Please, help me to answer this question

Omar,

My gut feeling is that it would take at least decades for the
atmosphere to become unbreatheable by humans. A far more pressing
issue would be mass starvation: photosynthetic life is the base of all
food chain in the surface of Earth. (I stress "surface of the Earth"
because there are chemiosynthetic food chains in the bottom of the
ocean that are completely independent from sunlight.) So all animal
life in the surface would be dead in a few years.

However, a pathogen that is able to destroy all photosynthetic life is
*extremely* unlikely - impossible, I would say. But I think that you
already know that and is just proposing a though experiment. ;-)

On 7/3/05, Omar E. Vega wrote: