Analysing The Gaia Theory Engineering Essay

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The study of astrobiology is partly based on facts of life on Earth since this is the only planet known to contain life.

The '''''Gaia Hypothesis''''', most simply expressed "''The Earth Is Alive''", describes the Earth as one living organism with the biosphere acting to maintain the conditions to sustain life on Earth this, along with the evolution of life, makes the Earth a complex, evolving system out of equilibrium with its surroundings. Not dissimilar to the definition of life.

The Gaia Hypothesis was first proposed by [http://en.wikipedia.org/wiki/James_Lovelock James Lovelock], and co-author [http://en.wikipedia.org/wiki/Lynn_Margulis Lynn Margulis], in the late 1960's and has been backed up by experimental evidence since, so it is now known as the Gaia theory. Lovelock also proposed that any other planet with life should be easy to find by studying the spectra of the atmosphere for volatiles, such as water or ozone.

==Synopsis==

The Gaia theory describes the Earth as a single, complex system in which the biosphere, the atmosphere, the oceans and the soil all are tightly linked in an evolving system. This system is called Gaia (after the Greek goddess of the Earth [http://en.wikipedia.org/wiki/Gaia_(mythology)]) and is there to maintain and physical and chemical environment optimal for life.

The Gaia system is due to the unconscious feedback of the biological beings of the Earth, leading to a stabilization of the conditions important for life; surface temperature, atmospheric composition and ocean salinity.

===Surface Temperature===

The Sun's intensity has increased 25-30% since life began on Earth, yet the surface temperature has remained constant.

At the moment this temperature is being increased by human influence on the composition of the atmosphere, mainly the CO<sub>2</sub> concentration, which Lovelock says will lead to accelerated global warming and mass human mortality [http://en.wikipedia.org/wiki/James_Lovelock#Climate_and_mass_human_mortality].

====Daisyworld====

[[Image:Daisy.gif|thumb|right|Plots from a Daisyworld simulation where the world is populated by black & white daisies.]]

Daisyworld is a mathematical model of a planets energy budget, developed by James Lovelock and [http://en.wikipedia.org/wiki/Andrew_Watson_(scientist) Andrew Watson]. It models a planet populated by two different types of plant, black and white daisies, and the influence they have on the albedo of the planet. Black daisies will absorb light whereas white daisies will reflect light, so the model is based on the competition of growth due to temperature variance, finding that the populations balance out at a temperature where both types of daisy will grow at their optimum.

===Atmospheric Composition===

Atmospheric composition has remained pretty constant over the time there has been life on Earth, all the gases in the atmosphere, except noble gases, have to be produced by organisms or at least processed by them.

Oxygen is the second most reactive element after fluorine, so should react with other gases and minerals in the atmosphere or in the crust. Oxygen is also an element essential for life, life requires the element in fairly constant conditions.

Also methane, which is produced in quite large amounts, should not exist naturally as it will combine with oxygen in the atmosphere.

A sample of dry air would typically contain 78% N<sub>2</sub>, 21% O<sub>2</sub> and the other 1% is made up of elements such as CO<sub>2</sub>, CH<sub>4</sub> (Methane), N<sub>2</sub>O (Nitrous Oxide), NH<sub>3</sub> (Ammonia) and a few other elements. [http://www.gaianvariations.com/learn/ep42.htm]

===Ocean Salinity===

The [http://en.wikipedia.org/wiki/Salinity salinity] of the oceans has been around 3.4% for a very long time. This salinity is important as most living cells need constant salinity and won't take levels above about 5%. How the salinity has remained constant has been a mystery, because river salts should have raised the salinity a lot higher than 3.4%. This constant salinity can only really be explained through the influence of biology.

===CO<sub>2</sub>===

The carbon cycle is seen as one of the complex processes for maintaining life. The main natural source of carbon dioxide in the atmosphere is due to volcanic activity, and the only natural sink for carbon dioxide is in the formation of [http://en.wikipedia.org/wiki/Carbonate_rocks carbonate rocks].

==Hypothesis becomes Theory==

To start with James Lovelock called the concept of a living earth, or Gaia, a hypothesis, but nowadays it is referred to as the Gaia theory, due to successful experiments on some of the predictions of the hypothesis.

{| class="wikitable" border="1"

|+ Predictions, tests and results relative to the Gaia theory.

(Source: Lovelock, James.''The Vanishing Face of Gaia''. Basic Books, 2009, p. 177. ISBN 978-0-465-01549-8)

|-

! scope="col" | Prediction

! scope="col" | Test

! scope="col" | Result

|-

| Mars is lifeless (1988) || Atmospheric compositional evidence shows lack of disequilibrium || Strong confirmation, Viking mission 1975

|-

| That elements are transferred from ocean to land by biogenic gases (1971) || Search for oceanic sources of dimethyl sulphide and methyl iodide || Found 1973

|-

| Climate regulation through biologically enhanced rock weathering (1973) || Analysis of ice-core data linking temperature and CO<sub>2</sub> abundance || Confirmed 2008, by Zeebe and Caldeira

