• Components
• Processes
• Humans and Their Environment

Most Canadians are aware of the many environmental issues the world faces today. To understand them, however, they must be able to place them in an appropriate social and ecological context. This chapter examines fundamental ecological facts and concepts, including the role of the human species in the biosphere.

Fundamental Facts and Concepts

Earth, the environment, the 'biosphere'... Although these are common terms today, we don't always stop to think about exactly what each of them means. This section explains some of the basic facts and concepts that are necessary to explore our world and our place in it.

Q2.1
What is the Earth, and what makes it unique? The Earth is one of the nine planets in this solar system. What makes it unique is its ability to support life. Temperatures are moderate, the acidity of water is close to neutral, and the various chemical elements necessary for life are present in the right proportions. Conditions on the Earth's nearest neighbours are very different, despite the fact that Venus, the Earth, and Mars are similar in size and in distance from the sun (within a factor of 2 in both cases). Venus is very hot (400oC on average) with a dense, highly acidic atmosphere composed almost entirely of carbon dioxide. Mars is cold, with a thin but also highly acidic, CO2-rich atmosphere. There is water on Mars but only in the form of ice at the poles. The Earth, in contrast, has an atmosphere composed mostly of nitrogen and oxygen, with little CO2. Its surface is covered mostly by water in liquid form. In fact, it was in these areas that life on Earth first began.

Q2.2
Has the Earth changed over time? Yes. The Earth and all of its elements have evolved interactively over the span of billions of years. We often think of nature as constant unless disturbed by human action; the idea of a 'balance of nature' may be understood in this sense. Yet the Earth and its ecosystems are dynamic, not static. Climate, for instance, has varied greatly over the course of the Earth's history. Likewise, the tectonic plates upon which the continents ride are constantly (albeit slowly) in motion. One of the most radical changes our planet has experienced has been the evolution of life, from simple bacteria to complex life forms like birds and mammals.

Q2.3
What do we mean by the 'environment'? Our 'environment' is literally everything that surrounds us. We often take it to refer to just the 'natural' aspect of our surroundings, especially when we speak of 'the environment'. In fact, our environment includes human-built elements such as cities and buildings, not just rocks and trees.

Q2.4
Is the distinction between organisms and their 'environment' absolute? No. Molecules that are part of the non-living environment may later be incorporated into organisms, and will eventually find their way back into the environment. Organisms and their environment are interconnected and interdependent aspects of one world.

Q2.5
What is the biosphere? In its literal sense the 'biosphere' is the part of our planet where life exists. It is a thin band circling the surface of the Earth, stretching from the lower levels of the atmosphere through the top few metres of soil and penetrating to the depths of the oceans. This area is vital for the survival of life since it receives solar energy and contains the solid matter, liquids and gases that are necessary for life.

The biosphere can also be understood as the set of processes that maintain conditions hospitable for life. In this sense, the biosphere is more than just an area it is the Earth's life support system itself.

through photosynthesis by green plants. Likewise, when we metabolize food, the chemical energy in what we eat is converted into thermal energy (heat) and kinetic energy (motion).

Energy

In one form or another, energy is constantly flowing through and around us. This section explains the scientific concept of energy and describes the importance of energy for the biosphere.

Q2.6
What is energy? By 'energy' we mean the ability to induce change (to move something or to heat something, for example). Energy is an inherent characteristic of any physical system; everywhere there is change, there is a transformation of energy. Without energy, life would be impossible.

Q2.7
Are there different sorts of energy? Yes. Scientists speak of energy as being either potential or kinetic. Potential energy is energy that is stored somewhere. A raised ball, for example, has potential energy by virtue of its position relative to the Earth. When the ball is dropped, the potential energy is transformed into kinetic energy. Kinetic energy is energy associated with motion. Similarly, there is potential energy in a piece of wood. When burned, the potential energy present in the chemical bonds of the wood molecules will be converted into heat the kinetic energy associated with the vibration of atoms. Energy is also present in elastic bodies such as compressed springs or gases and in electrical and magnetic fields.

Q2.8
Can energy be created or destroyed? No. It can move from one location to another, but it cannot just disappear, nor can it arise out of nothing. This is known as the law of conservation of energy, or the first law of thermodynamics. There is a fixed amount of energy in the universe.

Q2.9
Can energy change forms? Yes. Energy is in fact constantly being converted from one form to another. For example, solar energy in the form of radiation is converted into chemical energy through photosynthesis by green plants. Likewise, when we metabolize food, the chemical energy in what we eat is converted into thermal energy (heat) and kinetic energy (motion).

Q2.10
What is the primary source of the Earth's energy? The sun is the energy source upon which almost all life depends. The Earth receives energy from the sun in the form of radiation. This energy undergoes many changes, affecting the planet in many ways, and is eventually re-emitted as heat back into space. Virtually all of the energy available at the Earth's surface comes from the sun; a very small amount of heat comes from the Earth's core.

