Describe the organism that scientists believe was responsible for changing the composition of the early atmosphere. what is it called and how did it change the atmosphere? why was this change to the atmosphere so important?

The early atmosphere was probably mostly carbon dioxide, with little or no oxygen. The proportion of oxygen went up because of photosynthesis. The photosynthesis was conducted from tiny organisms.
cyanobacteria, or blue-green algae. 
They used sunshine, water and carbon dioxide to produce carbohydrates and, yes, oxygen. This change to the atmosphere was very important because the breathable air we enjoy today was created.

Firstly, the water in the dams hold gravitational potential energy as they are above ground level. the gravitational potential energy is then transferred to kinetic energy as it falls, spinning the turbinethe turbine then spins the generator, which is a large magnet surrounded by metal coils. by doing this, the generator generates electricity. in this action, the energy transfer taken place is kinetic to electric energy

It will appear as o2(g) as a reactant