The correct answer is - ozone.
The ozone is essentially three molecules of oxygen, or O³. This gas is crucial for the life on the Earth because it is the one that manages to filter out big portion of the UV radiation from the Sun which is extremely harmful if its too strong, as it will contribute to the dying out of pretty much every living organism.
While the ozone layer in the stratosphere is very useful, the ozone in the lower parts of the troposphere is actually considered as pollutant. The reason why it is considered as pollutant is because it is very harmful if inhaled, and it also heavily damages the plants.
Answer:
The Hadean eon represents the time interval between 4.6 billion to 4 billion years back. It is marked by the initial formation of the earth , right from the time of gathering and accumulation of interstellar dust particles and gases, and there was frequent collision between the planetesimals of relatively larger in size. The core and the crust formed and started to become stable and also gradually led to the formation and expansion of the ocean and the earth's atmosphere.
This is how the earth gradually started to form and develop and took the shape during the time interval between 4.6 billion to 4.2 billion years old, and where the oldest rocks found on earth is dated from about 4.2 billion years in the past.
