Ok, first off Dip, the Gaia hypothesis is a concept which intends to explain how life could have persisted on this planet for more than 3.5 billion years. Since its formulation in 1979, it has greatly evolved, to the point that it represents justified interests to the scientific community of geosciences, because it makes of life a geological force.
You know how we consider other planets, like mars, to be "dead" ? Well mars is somekind of "aborted" planet, it has the mark of the beginning of a tectonic plate movement, one huge rift, but it didn't go any further. On the opposite, Earth has many tectonic plates which are in constant movement, without which biological life could never have seen the day.
Now, at this point, if you don't agree, at least poetically, that Earth is "alive", then... you lack poetic inspiration and i don't know what to tell you. But if you want to get all scientific about, FINE! 
What has been scientifically proven, is that there is some kind of homeostasis maintained on this planet, which results in relatively constant conditions. Indeed, we could say that throughout Earth's history, the inner dynamism of the planet and the photosynthesis have "unified" into some kind of geochemical planetary battery necessary for biological activity.
Here's how Lovelock defined Gaia; a complex entity involving the Earth's biosphere, atmosphere, oceans, and soil; the totality constituting a feedback or cybernetic system which seeks an optimal physical and chemical environment for life on this planet.
The important point here is that the Earth acts like a giant single system consisting of physical, chemical, geological and biological forces that interact to maintain a unified balance in order to create a prosperous environment to the development of life.
You were asking what today's scientists are working on that has to do with questions raised by the Gaia hypothesis. Well, here is potential evidence that living organisms and Earth interact with each other: (from New Times )
Quote: In normal conditions, the environment is able to regulate itself.? It works as a system.? It has the ability to regulate itself but within certain limits (homeostasis).? For example, the earth is able to regulate the temperature.? One means by which global temperature is regulated is by clouds.? If there are more clouds, more sunlight is reflected away from the earth and the earth cools.? If there are fewer clouds, more sunlight is able to reach the surface of the earth and the earth warms. There are many factors that affect cloud cover over the planet.? The interaction of the atmosphere with the ocean is one major factor.? The oceans cover two-thirds of the earth?s surface.? So, anything that contributes to the formation of clouds over the ocean will have a major impact on the earth?s temperature. According to Dr. Muwanika, lecturer at Makerere University, in the last couple of decades, scientists discovered that for the clouds to form there is need for Cloud Condensation Nuclei (CCN?s) by marine phytoplankton, particularly coccolithophorids.? Clouds form when water vapour in the atmosphere condenses or freezes.? This calls for the presence of Cloud Condensation Nuclei, tiny particles in the atmosphere that lead to the formation of clouds.? Water vapour condenses around these particles.? One substance that can act as CCN is dimethyl surfide (DMS). It has been known that certain algae or phytoplankton (plant plankton that live in the ocean) release trace quantities of DMS. Production of DMS by phytoplankton may be sufficient to cause the formation of clouds.? This should make us pause and think of how living organisms and the earth itself may interact with each other. The role of the phytoplankton (single-celled marine plants) in the formation of rain should make us review our ways of looking at the environment and its components, together with the close relationship between us and all the living and the non-living.? We need to keep all forms of life (biodiversity).? In the environment, everything has its value whether known or not.? We need to protect components of the environment regardless of whether they are big or small, liked or not.
Pretty cool huh? Single-celled plants in the sea have their fingers on earth's thermostat!
And this just gives us an idea of how the whole Earth - the lithosphere, atmosphere, hydrosphere, and biosphere - works together in a harmonious fashion. Its only the tip of the iceberg.
I could give you many more examples of this type of phenomena, inlcuding one I learned about today, concerning ecosystems called lakes, where the effect that wind has on them is essential to the correct distrbution of nutrients and oxygen throughout the entire lake. That's physical forces creating optimal conditions for development of life!
Quote: Diploid said: It's made up junk.

This isn't the dominant feeling in the scientific community. The original Gaia hypothesis has seen a transformation into multiple hypothesis, which is usually a sign that there's lots of work being done on it and that it has some enriching potential. There's the weak Gaia hypothesis, the moderate, and the strong Gaia hypothesis. Most favored is the weak one, and it is the most responsible for the stimulation of continued research on Gaia. It pretty much says everything I stated above concerning the homeostasis on earth.
If you want to learn more about these different hypothesis, check this website out:
http://www.kheper.net/topics/Gaia/Gaia.htm
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