Ecological Structures
Life and the Earth's Environment
What is Life?
Materials for Life
Capturing Energy for Life
Evolution & the Environment
Disruptive Forces on Ecosystems
Measurement of Impact on Ecosystems
Sustainability & Ecological Integrity
Approaches to the Natural Environment
Global and Regional Scales
Global Agreements
Philosophies for Sustainability
Internet Links
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Life and the Earth's Environment
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Life and the Earth's Environment

"But nature is a stranger yet;
The ones that cite her most
Have never passed her haunted house,
Nor simplified her ghost.
To pity those that know her not
Is helped by the regret
That those who know her
Know her less
The nearer they get."
  --Emily Dickinson, cited by Margulis and Sagan in MICROCOSMOS, 1986.

While we can characterize living organisms by various chemical, physical, and biological parameters, the harmony that puts it all together and forms the spark we call life is far from understood. We see live organisms that may be stages toward more complete organisms. Viruses, for example, are essentially a piece of DNA or RNA coated with protein. It is by inserting this unit into cells of other animals that viruses reproduce and continue their lives. Infective viruses have been synthesized from elements. Several scientists have synthesized DNA and RNA molecules that replicate themselves in a test tube. But while we can concoct many of the molecules that must have been in the primeval soup in which life evolved, we cannot yet compose from elements a group of "cells that crawl out of a test-tube" on their own, to paraphrase Margulis and Sagan.

We do know a lot about the environmental conditions that sustain life. We have begun to understand that not only does the environment sustain life, but life in turn has made environmental conditions what they are today. We now discuss some peculiar features and compounds on Earth that make our environment particularly "fit" for our kind of life. Much of this discussion is based on three sources:

  1. Microcosmos: Four Billion Years of Microbial Evolution, by Lynn Margulis and Dorion Sagan, 1986.
  2. Time's Arrow and Evolution, by Harold F. Blum, 1951.
  3. Gaia, by James Lovelock, 1979

Blum discusses the "fitness of the environment," a concept originally proposed by Lawrence J. Henderson in 1913. Certain aspects of the environment make the Earth particularly advantageous for living organisms to live, develop, and evolve. The Earth's size and its distance from the sun (a medium yellow star), and the nature of the sun itself, determine the gravitational force of the Earth and the amount and type of electromagnetic energy we receive. These factors provide the conditions under which life evolved, and that sustain life on Earth.

Exercise / Discussion Questions:

1. List and draw a concept map of how Earth's gravity, its distance from the sun, and the properties of sunlight affect factors critical to a system of living organisms based on carbon, hydrogen, and oxygen.

2. List the characteristics of a "live" system. Which of these are not attainable by artificially-created systems like a computer?

3. What do you think we would have to look for on another planet to determine if there are life forms on it similar to ours?

4. Think of some parts of the Earth with an extreme environment (extreme temperatures, pressures, etc.). Do organisms live there?

[Does this go here? Or should it be a notecard on symbiosis?]

Life can adapt to extreme conditions through symbiosis. Photosynthesis is an original adaptive mechanism developed in a species of bacteria called cyanobacteria a billion years before plants evolved. These seem to have eventually partnered with fungus-like organisms to evolve into the cells of plants. The cyanobacteria have now become the part of the plant called chloroplasts which are the photosynthetic organelles of plants! This gives evidence to a symbiotic theory of evolution. A group of bacteria live in animals intestines. Another species live in the seabed seven hundred meters below the surface of the Gulf of Mexico. Bacteria are responsible for nitrogen fixing -- extracting nitrogen from the air and making it into nitrates and NH3, which can then react with water to provide nutrients.



  ©Copyright 2003 Carnegie Mellon University
This material is based upon work supported by the National Science Foundation under Grant Number 9653194. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.