Most modern organisms, including us, could not live on Earth if it didn’t have the atmosphere it has. On the other hand, the atmosphere would not be the same without the influence of some early organisms. The modern atmosphere is not the same as when the Earth formed, approximately 4.6 billion years ago. ¿How did the evolution of the atmosphere occur? ¿What do volcanoes, algae, and plants have to do with it? We’ll learn about the stages of atmosphere evolution, its timeline, and some interesting facts about it.
Evolution of the Atmosphere: Definition
The atmosphere is a layer of gases that surrounds a planet.
Earth’s atmosphere is composed of several layers that are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The modern-day atmosphere contains a mix of gases (nitrogen, oxygen, argon, carbon dioxide, and other gases).
Check The Earth’s Atmosphere article to know all about it!
Earth's atmosphere has changed over time. When the planet first formed, it was inhospitable. Earth's surface averaged a scorching 2000ºC, while volcanoes constantly spewed lava and toxic gases.
It was in no state to support bacteria, let alone plants and animals.
The Earth has undergone many changes in the past four billion years. It's experienced ice ages, hot periods, and millions of different life forms. It's impossible to know what the Earth was like billions of years ago, but scientists can study rocks, fossils and ice cores to get a good idea of past climates and atmospheric conditions. Scientists have combined their evidence to produce a theory - the evolution of the atmosphere.
Stages of Evolution of the Atmosphere
The evolution of the atmosphere that we inhabit today can be split into three main stages: the early atmosphere, ocean formation, and the biological era.
The Early Atmosphere
When the Earth first formed, it had no atmosphere. The planet was a sweltering ball of molten rock under constant strike by asteroids and rocks. When the bombardment began to slow down, a thin atmosphere was created from hydrogen and helium, the most abundant elements in the universe.
Volcanoes formed the first true atmosphere. When they erupted, they spewed carbon dioxide, nitrogen, hydrogen and water vapour. Gradually, the atmosphere filled up with these gases.
Hydrogen and helium (which are much lighter than volcanic gases) escaped into space.
Fig. 1: In Earth's early days, there were volcanoes everywhere, unsplash.com.
Cooling and Ocean Formation
After a few million years of volcanoes and sweltering heat, the planet gradually began to cool down. The water vapour condensed into a liquid, and rain fell for centuries, filling up the rock basins to form oceans.
Carbon dioxide dissolved into the water, creating carbonate compounds. These compounds were then precipitated to form sedimentary rocks and fossil fuels.
When a compound is precipitated, it means it is deposited in a solid form from a solution.
The Biological Era
The oldest pieces of evidence for life on Earth are stromatolites, which appeared 300 million years after the formation of the oceans.
Stromatolites are layered rocks that form when cyanobacteria (microscopic photosynthesising organisms) bind films of sediment together.
Photosynthesis caused a significant shift in the Earth's atmosphere.
Photosynthesis is the process of converting carbon dioxide and water into glucose and oxygen using the energy from sunlight.
Oxygen (O2) is a byproduct of photosynthesis. Initially, rocks took up most of the oxygen produced, so it didn't build up in the atmosphere. It wasn't until algae evolved that atmospheric oxygen levels began to increase almost a billion years later. As photosynthesis increased, carbon dioxide (CO2) was used up and slowly removed from the atmosphere.
Atmospheric oxygen also forms the ozone (O3) layer - which helps protect us from the devastating effects of high-energy UV (ultraviolet) rays from the sun.
Did you know that about 70% of the oxygen we breathe comes from algae in the ocean?
Simple aquatic animals began to evolve 800 million years ago. As plants diversified, oxygen levels increased, enabling more complex animals to develop.
The Modern Day Atmosphere
The water vapour cooled down to form oceans. The carbon dioxide got used up and replaced by oxygen. But what about the nitrogen from volcanic eruptions?
Nitrogen is an inert gas, so it didn't react with anything. Its unreactivity allowed it to slowly build up until it became the dominant gas in today's atmosphere.
Gas | Percentage (%) |
Nitrogen | 78 |
Oxygen | 21 |
Argon | 0.9 |
Carbon Dioxide | 0.04 |
Other Gases | 0.06 |
Table 1: The gases present in the atmosphere and their current percentages.
Evolution of the Atmosphere: Timeline
From the formation of the Earth to the invention of the sewing machine, Earth's atmosphere has changed and affected life on the planet.
- 4.6 billion years ago: Earth was formed. The temperature was too hot to sustain life, and volcanic eruptions were constant.
- 3.8 billion years ago: Earth's temperatures cooled to below 100ºC. Water vapour in the atmosphere condensed, creating oceans. Some carbon dioxide was locked into rocks.
- 3.5 billion years ago: Life first evolved in the oceans, forming stromatolites.
No one knows how life came about, but there are two main theories.
- Primordial Soup Theory: Solutions of organic molecules were present in the oceans. Energy for protein synthesis comes from a lightning strike or UV radiation.
- Deep-sea Hydrothermal Vents: alkaline vents have a high pH and warm water (maximum 90ºC). Life evolved in water ejected from these vents.
