HOW TO FIND ALIENS: PHOTOSYNTHESIS

Scientists have a new method for determining if there are Earth-like planets in the galaxy.  If they find photosynthesis , they might find life.
The search for life on other worlds is generally divided into two camps:   NASA and the European Space Agency (ESA)and their  search for biochemical signs of simple life and SETI (Search for Extra-Terrestrial Intelligence) and their  search for intelligence by listening to radio waves for signals by advanced aliens (highly unlikely).
Futurologist James Lovelock originally proposed that scientists look at the chemistry of a planet to determine whether there is life or not.  Without life a planet moves to chemical equilibrium as on Mars or Venus – dead rocks with no changes to atmospheric chemistry.   Life, however, changes a planet.  When seeking where life might evolve, scientists often focus on the habitable zones around stars, where the heat from the star makes it perfect for liquid water to exist on the surface of a planet.  The reasoning:  if there is water, there could be life.
But now, they are also looking at photosynthesis. When Earth was first formed, it breathed methane and carbon dioxide, while oxygen was rare. But as photosynthesis evolved oxygen was produced in large quantities and changed the planet.
Physicist Werner von Bloh at the Potsdam Institute for Climate Impact Research in Germany suggests that scientists focus on determining where photosynthesis might be possible, since nearly all life on Earth depends on it one way or another for energy.  Although primitive life can exist without photosynthesis, it is necessary for more multi-cellular organisms to emerge.  This is because the main source for oxygen on Earth comes from photosynthetic life and is necessary for any life form to emerge.
To find if photosynthesis exists on a planet, scientists are looking at the light spectrum reflected from the atmosphere of the planet. Different molecules absorb electromagnetic radiation at specific wavelengths. Carbon dioxide and water give strong signals, as does ozone, which is what oxygen is converted to in the atmosphere. Images of reflected light with the presence of oxygen inferred by the spectrum would be considered indicative of photosynthetic life and worth a closer look.
To find  photosynthesis-sustaining habitable zones around stars, researchers are concentrating on where the global average surface temperature of a world stays between the freezing and boiling points of water (0 to 100 degrees Celsius).  Also, when analyzing worlds for their photosynthetic sustainability, looking at their stars is also key.  Stars grow in luminosity as they age, destroying some photosynthesis-sustaining zones while potentially creating others.
Here’s a general description of photosynthesis:
[youtube= http://www.youtube.com/watch?v=hj_WKgnL6MI]