Let’s Review the Physical Laws of Matter and Energy
A course in ecological theory would include more details on these and other biogeochemical cycles such as Nitrogen, Phosphorous, Potassium that affect ecosystems.
However, our examination of the rock, water, carbon and oxygen cycles provides us with the crucial information we need for this discussion.
What we have learned about the laws of matter and energy can be summarized by the phrase: Energy Flows and Matter Cycles. The sun is the source energy which drives biogeochemical cycles with additional gravitational and heat energy from the earth.
It is important to understand these fundamental scientific laws because the earth’s environment and all life evolve within the constraints of these laws. This goes for human activities too!
With that in mind, let’s look more closely at how living systems use energy and matter.
Matter, Energy and Living Systems
As we’ve said, in all-natural systems, energy flows and matter cycles. The sun continually produces energy, which degrades from higher to lower quality and eventually dissipates in the form of heat.
The sun is the ultimate source of energy available to us on Earth.
Thermonuclear fusion in the sun converts Hydrogen to Helium atoms, releasing tremendous amounts of radiation in every direction. This radiation occurs in all wavelengths – from x-rays and gamma rays through long wave radiation. Only about 50% of it occurs in the visible light spectrum.
Since the sun is a sphere and radiates in all directions, only a small portion of the energy released by it is actually absorbed by the Earth (or any other body in our solar system). The amount of solar energy that hits the Earth is finite and, though not limitless, represents a lot of energy – approximately 120,000 terawatts (TW) per hour more than humans use which is about 15 TW of power per year. This is the energy that runs all living systems. All life from the depths of the ocean, to the tops of the mountains, sustains itself with this energy. This absorbed energy is called Solar Flux.
Figure 1-4 below describes what happens to the sun’s energy when it strikes the earth’s surface.
Figure 2-4 Earth’s energy budget.
Credit: Image courtesy NASA’s ERBE (Earth Radiation Budget Experiment) program.
26% of the sun’s energy that hits the Earth’s atmosphere is reflected before it even gets to the surface. Another 4% is reflected off the earth’s surface. The reflectivity of a body’s surface is called its albedo.
In total, almost a third of the sun’s energy is reflected. The energy striking the earth’s surface averages about 240 Watts per cubic meter (W/m3) and results in an average surface temperature of 14 degrees C (57 degrees F).
Being a stable, balanced system, the Earth must radiate 240 W/m3 of energy. If something were to cause the atmosphere to hold more heat than it currently does, the Earth would continue to heat up until it reached a new energy equilibrium at a warmer temperature. Once the new balance was reached, assuming the sun’s energy to be constant, we would again find 240 W/m3 of energy entering and 240 W/m3 of energy exiting a warmer earth atmosphere.
Notice that the total amount of energy leaving the earth equals the amount of energy input by the sun regardless of the atmospheric temperature. In other words, 240 W/m3 delivered by the sun is always balanced by the same amount of energy radiated off the earth.
Much of the energy leaving the earth does so in the form of latent heat contained in water vapor which has evaporated from rivers, lakes and oceans.
A lot of energy in the form of latent heat is moved around the planet with the movement of water in the water cycle. According to the US Geological Survey, “about 71 percent of the Earth’s surface is water-covered, and the oceans hold about 96.5 percent of all Earth’s water. Water also exists in the air as water vapor, in rivers and lakes, in ice caps and glaciers, in the ground as soil moisture and in aquifers, and even in you and your dog.” Thus, it is easy to understand why so much heat is stored in water and why water is the prime mover of latent heat energy on the earth..
We cannot create or destroy matter and we are dependent upon the sun, directly or indirectly, as our source of energy for all of our needs. We can capture and store energy, but each time we use energy or store it for later we are left with it in a lower, less useable form.
What happens to energy that hits the earth’s surface and is taken up by plants?
In 1942, a graduate student named Raymond Lindeman did a study on the fate of energy in Cedar Bog Lake in Minnesota.