- 2.7 billion years ago: Algae evolved. Atmospheric carbon dioxide decreased, replaced by oxygen.
- 1.8 billion years ago: The first eukaryotes evolved. These organisms are more complex than bacteria.
- 800 million years ago: The first simple animals evolved.
- 540 million years ago: Increased oxygen levels enabled rapid animal evolution. This period is known as the Cambrian Explosion.
- 200,000 years ago: Homo sapiens (modern humans) evolved on the continent of Africa.
- 200 years ago: Industrialisation began affecting the Earth's atmospheric composition and climate.
The Gas Percentages of Earth's Early Atmosphere
It's impossible to know the atmospheric composition billions of years ago, but experts have made educated guesses. Constant volcanic eruptions suggested that Earth's atmosphere was mainly carbon dioxide, with some water vapour and small amounts of nitrogen. Methane and ammonia were present in trace amounts.
Oxygen was most likely absent entirely.
Earth's early atmosphere has often been compared to modern-day Venus, whose atmosphere is 96.5% carbon dioxide. As a result, Venus's atmosphere is over 90 times denser than Earth's and produces a powerful greenhouse effect, raising surface temperatures to over 470ºC.
Evolution of the Atmosphere: Facts
Find below a list of facts about the evolution of the atmosphere!
Redbeds are sedimentary rocks primarily red in colour due to the presence of iron oxide.
Despite rising temperatures, we currently live in an ice age! This ice age began approximately 3 million years ago and peaked around 20,000 years ago. We are experiencing an interglacial period of warmer temperatures within the ice age.
An ice age is a long period when global temperatures are relatively cold, and continental ice sheets and glaciers cover large areas of the surface.
Fourteen thousand years ago, temperatures began to rise as the new interglacial period began. Many large, cold-adapted mammals (including the woolly mammoth, the woolly rhinoceros and the wild horse) went extinct.
Fig. 2: Several thousand years ago, most of the UK was covered by ice, unsplash.com.
The Earth's atmosphere is divided into five layers - the troposphere, the stratosphere, the mesosphere, the thermosphere and the exosphere. Temperatures in the different layers can vary drastically.
The mesosphere can fall to -90ºC whilst the thermosphere can reach 2000ºC.
To recap, Earth's early atmosphere was dominated by carbon dioxide and water vapour from volcanoes. As temperatures cooled, the water vapour condensed. The newly formed oceans were the birthplace of life. Photosynthesis replaced carbon dioxide with oxygen, enabling a wide variety of plants and animals to evolve.
Evolution of the Atmosphere - Key takeaways
The first atmosphere was formed from gases emitted by volcanoes - mainly carbon dioxide, some water vapour and trace amounts of nitrogen, methane and ammonia.
3.8 billion years ago, Earth's temperature fell and the atmospheric water vapour condensed to form the oceans. The oceans absorbed some carbon dioxide.
2.7 billion years ago, algae evolved, and photosynthesis began. The carbon dioxide in the atmosphere was used up, and oxygen was produced.
High levels of oxygen enabled the evolution of complex life.
Nitrogen's unreactivity allowed it to build up until it became the dominant gas in today's atmosphere.
Today's atmospheric composition: 78% nitrogen, 21% oxygen, 0.9% argon, 0.04% carbon dioxide.
References
- Ian Sample, Human-induced climate change began earlier than previously thought, The Guardian, 2016.
- John Grotzinger, Understanding Earth (International Edition), 2019.
- Jon Shonk, Introducing Meteorology: A Guide to Weather, 2013.
- Michon Scott, What’s the hottest Earth has ever been?, EarthSky, 2016.
- National Geographic Society, Atmosphere, 2022.
- National Geographic Society, Formation of Earth, 2022.
- National Museum of Natural History, History of Life on Earth, 2022.
- National Oceanic and Atmospheric Administration, Why do we have an ocean?, 2021.
- National Science Foundation, Large Ice-Age Mammal Extinctions: Humans and Climate the Culprits, 2011.
- Neil Campbell, Biology: A Global Approach Eleventh Edition, 2018.
- Regents of the University of Michigan, Evolution Of The Atmosphere: Composition, Structure And Energy, 2022.
- Revise Chemistry, AQA GCSE Chemistry of the Atmosphere, 2020.
- Sandy Eldredge, Glad You Asked: Ice Ages - What Are They and What Causes Them?, Utah Geological Survey, 2019.
- Smithsonian Environmental Research Centre, Atmosphere, 2002.
- Twinkl, AQA GCSE Chemistry (Combined Science) Unit 9: Chemistry of the Atmosphere, 2022.
- University of the Basque Country, Venus compared with the Earth, 2022.
- Fig. 1: Image of a volcano (https://unsplash.com/photos/g6tqHx0ME1o) by Jonatan Pie, free to use under the Unsplash License (https://unsplash.com/license).
- Fig. 2: Image of ice cap (https://unsplash.com/photos/skam8BzESHo) by Adventureontheside.com, free to use under the Unsplash License (https://unsplash.com/license).
Explanations 
Exams 
Magazine 
