The Timeline of The Proterozoic Eon

Proterozoic Eon. Fine Art by Perveen Kaur

Welcome to the third and longest eon of Earth’s history, the Proterozoic Eon. In this blog we will explore what happened in this eon by looking at the timeline of this eon, some key features and the subdivisions. 

We have other blogs that explore in detail the other eons of Earth’s history.

Overview of the Proterozoic Eon

The Proterozoic Eon was named after the Greek ‘proteros’, and ‘zoē’ meaning ‘earlier’ and ‘life’. This name was given by geologists in the late 19th and early 20th century. It is so named because it’s the eon where early life flourished laying the foundations for complex life. 

The Proterozoic Eon lasted from 2.5 billion years ago to around 538 million years ago, a whopping 2 billion years long. The end point of 538 million years does vary from source to source. Some say 540 or 541, but the gist is that it’s around this time. We will use 538 million years. 

For this blog, we will be referring to the image below as our timeline. 

Timeline of the Proterozoic Eon by Perveen Kaur

Key Features of the Eon

This eon saw a rise in oxygen levels due to the events of the previous Archean Eon. The early life that evolved in the previous eon, transitioned into multi-cellular life and tectonic activity heightened leading to supercontinents and global glaciations (ice ages). 

A major feature of this eon was the rise in oxygen levels. We saw in the previous eon, the Archean, that cyanobacteria had evolved to photosynthesise. This means that the by-product of oxygen, flooded the oceans and the atmosphere. This led to the Great Oxygenation Event (GOE). This was a mass extinction event. The free oxygen that flooded the atmosphere killed the early organisms that evolved in an anoxic atmosphere (atmosphere with no oxygen). Oxygen was essentially poisonous to these early organisms, just like breathing in too much methane and carbon dioxide would be fatal to us (not poisonous per say, but fatal. 

Another feature of this eon is the breaking and making of continents leading to the supercontinents. A confirmed one is Rodinia which formed around 1.3 billion years ago. As the continents moved and shifted, it caused huge effects in the oceans and for life in those oceans. At this time, life was only in the oceans and was still at a small physical size however as we will see in the next eon, major shifting of continents had devastating effects on complex life. 

The glaciations (ice ages) of this eon lasted millions of years. The causes of them were varied. There was a time around 720 million years ago that the Earth was plunged into an ice age event that lasted for 70 million years. During this time the Earth experienced several Snowball Earth events, where the entire earth was apparently covered in ice from pole to pole and right up to the equator. Life still survived in the oceans though. 

The early life forms were prokaryotes, single celled organisms. As time moved forward into this eon, these evolved into eukaryotes which were far more complex in their structure and function. These eukaryotes would lay the groundwork for the complex organisms coming in the next eon, animals. 

Towards the end of this eon we see multi-cellular life take the next step forward in its evolution. We observe Ediacaran fauna, which are the earliest signs of complex life. The eon ends with the extinction of the Ediacaran fauna, however after this comes the big explosion of complex life. Death begets life. Extinction begets speciation. In order for something to evolve and thrive, in theory something else has to die. There is a cost so to speak, a price to pay, an exchange of energy. 

The two extinctions mentioned above, the GOE and the extinction of Edicaran fauna, don’t officially come under the Big Five mass extinctions, however they are still important in the history of life. 

Subdivisions

This eon sees three subdivisions of eras which are hundreds of millions of years long. These are then further divided into periods which tend to be tens of millions of years long as we can see in the timeline above with the large pink dots. 

Paleoproterozoic Era – 2.5 to 1.6 billion years ago (900 million years long)

The eon began with the Great Oxygenation Event (GOE) which flooded the atmosphere with free oxygen. The first eukaryotes evolved from prokaryotes and we see the stabilizing of the continental crust. 

This is era is subdivided further into four periods. 

Mesoproterozoic Era – 1.6 to 1 billion years ago (600 million years long)

This era of time saw the movement of landmasses creating supercontinents such as Rodinia. The eukaryotes continued their evolution eventually leading to dominance of the seas. We also saw the emergence of the first multi-cellular organisms like algae. 

This era is further subdivided into three periods of time. 

Neoproterozoic Era – 1 billion to 538 million years ago (462 million years long)

This is the era of major global ice ages leading to the phenomenon of Snowball Earth and ice ages that lasted millions of years. This era of time ended with the evolution of the Ediacarn biota which included soft-bodied organisms. However there was an extinction event at the end of this era of the Ediacaran biota, leading the way for complex animals to take dominance. 

This era is further divided into three periods. 

Summary of the Eon

This eon represented the next big shift of Earth and of life. The stability we saw in the previous eon, the Archean, has taken hold and created some truly magnificent events. The emergence of eukaryotes and multi-cellular life was the next stepping stone on the way to complex organisms, known to us as animals. We saw major geological events such as stabilised crust, continent movement and ice ages. Life survived these major events and thrived in the oxygenated atmosphere. 

These changes laid the foundation for the following and current eon of geological time, the Phanerozoic, where we see complex life take over, and organisms come onto land and into the skies. We see massive diversity in animals and major extinction events. 

Lessons to Take Away

This eon provides some key things we can take away and apply to living and coping with modernity. 

Poison To You, Isn’t Poison To Me

We can see in this eon the Great Oxygenation Event which is in turn, a mass extinction event. It highlights the difference between organisms and what different organisms are evolved for. 

As we move forward in our own lives, we have and will encounter people who are different, with different points of views and different preferences. The fact is that every person on the planet is a different person, with a slightly different cocktail of genes, emotions, experiences, reactions and traits. While we all possess the basic human traits, our personalities and experiences shape us to be very different people. What is right for you, isn’t going to be right for someone else. 

This is a crucial lesson to learn. We are not always right. And other people are not always wrong. We have tremendous ego as a species, it’s one of the factors that allowed our species to grow to such heights. However our ego can stop us from seeing reality, from getting along with other people and accepting new points of view. 

Extinction Begets Speciation

This basically means that without extinction, we don’t get new species. There is finite amount of energy and space on Earth. Just like there is a finite amount of time that we experience in our lives. And a finite amount of physical, emotional and mental energy.

Just how species die out to make room for new species, old habits need to die out to make room for new ones. As our environment changes, and it does always change, we have to adapt along with it. Many of us continue to hold onto old habits in new situations because it’s all we know, and then get disappointed in the results. 

We can learn from this, to understand and bring awareness to our habits, especially if one is unhappy and suffering. We can shift a lot in our lives by simply turning inwards and assessing our own habits, to understand what is working for us and the environment we are in, and what simply isn’t working anymore. What part of you isn’t serving you in your current environment? It might be time to let it go and develop new habits that are better suited to who you are today and the environment that you are in. Adaptation is key to sustained and healthy longevity. 

Further Exploration

We have explored the third and longest eon of Earth’s history, the timeline and subdivisions of time, the features of this eon that made it special and some lessons we can take away from it. 

To further your education on this topic outside of Evolution of Stuff, you can explore deeper into the ice ages of this eon, the development of life, what is Ediacaran biota and some supercontinents of old. 

At the end of this blog are the links to some of our other blogs, so you can continue your exploration and education. 

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