Scientists estimate that the earth formed some 4.6 billion years ago with the first forms of life appearing around 3.5 billion years ago. these first forms of life were simple prokaryotes. later, the first photosynethic organisms resulted in more in the atmosphere. this allowed for more higher level organisms to appear on earth.

Oxygen in the atmosphere nearly 21 % other wise there was no oxygen in the atmosphere

when the first prokaryotic species occurred in the earths  history some .5 to 2 billion years ago oxygen started building up in the atmosphere as O2 was released as by product in photosynthesis reaction

Scientists estimate that the Earth formed some 4.6 billion years ago with the first forms of life appearing around 3.5 billion years ago. These first forms of life were simple prokaryotes. Later, the first photosynethic organisms resulted in more oxygen in the atmosphere. This allowed for more higher level organisms to appear on Earth.

Explanation:

The primitive atmosphere was absent of oxygen. The photosynthetic organisms were the ones who gave their origin. These organisms are cyanobacteria that are photosynthetic and prokaryotic. They organize photosynthesis from the breakdown of water molecules. Thus during millions of years molecular oxygen was increasing its concentration until it changed its character from reductant to oxidant.

did you mean: energy is defined ashyperactivitya caloric measurementthe ability to move matterthe ability to think and analyze this form of energy is called "energy in motion" or "energy of moving matter"potential energy kinetic energy electrical energy1 ptlights on a stage can be examples of all of the following forms of energy exceptelectrical energylight energythermal energysound energywhen one type of energy changes to another this is called energy energy is stored based on their position or shape this is called energy.kinetic potential sound electromagnetic

mammal

explanation: