Earth’s Early Atmosphere

As I discussed in my previous post, the Earth’s climate is not only changing today, but it has changed for billions of years and will probably continue to do so long after us humans are gone. Generally, Earth’s climate history shows that dramatic swings in climate occur over the course of tens of thousands, to millions of years. However, the point of this blog is to explain that our brains can’t truly fathom these tremendous amounts of time and if we observe the changes that Earth has seen in the past over these geologic periods, we can see the changes in climate observed today are occurring at an increasingly alarming rate.  


For my remaining posts beyond this point, we will be observing several instances in which the Earth’s climate has changed in the past. Including all instances where the climate has changed since the beginning of time would be nearly impossible. As a result, we will start at the very beginning and make our way to the present, while investigating some major climate turning points occurring between them. Additionally, we will be briefly discussing the mechanisms (natural and human-caused), that could be capable of driving the changes that will be investigated. Finally, toward the end of the blog posts, we will observe the climate change that is being monitored today and prove that humans are dramatically speeding up Earth’s natural processes and negatively impacting not only the Earth and its climate, but life as we know it.  

-Origins of the Earth, Moon and Ocean 

At the time when the solar system was first formed, billions of years after the big bang, Earth’s first surface and atmosphere (composed of an outer layer of gases), was formed as well. This is thought by scientists to have taken place around 4.6 billion years ago (Garrison and Ellis 2016, 12). Shortly after the Earth’s surface formation, a planetary body larger than Mars smashed into the relatively newborn Earth. As a result, most of the rocky mantle was ejected into space and condensed to form the moon.  

An image of what the collision between the moon-to-be and the Earth could have looked like. (NASA)

After this collision, gases that were trapped inside the forming planet were burped to the surface to form Earth’s second atmosphere, made mostly of carbon dioxide, methane, and water vapor. This venting of gases from the hot mantle and volcanic surface is known as outgassing and this process releases greenhouse gases like water vapor and carbon dioxide into the atmosphere. At the time, Earth’s atmosphere was so hot that water could not collect on the surface. As a result, the hot vapors rose to the cool upper atmosphere and condensed to form thick clouds. 

After millions of years, the clouds cooled enough to form droplets. These hot rains fell to Earth but evaporated again before they could reach the ground. As the surface became cooler, rain reached the ground and water began to fill lower-lying areas, dissolving salty minerals from the underlying rocks. Some of the water evaporated and fell back to the Earth again, but the dissolved salts were left behind. For approximately 20 million years, the rains continued, and so did the outgassing from volcanic activities (Garrison and Ellis 2016, 14). The world’s ocean was born and growing.  

Some scientists also believe that much of Earth’s water came from comet and asteroid collisions. These frozen rocks carry much of the makings/elements of the solar system.

-The Origins of Life 

Approximately 3.5 billion years ago, the atmosphere gradually shifted to a composition similar to today’s, consisting of mostly oxygen and nitrogen, rather than carbon dioxide. This process was made possible by ocean acidification, which is when the ocean takes carbon dioxide out of the atmosphere and forms carbonic acid. Additionally, around this time, the first life-forms on Earth were flourishing in the oceans.  

These microbes, known as cyanobacteria, were microscopic organisms that were able to survive by producing oxygen from carbon dioxide, water, and sunlight, otherwise known as photosynthesis. Over time, this population of microscopic organisms grew large enough to allow oxygen to accumulate in the atmosphere, transforming the Earth and its inhabitants for the rest of time (The Great Oxidation Event).

Cyanobacteria: Earth’s first life (CSIRO)
Stromatolite rocks in Australia contain preserved communities of these cyanobacteria.
Earth: 2.5 Billion Years Ago 

As a result of the build-up of oxygen in the atmosphere, the greenhouse gases, methane and carbon dioxide, were displaced by the accumulating oxygen. Oxygen eventually overwhelmed the presence of carbon dioxide and methane in the atmosphere, meaning that there were little greenhouse gases to keep the Earth warm ( This would be something like throwing off your blankets in the middle of a cold night. Over time, Earth was sent into its first ever ice age. Life on Earth that did not freeze to death, died of oxygen poisoning. Life that was able to beat the cold and adapt to the increased oxygen levels survived, allowing life to evolve into more complex microscopic organisms. Some scientists consider this ice age, associated with the displacement of greenhouse gases, the first ever mass extinction of life on Earth. 

The Huronian Ice Ages: 2.4 – 2.1 Billion Years Ago 

As previously mentioned, concentrations of greenhouse gases in the atmosphere dropped. The greenhouse effect collapsed, and global temperatures dropped, sending the planet into a series of ice ages. When the first sheets of ice were formed, a greater area of land was covered by ice, which is white. This means that more solar radiation was reflected into space, thus enhancing the global cooling effect and causing the ice to spread even further. The accompanying glacial and interglacial periods for this ice age likely lasted 300 million years with evidence suggesting the climate reached “snowball Earth” conditions for the first time. Scientists believe this would be the longest ice-age in Earth’s history, likely due to a dimmer sun, as well as a lack of volcanic activity at the time, which further reduced carbon dioxide and methane concentrations in the atmosphere. These ice ages were followed by the beginning of the first greenhouse period, which lasted from an astounding 2.1 billion to 720 million years ago. We’ll talk more about greenhouse periods later.  

An artist’s depiction of what “snowball Earth” may have looked like.
(Chris Butler)


There are a few things we can take from this investigation. First, to understand how climate change is impacting us now, it is important to understand how it has occurred and impacted the world in the past. The origins of the Earth, the moon, and the oceans set the stage for a new atmosphere that was destined for change. Additionally, these events lead to the initiation of life on Earth, and even billions of years ago, life significantly impacted the amount of greenhouse gas in the atmosphere, and thus the climate of Earth. We saw how microscopic bacteria can influence extreme changes in climate. 

 Just wait until humans come into the picture… 

Next post: coming soon…

-Andrew Bower

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