INFORMATION SHEET 2-1

The universe consists of billions of billions of stars and probably an even larger number of associated planets. Our Earth is one particular planet, located within a seemingly ordinary solar system, which consists of the Sun, eight planets, three “dwarf” planets, and additional orbiting bodies, such as asteroids and comets.

Earth is the third closest planet to the sun, orbiting that medium-sized star every 365 days at an average distance of 149 million kilometres, and revolving on its own axis every 24 hours. Earth is a spherical body with a diameter of 12,700 kilometres. About 70% of its surface is covered with liquid water, and the remaining terrestrial area of exposed land and rock is covered mostly with vegetation. With so much of its surface covered with water, one might wonder why our planet was not named “Water” instead of “Earth.”

Earth has a wide variety of ecosystems that maintain its function and make it wondrous. While most of us are familiar with the term “ ecosystem ”

An ecosystem consists of communities of interacting species and the physical environment on which they depend. Although it is well accepted that Earth consists of many different ecosystems, human societies much less readily recognize that Earth itself is an ecosystem, dependent on interacting species and consisting of finite resources. As the human population has grown and increasingly dominated available resources, “ecosystem Earth” has begun to show increasing signs of stress. Loss of biodiversity, environmental degradation, and conflict over resources among the dominant species are typical signs that a biological system is nearing a state change, which could range from collapse of the dominant species, to development of alternative biological communities, to collapse of the entire system. In this special issue, we identify our impacts on ecosystem Earth, seek to understand the barriers to change, and explore potential solutions. Decades of research on ecosystem dynamics can help to guide our thinking about a sustainable future. Bottom-up reductions in human population growth and resource consumption, changes to how we think about our place in the system, and a willingness to prioritize persistence of the other species within our biological community will lead to a healthier planetary ecosystem. It is essential that humanity begins to better appreciate our role as just one part of a large and interdependent biological community. Our ability to dominate the planet's resources makes us directly responsible for determining the future of the ecosystem on which we, and all other forms of life, depend.

The most singularly exceptional characteristic of Earth is the fact that certain qualities of its environment have led to the genesis and subsequent evolution of organisms and ecosystems. These favorable environmental factors include aspects of Earth’s chemistry, surface temperature, and strength of gravity.

Aside from the musings of science fiction, Earth is celebrated as the only place in the universe that is known to sustain life and its associated ecological processes. Of course, this observation simply reflects our present state of knowledge. We do not actually know that organisms do not exist elsewhere – only that life or its signals have not yet been discovered anywhere else in the universe. In fact, many scientists believe that because of the extraordinary diversity of environments that must exist among the innumerable planets of the multitudinous solar systems of the universe, it is likely that life forms have developed elsewhere. Nevertheless, the fact remains that Earth is the only planet definitely known to support organisms and ecosystems. This makes Earth an extraordinarily special place. We can consider the universe at various hierarchical levels (Figure 1.2). The scale ranges from the extremely small, such as subatomic particles and photons, to the fantastically large, such as galaxies and, ultimately, the universe.

Life on Earth occupies intermediate levels of this hierarchy. The realm of ecology encompasses the following levels:

1. individual organisms, which are living entities that are genetically and physically discrete

2. populations, or individuals of the same species that occur together in time and space

3. communities, or populations of various species, also co-occurring at the same time and place

4. landscapes and seascapes (collectively, these are ecoscapes), which are spatial integrations of various communities over large areas

5. and the biosphere in its entirety, which is composed of all life and ecosystems on Earth

NOTE: Take Quiz 2-1 before proceeding to next lesson.