How has the composition of the earth's atmosphere changed over time?

Question

Isaac Abel · Accepted Answer

Our planet's atmosphere has changed quite a bit over time. See the explanation below.

The planet is generally thought of as having three distinct atmospheres over the course of its lifetime.

When earth was first formed, its atmosphere was likely composed of hydrogen, helium, and other gases that contained hydrogen. Yet this atmosphere didn't last for very long because the solar wind from the sun blew it away. Solar wind is stream of charged particles such as electrons, protons, and alpha particles. We now have a magnetic field surrounding earth that shields us from solar wind.

The second atmosphere formed a little after 4.5 million years ago (mya) and was produced due to volcanic outgassing. Outgassing is the release of gas that was trapped in some other material. In this case, volcanic outgassing released hot gases trapped deep within the interior of the planet. Water vapor, carbon dioxide, methane, ammonia, and other gases similar to the ones produced by volcanoes today were expelled.

Over a vast amount of time, millions of years, the earth gradually cooled. When the temperature dropped enough, water vapor condensed and went from a gas to liquid form. This created clouds. From these clouds, the oceans formed and the oceans absorbed a lot of the carbon dioxide in the atmosphere. A small amount of oxygen was produced by the photolysis of carbon dioxide and water vapor by ultraviolet radiation.

Lastly, we have the third atmosphere. Around 2.5 mya, the amount of oxygen available in the atmosphere started to rise due to the evolution of photosynthetic organisms that produced oxygen. These organisms were oceanic cyanobacteria. Over time, aerobic organisms evolved and consumed some of the oxygen produced. Read more about how oxygen became a major part of our atmosphere here.

This is the composition of the atmosphere we have today:

Violet Adams · Answer

The present day atmosphere has arisen from long drawn out processes wich have been taking place on Earth

Earlier, there was an abundance of methane and nitrogen, ammonia and almost nil percentage of oxygen.

But these conditions created life, which expanded and took in carbon compounds to give oxygen molecules or its compounds. About 3 billion years ago, these life forms which we often call plants, ruled the planet. By this time there was an abundance of oxygen, some CO2 or carbon compounds, and huge amounts of nitrogen.

Mila Bautista · Answer

undefined The composition of the Earth's atmosphere has changed over time due to various factors such as volcanic activity, biological processes, and human activities. Initially, the atmosphere was primarily composed of hydrogen and helium. However, through processes like volcanic outgassing, water vapor, carbon dioxide, and nitrogen were released, gradually altering the composition. Early photosynthetic organisms contributed oxygen to the atmosphere, leading to the development of an oxygen-rich atmosphere around 2.4 billion years ago during the Great Oxygenation Event. Over the past few centuries, human activities, particularly industrialization, have significantly increased the concentration of greenhouse gases such as carbon dioxide and methane, leading to concerns about global warming and climate change.

Aaron Anderson · Answer

undefined The composition of the Earth's atmosphere has changed significantly over geological time scales. Here are some key changes:

1. **Early Atmosphere (3 to 4 billion years ago)**:
   - **Primordial Atmosphere**: Composed mainly of hydrogen (H2) and helium (He), similar to the composition of the solar nebula from which the Earth formed.
   - **Outgassing**: Volcanic activity released gases like water vapor (H2O), carbon dioxide (CO2), nitrogen (N2), methane (CH4), ammonia (NH3), and sulfur compounds.

2. **Formation of Oceans**:
   - Water vapor condensed and formed the Earth's oceans. This led to a reduction in the amount of water vapor in the atmosphere.

3. **Development of Life**:
   - **Photosynthesis**: Cyanobacteria and early algae started producing oxygen (O2) through photosynthesis.
   - **Increase in Oxygen**: Over several hundred million years, oxygen levels began to rise, leading to the "Great Oxygenation Event" around 2.4 to 2.3 billion years ago.
  
4. **Modern Atmosphere (last few million years)**:
   - **Nitrogen Dominance**: Currently, nitrogen (N2) makes up about 78% of the atmosphere.
   - **Oxygen**: Oxygen (O2) accounts for approximately 21%.
   - **Trace Gases**: Other gases like argon (Ar), carbon dioxide (CO2), neon (Ne), helium (He), methane (CH4), and ozone (O3) make up the remaining 1%.

5. **Human Influence (last few centuries)**:
   - **Increase in CO2**: Industrial activities, deforestation, and the burning of fossil fuels have led to a significant increase in carbon dioxide levels in the atmosphere.
   - **Other Greenhouse Gases**: Methane (CH4), nitrous oxide (N2O), and fluorinated gases have also increased due to human activities.
   - **Ozone Depletion**: The release of chlorofluorocarbons (CFCs) led to ozone layer depletion, although international efforts have reduced the production of these compounds.

In summary, the Earth's atmosphere has evolved from a primordial mix of gases to the nitrogen-rich composition we have today, with significant fluctuations and changes driven by geological processes and the emergence of life. Human activities in recent centuries have further altered the atmospheric composition, leading to concerns about climate change and environmental sustainability.