Ecology is the investigation of the interactions between living things and their environment. Ecologists must use mathematical models and computer simulations because these approaches allow them to study the interactions of variables and simulate large-scale experiments.

The environment, that region of the earth where life can secure a foothold, is called the biosphere.

The tenacity of living things and their ability to colonize even the harshest of environments has surprised the scientific community.

The physical characteristics of the biosphere

The physical characteristics (abiotic factors) of the biosphere necessary for life include:


  1. Presence of water in its liquid state. (see previous lecture about water) About 70% of the earth is covered with water. The largest biome is marine, the salty environment of the oceans where life first arose and diversified.


  1. A gaseous atmosphere. Living things do not need to be in physical contact with the atmosphere proper. Nevertheless the atmosphere is essential for the existence of life because it filters out harmful radiation and helps maintain a moderate climate. Gases in the atmosphere also supply the necessary ingredients for many of life's metabolic processes. (Oxygen for respiration, Carbon dioxide and water vapor for photosynthesis, and nitrogen for amino acids and nucleotides.)

    Today's atmosphere contains 79% nitrogen, 20% oxygen. The remaining 1% contains argon, carbon dioxide, and a variety of other gases. The early atmosphere of the earth had little or no oxygen.


  1. A spinning earth on a tilted axis. The earth's tilt of 23° gives us the 4 seasons. While the southern hemisphere is experiencing the direct summer rays of sunlight, the northern climes receive only a glancing stream of light and shorter days. 180 degrees of rotation later (183 days), when the earth is on the other side of the sun, each hemisphere experiences the opposite season.


  1. Light from the sun provides most of the energy for life. (Some energy comes from radioactive decay deep inside the earth.) Although only 1% of sunlight reaching the surface of the earth is captured in photosynthesis it accounts for well over 99% of energy using by living things.

    Light is also essential to the hydrologic cycle, the continuous movement of water from the liquid state in bodies of fresh and salt water to the clouds and vapors found in the atmosphere.



Links to Other Lectures

Want to go on a Web Quest in search of Biomes?


Modified July 10, 2005