The sun sustained the vegetation and animal life that was fossilized 300 million years ago and has been transformed into oil, natural gas, and coal. The sun continues to be the direct energy source for certain living things (e.g., plants), which pass energy on to other living things (e.g., animals), when eaten. It also drives most of the Earth's natural cycles. This means that hydroelectric energy, for example, derives from the sun.

The sun drives the water cycle. Heat from the sun causes water to evaporate, this vapour collects in clouds, then falls as rain. Rain runs into rivers, which are directed through turbines to produce hydroelectric energy.

Q2.11
What happens to the sun's energy once it reaches the Earth? After travelling about 150 million km the sun's radiation arrives at the outer edges of the Earth's atmosphere. About half of this radiation reaches the Earth's surface; the rest is reflected back into space by clouds, scattered by dust or vapour, or absorbed by the atmosphere and re-radiated. Of the energy that reaches the Earth's surface, some is absorbed by land and oceans, while some is reflected back into the atmosphere and space. The energy that is absorbed is converted into heat, some of which escapes into space, and some of which is trapped by water vapour and other gases in the atmosphere (this is known as the greenhouse effect). Eventually all of the energy the Earth receives from the sun returns to space.

focus

The sun drives the water cycle. Heat from the sun causes water to evaporate; this vapour collects in clouds, then falls as rain. Rain runs into rivers, which are directed through turbines to produce hydroelectric energy.

Q2.12
How do movements of air and water affect the distribution of the solar energy that reaches the Earth? The heat that is generated when the Earth's surface or atmosphere absorbs solar radiation is re-distributed across the globe by movements of air and water in the planet's oceans and atmosphere. This is, in fact, one of the ways in which the biosphere maintains conditions hospitable for life. If incoming solar radiation were exactly balanced in every region by outgoing thermal radiation, few forms of life could endure. Consider that at the equinoxes (March 21 and September 23) the Equator receives the maximum amount of solar radiation, while the poles receive practically none. Without movements of air and water to equalize temperatures, the poles would be far colder than they already are, and the equator much warmer.

Q2.13
What is the role of energy in living organisms? Energy is essential for all life. Life is based upon the conversion, utilization, storage, and transfer of energy. Through photosynthesis, plants convert solar energy into chemical energy used in growth and propagation. Some plants are eaten by animals, which may themselves be eaten by carnivorous animals. At each stage of this process, some of the chemical energy stored in plant or animal tissue is used for growth and propagation, while most of it (more than 90% of it, in fact) is dissipated as heat.

Atmosphere, Hydrosphere, Lithosphere

The atmosphere, hydrosphere, and lithosphere are the 'abiotic' (non-living) components of our planet. This section looks at these components and at the roles they play in the biosphere.

Q2.14
What is the atmosphere? The atmosphere is the whole mass of gases, vapour, and particulates surrounding the Earth. Eighty percent of the atmosphere's mass lies within its lowest layer, the troposphere, which extends to an altitude of between 6 and 17 km above the Earth's surface (depending on the location and the time of the year). The stratosphere above it consists of 19% of the atmosphere, continuing to about 50 km. The remaining 1% extends outward beyond the stratosphere, gradually fading into interplanetary space.

Q2.15
Why is the atmosphere important? The atmosphere performs three functions that are considered to be crucial to the maintenance of life on Earth.

• It acts as a conduit for the transfer of carbon, nitrogen, oxygen, and hydrogen, which are constituents of all living matter. Living things convert these elements into sources of carbohydrates and proteins for nourishment.

• It protects the Earth from visible threats like meteorites, which for the most part burn up as they go through the atmosphere, and from invisible threats like harmful radiation.

• It acts as an insulator for the Earth. Contained within the atmosphere are a series of gases, known as greenhouse gases, that trap heat from solar radiation. This heat warms the Earth so that it can sustain life.

Q2.16
What does the atmosphere consist of? The atmosphere consists mainly of nitrogen and oxygen; these two gases make up 99% of all gases in the atmosphere by volume (excluding water vapour). The diverse gases found in the final one percent are called trace gases.

Q2.17
What are the trace gases, and why are they important? Trace gases include noble gases, carbon dioxide, methane, ozone, sulphur dioxide, nitric oxide, and chlorofluorcarbons (CFCs). Although they make up only a small portion of atmospheric gases, several have great importance.

• Carbon dioxide is a necessary element in the process of photosynthesis which maintains plant life (and indirectly animal life also).

• Some trace gases, including carbon dioxide, help retain heat from the solar radiation that strikes the Earth. These are known as greenhouse gases; they retain the heat necessary to sustain life.

• Stratospheric ozone helps protect organisms from the harmful effects of ultraviolet radiation.