Figure 2-7: Food Cycle Relationships in Cedar Bog Lake
A bog is a relatively productive ecosystem, meaning it has a greater than average take-up and conversion of energy.
That said, out of 118, 000 gcal/cm2/yr which hit the surface of Cedar Bog, only 111 were taken up by this system. That is approximately .001% of the energy that landed on the bog and was actually taken up by the plants.
That relatively little amount of energy supports the whole ecosystem.
One of the most productive ecosystems in the world is powered by converting 1/100 of a percent of the energy which lands on its surface into energy for all the life which that ecosystem supports. Once converted from sunlight to glucose, nature marshalls the available energy at a better efficiency.
As a general rule, about 10% of the energy taken up by plants through photosynthesis is passed to herbivores, and only about 10% of that (one percent) ends up in the stomachs of carnivores.
This informs us that most of the energy that falls on the surface of an ecosystem is not used by that ecosystem and that living systems function at what humans would refer to as relatively low efficiency. Even though 10% is a low efficiency by human standards, the constant supply of solar energy averaging 240 W/m3 is more than enough to provide energy to all life on the planet.
Figure 2-8 Food Chain ( Drawing By Heather Reed)
Figure 2-9 Representation of Energy and Population in a Food Chain
Humans and Natural Systems
It has been said, “The devil is in the details”. In the case of energy and resources (i.e., matter which is useful to humans), the important details lie in how humans use them.
All living systems have evolved using the finite matter available on Earth. All the chemicals contained in saliva, tears, adrenaline, cells, tissues, organs, and hormones come from earthly materials. There are, mathematically, many more possibilities for the ordering of atoms into more complex chemicals than have actually been made by nature. When chemicals evolve to provide a competitive advantage to the organism, they are conserved. When they are not an advantage, they are discarded.
An important characteristic of natural systems is that all material used on the earth is recycled, so anything built up by nature co-evolved with another process to break it down.
Since recycling material means the movement of matter, this must be accomplished with energy. Indeed, the constant input of solar energy is the source of the movement of matter. Solar energy fuels the assembly of atoms into the complex molecules that are used by living things, as well as the subsequent breakdown of those molecules back to their original components.
All matter built by nature is broken down by nature. Like a great Lego® set, matter is put together in many ways by nature and, in time, that which was built up is taken apart by nature. Thus, the atoms in your body have been around the earth since its creation.
But what happens when humans put things together in ways that have never evolved in nature, and have no natural means of being broken down?
Take plastics, for example, which some have said will be the fossil remains of our civilization. Another example is pesticides.
“A novel substance is either isolated or synthesized every 2.6 seconds on the average during the past 12 months, day and night, seven days a week in the world,” …..”The rate new chemicals are being produced and isolated is astounding. It took 33 years to get the first 10 million chemicals registered and a mere nine months to get the last 10 million chemicals into the database.”
Few, if any, of these newly created substances have been adequately tested in isolation, and certainly not in the billions of possible combinations for their long-term effects on the environment.
Humans depend on continuously digging up matter, using it, and discarding it. Out of sight, out of mind. And, indeed, we must be a bit out of our minds, or just not thinking, if we believe this is a sustainable way of continuing human existence. Because most of these newly created chemicals do not have a natural decomposer to break them down, they persist.
“Plastic first became widespread in the mid-20th century. Since then, about six billion tons have been manufactured. Much of that has ended up as trash, and nobody knows what will become of it…….
Many scientists believe the planet has entered a new geological era, the Anthropocene, in which human activity is leaving a vast and durable imprint on the natural world. Along with building materials, tools and atmospheric signatures, plastiglomerates could be future markers of humanity’s time on earth……
Plastics and plastiglomerates might well survive as future fossils, If they are buried within the strata, I don’t see why they can’t persist in some form for millions of years.”
Plastic is a material made from oil. The amount of plastic we make and use increases every year, as has the world’s consumption of fossil fuels.
What happens to a finite resource when humans demand more and more of that resource? That will be the topic of next week’s blog discussing Chapter Three!