Shil DasSarma, a microbial geneticist at the University of Maryland, has pointed out that species of archaea use another light-absorbing molecule, retinal, to get power from the green spectrum. Some scientists believe that green-light-absorbing archae were once the most common in the earth environment. This could have left open a "niche" for green organisms which would absorb the other wavelengths of sunlight. This is just a possibility, and Berman wrote that scientists are still not convinced of any one explanation.