Describe the stages in the formation and evolution of Earth's atmosphere. Where does the ozone in the atmosphere come from, and why is it important?

Short Answer

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The formation and evolution of Earth's atmosphere can be summarized in the following stages: 1) The formation of Earth's first atmosphere, primarily composed of hydrogen and helium; 2) The development of the second atmosphere through volcanic outgassing, rich in gases like nitrogen, water vapor, and carbon dioxide; 3) Gradual changes in the atmosphere due to the emergence of life, especially cyanobacteria, leading to an increase in oxygen levels; 4) The Great Oxygenation Event, marking a drastic rise in oxygen levels and the decline of anaerobic bacteria; 5) Formation of the ozone layer, as ultraviolet light reacts with oxygen molecules prompted by increased oxygen concentrations; and 6) The present Earth's atmosphere, with a composition of 78% nitrogen, 21% oxygen, and trace amounts of other gases. Ozone in the atmosphere is formed through the reaction of ultraviolet light with oxygen molecules, creating an essential layer that absorbs most of the Sun's harmful UV radiation. This ozone layer protects life on Earth from the adverse effects of UV exposure, such as skin cancer, cataracts, and damage to ecosystems.

Step by step solution

01

Formation of Earth's First Atmosphere

The origin of Earth's first atmosphere can be traced back to its formation around 4.6 billion years ago. The atmosphere was primarily composed of hydrogen and helium due to the gravitational pull of the newly formed Earth. However, this original atmosphere was gradually lost to space due to Earth's relatively weak gravitational field.
02

Second Atmosphere and the Role of Volcanic Gases

A new, second atmosphere was created mostly through outgassing from the planet. Volcanic eruptions released gases trapped within the Earth's interior, forming an atmosphere composed mainly of nitrogen, water vapor, carbon dioxide with smaller amounts of sulfur dioxide, carbon monoxide, sulfur, chlorine, and other trace gases.
03

Formation of the Present Atmosphere

Over time, Earth's atmosphere began to dramatically change. This began with the gradual development of life, especially the emergence of cyanobacteria, which used sunlight for photosynthesis. Photosynthesis led to the production of oxygen gas, which gradually accumulated in the atmosphere. However, most of the early oxygen combined with iron and sulfur in the oceans and the Earth's crust, a process known as oxygen sinks.
04

Great Oxygenation Event or Oxygen Revolution

Around 2.4 billion years ago, oxygen levels in the atmosphere increased dramatically during an event known as the Great Oxygenation Event. This increase in oxygen eliminated many forms of anaerobic bacteria, making way for oxygen-breathing life forms to dominate.
05

Formation of the Ozone Layer

With increased levels of oxygen in the atmosphere, conditions arose for the formation of ozone. When high-energy ultraviolet (UV) light from the sun strikes molecules of oxygen, they can be split into individual oxygen atoms. These atoms can then combine with oxygen molecules to form ozone.
06

Importance of Ozone

The ozone layer plays a crucial role in the protection of life on Earth. It absorbs most of the Sun's harmful ultraviolet radiation which can cause skin cancer and cataracts, damage ecosystems like the ocean's phytoplankton, and disrupt DNA of the living cells. It acts as Earth's sunscreen, protecting living organisms from these damaging rays.
07

Current State of Earth's Atmosphere

The present atmosphere consists mainly of nitrogen (78%) and oxygen (21%), with small amounts of other gases including argon, carbon dioxide, and the vital ozone. This is the product of more than 4 billion years of evolution and the life-sustaining processes occurring continuously on our planet.

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