|-

| That Gaia is aged and is not far from the end of its lifespan (1982) || Calculation based on generally accepted solar evolution || Generally accepted

|-

| Climate regulation through cloud albedo control linked to algal gas emissions (1987) || Many tests have been made but the excess of pollution interferes || Probable for southern hemisphere

|-

| Oxygen has not varied by more than 5 percent from 21 percent for the past 200 million years (1974) || Ice-core and sedimentary analysis || Confirmed for up to 1 million years ago

|-

| Boreal and tropical forests are part of global climate regulation || Models and direct observation || Generally accepted

|-

| Biodiversity a necessary part of climate regulation || By models but not yet in the natural ecosystems || Jury still out

|-

| The current interglacial is an example of systems failure in a physiological sense (1994) || By models only || Undecided

|-

| The biological transfer of selenium from the ocean to the land as dimethyl selenide || Direct measurements || Confirmed 2000, Liss

|}

==Analysis of the theory==

The Gaia hypothesis was largely ignored by many scientists, between 1969 and 1977. Most scientists saw the Gaia hypothesis as some kind of [http://en.wikipedia.org/wiki/New_Age new age] [http://en.wikipedia.org/wiki/Religion religion] because it was named after a Greek goddess. Lovelock's book "Gaia, a new look at life on Earth", was criticised for taking a [http://en.wikipedia.org/wiki/Teleology teleological] approach to life, in 1990 Lovelock responded to these criticisms saying "Nowhere in our writings do we express the idea that planetary self-regulation is purposeful, or involves foresight or planning by the biota."

===The Earth is Alive===

A fully formulated [http://en.wikipedia.org/wiki/Life#Definitions definition of life] has not yet been put together leading to the statement in the first paragraph of Lovelock's book, written in 1979, "the quest for Gaia is an attempt to find the largest living creature on Earth," being a controversial statement. This controversy is partly due to the different characteristics and implications given to this hypothetical (statement of) life and also partly due to the simple terminology used by Lovelock is his books.

One of the fundamental concepts of the empirical definition of life is that it has to be born out of [http://en.wikipedia.org/wiki/Natural_selection natural selection] and the life-form also has to have the ability to pass on its genetic code to a different generation. Which some scientists have used as an argument against the Gaia theory.

However, Lovelock defines life as being [http://en.wikipedia.org/wiki/Self-preservation self-preserving], [http://en.wikipedia.org/wiki/Self-similarity self-similar] system - which means life could be called a cell also an organ in a larger organism. This definition of life is known as [http://en.wikipedia.org/wiki/Autopoiesis autopoiesis]. In this definition reproduction becomes an optional process, which supports Gaia, but even Lovelock, in the original Gaia book, states that our biosphere may reproduce when, and if, humankind choose to colonise and terraform another planet.

==Types of Gaia==

[[Image:Lovelock.jpg|200px|thumb|left|James Lovelock in 2005 at age 91]]

There are two extensions to James Lovelock's homeostatic Gaia theory, proposed by [http://en.wikipedia.org/wiki/James_Kirchner James Kirchner] at the first Gaia Chapman conference. One view being the radical Strong Gaia and the other being the incontestable Weak Gaia.

===Strong Gaia===

There are a few types of ''Strong Gaia'' hypotheses, one is called the "Optimizing Gaia" which claims that biological life influence their surroundings to create conditions that are advantageous for themselves, or for life in general. Another hypothesis is called "Omega Gaia" which states that through stages of cosmogenesis (see [http://en.wikipedia.org/wiki/Cosmogony Cosmogony]) the Earth is evolving ; cosmogenesis affecting the [http://en.wikipedia.org/wiki/Geosphere geosphere], [http://en.wikipedia.org/wiki/Biogenesis biogenesis] affecting the [http://en.wikipedia.org/wiki/biosphere biosphere] and [http://en.wikipedia.org/wiki/Noogenesis noogenesis] affecting the [http://en.wikipedia.org/wiki/Noosphere noosphere]. Omega Gaia also says that the universe will reach a point of maximum [http://en.wikipedia.org/wiki/Complexity#Disorganized_complexity_vs._organized_complexity organised complexity], called the ''Omega Point''. An extension to this hypothesis is that the Gaia theory applies to galaxies, "The question is not whether there is life outside our planet, but whether it is possible to have ''nonlife''," said by [http://en.wikipedia.org/wiki/Guy_Murchie Guy Murchie], who proposed this extension to the hypothesis.

===Weak Gaia===

The presence of biological life on the Earth has altered how the atmosphere is, is the basis of the weak Gaian hypothesis, however it can be said that the Earth's atmosphere is self-organising in order to maintain life. The weakest form of the weak Gaian hypothesis is just that the biological life on Earth influences the non-living life (or [http://en.wikipedia.org/wiki/Abiotic abiotic]), this is known as [http://en.wikipedia.org/wiki/Co-evolution co-evolution]; one system evolves because of the evolution of a closely related system. The weak hypotheses are more acceptable to many scientists because they assume that the Earth isn't a living being, they say that the biota and the abiota may influence each other.

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