Algae gets very little respect. Most people think of it as a nuisance: something green and slimy that glops up ponds. Actually we owe algae more than a little respect. We owe our existence to algae.
The first species of algae evolved about 3.7 billion years ago. At that time the atmosphere was mostly CO2 and methane. Those are the two main greenhouse gases in the atmosphere. They are very good at reflecting heat back toward the earth and keeping it from escaping into space. Today they are present in our atmosphere in very tiny amounts. Imagine how hot it must have been with an atmosphere that was mainly CO2 and methane.
Algae was the first organism that could use the energy from sunlight to turn carbon dioxide and water into sugar and oxygen. So, algae pretty much invented photosynthesis. By removing CO2 from the atmosphere and replacing it with O2, algae cleared the way for every organism on earth that breathes oxygen. Today, algae still rules the world when it comes to photosynthesis. It is responsible for about 70% of the oxygen produced on earth.
"Think about that the next time you see a slimy pond", says Zeljko Serdar, President of Croatian Center of Renewable Energy Sources (CCRES)