• Some trace gases are pollutants. CFCs contribute to stratospheric ozone depletion; sulphur and nitrogen oxides contribute to smog.

Q2.18
What is the hydrosphere? The hydrosphere includes all the waters of the Earth, in whatever form: solid, liquid, or gas. It includes water in the atmosphere on the Earth's surface, and underground water. Saltwater oceans and seas contain approximately 95% of the Earth's water. Of the remaining 5% that is fresh, almost all of it is either in the form of ice in glaciers and polar ice caps, or underground. Thirty percent of the world's fresh water is tied up in the polar ice caps.

Q2.19
Why is the hydrosphere important? Water is absolutely vital; without it, no organism present on Earth could live. Water makes up a large proportion of each cell in our bodies and is a key element in many body processes; living things constantly need to replenish their water supplies. As well, both freshwater and saltwater provide habitats for aquatic life, adding greatly to the diversity of organisms on the planet. The hydrosphere also plays a major role in the earth's climatic patterns.

Q2.20
What is the lithosphere? This term normally refers to the rocks of the earth. Sometimes it is used to refer to just the uppermost 100 km of soil and solid rock, which is rich in the elements silicon, oxygen, magnesium, and iron.

Q2.21
Why is the lithosphere important? The lithosphere provides the solid surface necessary for terrestrial organisms, but it is much more than just an area on which life can roam. It is also a reservoir of nutrients that are essential for life, accessible to living things in the form of soil. It holds deposits of fresh water and energy resources. Geographic variations of the lithosphere also affect climatic patterns.

Q2.22
What is soil? Soil is a mixture of decomposed rock and organic matter that contains moisture and air, as well as micro- organisms of various types. The Earth's soils contain the water and nutrients necessary to support plant life.

Life

Living organisms have played an important role in the evolution of our planet. This section gives a brief history of life, and describes the different kinds of life that are found on our planet.

Q2.23
When did life on our Planet originate? It is estimated that the first, simplest forms of life bacteria and blue-green algae developed roughly 3.6 billion years ago.

Q2.24
How has life changed since then? Roughly 590 million years ago, organisms with skeletons began to develop. About 160 million years later, life began to move to land. The reign of the dinosaurs started about 248 million years ago, and ended abruptly 65 million years ago. It was at this point that mammals began to flourish. The species 'homo sapiens' is less than 100,000 years old.

Q2.25
Has life had an effect on the environment? Yes. Atmospheric change provides the most dramatic, but certainly not the only example. Two billion years ago, the Earth's atmosphere was very different from today much higher in carbon dioxide, ammonia, methane and hydrogen, and lacking oxygen. We owe our current oxygen-rich atmosphere to early photosynthesizing organisms in the sea, which took in carbon dioxide and gave off oxygen. Without millions of years of photosynthesizing life in the oceans, complex, oxygen-breathing forms of life could never have developed. In fact, life in general would have been impossible on land since without oxygen there is no ozone; without ozone there is little protection against harmful ultraviolet radiation coming from the sun (see the chapter on ozone in section 3).

Q2.26
What are the basic types of organisms? The Earth's species are classified into major groups called 'kingdoms'. Species within one kingdom have similar characteristics. We normally think of two kingdoms of life: plant and animal. Single-celled organisms used to be classified as either plants or animals, depending upon whether they nourished themselves through photosynthesis or by ingesting their food. Recently it has been realized that they do not fit these categories very well, and they have been given their own kingdoms. As well as plants and animals there are monera (such as bacteria and blue-green algae), protista (such as amoeba), and fungi (such as molds and mushrooms).

Q2.27
How do we distinguish between the different kingdoms? The first broad distinction is between single-celled organisms (monera and protista) and multi-celled organisms (plants, animals and fungi). The distinction between the two kingdoms of primitive organisms is that protista have a cell nucleus where their DNA is kept, while the DNA of monera lies around loose. More complex forms of life can be distinguished by the way they nourish themselves. Fungi absorb what they need from their environment, whereas plants produce nutrients by photosynthesis, and animals gain nutrients by consuming plants, fungi, or other animals.

Q2.28
What is a species? A species consists of a group of organisms capable of producing fertile offspring. There are exceptions to this rule, however. It is not always possible to verify whether different organisms are capable of breeding. There are, for example, many thousand different types of beetles; scientists judge whether or not specimens belong to the same species based upon similarities of anatomy, not by attempting to mate beetles. Single-celled organisms are also difficult to classify according to this definition, since they reproduce by splitting cells, not by mating. In this case, 'species' are distinguished by various other characteristics.

Q2.29
What is the most common type of life? Judge by mass, plants account for the vast majority of life on our planet roughly 90% of it, by most estimates. Roughly 250,000 species of plants have been described, compared to (roughly) 4,000 species of mammals, 4,700 species of monera, 47,000 species of fungi, and 750,000 species of insects.