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
Other Resources
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Environment and Life
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Environment and Life

In the late 1970's, Elso Barghoom of Harvard University was looking for the earliest evidence of life, and found it eventually in Swaziland, Africa. He found evidence of bacteria in 3.4 billion year old fossils. This means that life started very early on our 4.5 billion year old planet. The time it took to move from inanimate matter to the first forms of life was actually shorter than that to move from bacteria to larger organisms--the earliest of which appear to be only 570 million years old, as evidenced by hard-shelled fossils of that age that appear all over the Earth.

Early life then probably came from mixtures of materials combining to form biomolecules with the energy provided by ultraviolet light and lightning. Replication of DNA and mutation in rapidly dividing bacteria, as well as local variations in environment, then provided a route to diverse populations of bacteria. Development of metabolic pathways to store and convert energy--mechanisms of fermentation to break down sugars--was an early step. Along the way the bacteria also began to capture atmospheric nitrogen to begin the manufacture of amino acids and other organic compounds. To this day, we need bacteria to take the stable nitrogen gas N2 from the atmosphere and convert it into usable compounds. This "nitrogen-fixing" is discussed under the nitrogen cycle in the Materials System.

Margulis and Sagan also state that "the evolution of photosynthesis is undoubtedly the most important single innovation in the history of life on the planet" (p. 78). The first photosynthetic organisms were bacteria that used H2S rather than H2O. H2S must have been plentiful, emitted from volcanoes. The development of the successive stages of bacterial development is fascinating as described by Margulis and Sagan. Early adaptations included developing pigments to protect against ultraviolet, then top layers protecting the layers below and developing repair enzymes. Repair enzymes persist in us today. When ultraviolet or other ionizing radiation damages part of our DNA, these enzymes remove the damaged portion and replace it with new healthy DNA. Despite the fact that we have had an ozone layer to filter out the almost all ultraviolet for over 2 billion years now, we still have this repair system.

Xeroderma pigmentosum is a rare genetic defect inhibiting DNA repair mechanisms against ultraviolet radiation damage. It is characterized by severe sensitivity to all sources of UV radiation (especially sunlight), and often results in cutaneous lesions, premature aging of the skin, cataracts, increased risk of ocular benign and malign tumors, and sometimes neurological disorders such as mental retardation. To learn more about XP, visit the Xeroderma Pigmentosum Society, or read its disease description at the Atlas of Genetics and Cytogenetics in Oncology and Haematology.

Gaia: Co-Evolution of Climate and Life

Gaia is the Greek goddess of the Earth. While designing experiments for NASA to detect life on Mars, the atmospheric chemist James Lovelock developed the theory called Gaia. Gaia refers to the system of all life on Earth and the atmosphere which mutually regulates prevailing conditions to continue life on Earth. (Did you want the notes on atmosphere of Mars, etc., to be moved here? or did you want them where they are?)

(Note: the name Gaia was suggested to Lovelock at his request by his neighbor, William Golding, author of Lord of the Flies.)

The Gaia hypothesis states that the biota (group of all living organisms) regulate the temperature and gas composition of the atmosphere. Lovelock came to this conclusion because the 20-80 composition of O2- N2 in our atmosphere can not be explained by laws of physics and chemistry alone. If we were to make a simple mixture of these gases in the laboratory along with some of the other materials on Earth, the gases would react quickly and become compounds, and not remain as O2 and N2 in the gaseous state. Lovelock therefore postulated that this unlikely mixture must be aided by the continuous production of these gases by live organisms! If this were not true, our atmosphere would be a mixture of N2, NH3, SOx, CH4, methyl chloride (CH2Cl), and others. These are indeed present but only in minute quantities.

In addition, the Earth's average temperature has remained relatively stable (around 22° C) despite the increase in the sun's temperature over the past 4 billion years. This too has been attributed by Lovelock to the feedback effects of life on the atmosphere.

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Several scientists disagree with Lovelock's hypothesis. Lovelock has actually modeled a simple system, "Daisy World," a planet with black and white daisies circling a sun-like star. He and his co-author, Andrew Watson, have demonstrated the Gaia-like character of this world. The daisies act as thermostats, stabilizing the temperature. In our world, microbes can play the role of the daisies. Margulis and Sagan cite the discovery that about 20,000 years ago there was only two-thirds the amount of CO2 that we have now, and that the rise of CO2 to pre-industrial levels took place abruptly in a 100 year span. This cannot be explained by geophysical or chemical processes alone, but could be the result of a sudden species death of algae.

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  ©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.