Atmospheric Structure and Ozone

Solution:- (A) Global warming

A greenhouse gas (sometimes abbreviated GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. 

Cyanobacteria also known as Cyanophyta, are a phylum of bacteria that obtain their energy through photosynthesis, and are the only photosynthetic prokaryotes able to produce oxygen. The name "cyanobacteria" comes from the color of the bacteria. Cyanobacteria, which are prokaryotes, are also called "blue-green algae", though the term "algae" in modern usage is restricted to eukaryotes. Phototrophic eukaryotes perform photosynthesis by plastids that may have their ancestry in cyanobacteria, acquired long ago via a process called endosymbiosis. These endosymbiotic cyanobacteria in eukaryotes may have evolved or differentiated into specialized organelles such as chloroplasts, etioplasts and leucoplasts. By producing and releasing oxygen (as a byproduct of photosynthesis), cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere into an oxidizing one, causing the Great Oxygenation Event and the "rusting of the Earth", which dramatically changed the composition of the Earth's life forms and led to the near-extinction of anaerobic organisms.

The Ozone layer is located in the stratosphere in a region that is 10 to 50 km above the Earth.

The atmosphere is divided into layers separated by transition zones called pauses. The stratopause is the boundary layer that separates the stratosphere from the mesosphere above it.

The ozone layer filters out most of the sun's harmful ultraviolet radiation and is thereby significant for the life on Earth.

Ozone in the troposphere is considered a pollutant. Its background concentration is typically very low, generally around 0.05 ppm in clean air environments.

The troposphere is the lowest layer of Earth's atmosphere. It is the layer closest to the ground where weather phenomena occur.

The ozone layer is present in the stratosphere above the Earth. The layer is present at a distance of about 20-30 km away from the surface of the Earth. The layer of ozone is responsible for the absorption of the harmful Ultraviolet radiations from the solar radiations. These radiations are prevented from entering the Earth's atmosphere to prevent the development of skin cancer

• The ozone layer or ozone shield is a region of Earth's stratosphere which contains a high concentration of ozone ($O _3$) in relation to other parts of the atmosphere,
  
• The ozone layer acts as a filter for the shorter wavelength and highly hazardous ultraviolet radiation (UVR) from the sun, protecting life on Earth from its potentially harmful effects.
• Hence Ozone shields the earth from the harmful ultraviolet rays from the sun.
• So, the correct answer is 'Sun'.

In the stratosphere, ozone molecules (three oxygen atoms) bonded together, prevent some of the Sun's most intense rays from reaching the Earth's surface. Currently, scientists and researchers worldwide are monitoring this layer; so thin at the South Pole, we call it a hole where the molecules are being very less.

Air is a bad conductor of heat and not a good conductor hence the temperature on the earth is maintained for life to exist unlike the other planets. Atmosphere prevents sudden increase in temperature during the day light hours. It slows down the escape of heat into outer space during the night.