Oxygen was always there,
FREE oxygen was produced by green plants (after they developed chlorophyll),
They freed it from water ... the hydrogen was combined with carbon dioxide to make sugars and the O2 was released.
Oxygen is main gas of earth. If there is no oxygen in the earth all the life in the earth should die.
Mainly by photosythesis that converted the CO2 in the poisonous early atmosphere, into oxygen.
we get oxygen from the trees
Earth's atmosphere, including the oxygen, is bound to Earth by gravity.
There is oxygen and gravitational force on earth but there is no oxygen and gravitational force
About 21% of the Earth's atmosphere is composed of oxygen.
Oxygen makes it human capable of breathing in earth that's why when there is oxygen, there is life.
too high a concentration of oxygen in the atmosphere
No. Oxygen is not believed to have been present in the early years of Earth's history.
Oxygen makes up approximately 21% of the Earth's atmosphere.
About 21 of the Earth's atmosphere is made up of oxygen.
The Earth's atmosphere is composed of about 21% oxygen. This oxygen is crucial for supporting life on Earth through processes like respiration and photosynthesis.