revolution, have allowed humans to exploit resources at huge spatial scales and rapid temporal scales, and we are affecting the way the planet functions. The earth is a “human-dominated system”. The rates at which we are harvesting resources exceeds their rate of replacement – it is not sustainable. How do we create a sustainable system?

- mimicry. A sustainable system already exists – the natural world. We need to study it and learn from it, to see how the natural world achieved sustainability.

C. Biodiversity

a. Utilitarian value:

We use other species as physiological models, and as sources of compounds for drugs and other materials; in addition to recreational use (hunting, fishing) which has a serious economic impact. Chemicals have been isolated from Poison Dart Frogs that is a more potent pain-killer than morphine. Taxol, which was isolated from Yew trees has anti-cancer properties.

- THE LOSS OF GENETIC INFORMATION IS FOREVER.

b. Ecological value:

Diverse communities are more productive and more resistant to change than less diverse communities. We depend on this productivity. Resistance to change means they are more stable – more sustainable over time.

c. Asthetic/Inherent value:

Are we emotionally enriched by it? Do we have an obligation to assist species imperiled by our actions?

And that’s why every biology major must take ecology, and why every FU student must take a course in sustainability…

Study Questions:

1) Why is the earth's atmosphere so different from that of Mars and Venus? Describe two reasons.

2) Define ecology.

3) Describe three reasons why the preservation of diversity is important.

4) How has the distribution and abundance of humans changed over the last 500 years?

5) In particular, most growth has occurred since the industrial revolution. Why?