Welcome to the fourth and current eon of Earth’s history, the Phanerozoic Eon. In this blog we will explore the last 538 million years of Earth 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 Phanerozoic Eon
The Phanerozoic Eon was named after the Greek ‘phaneros’, and ‘zoē’ meaning ‘visible’ and ‘life’. This name was given to the eon by geologists in the 19th century.
The Phanerozoic Eon lasts from 538 million years ago to today. The beginning point of 538 million years does vary from source to source. Some say 540 or 541, but the gist is, 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.
Key Features of the Eon
This eon is all about the explosion and diversity of life, particularly how life evolved into new branches were wiped out, and then evolved into other new branches. The eon began with the Cambrian Explosion and the main categories of vertebrates evolved in rapid succession. They went from fish, to amphibians, to reptiles and to mammals. Plant life came onto land and eventually evolved into flowering plants. There were five big mass extinctions. And of course, us.
The Cambrian Explosion was a monumental event, so much so that time before this, the previous three eons we have studied, are sometimes referred to ‘pre-Cambrian’. Occasionally in some works, the ‘pre-Cambrian’ time is simply lumped into one category as if not much happens before the Cambrian period and everything happens after the Cambrian. Not true. We have seen many amazing things happen in the previous three eons. While life is important on Earth, it isn’t the only thing that has happened.
The beginning of this eon saw the evolution of the skeleton, which made organisms fossilize a whole lot easier compared to earlier soft-bodied organisms. It is thought that external shells were the first types of bones and exoskeletons to evolve because they protected the soft-bodied organisms from what was rapidly growing to be the dominant method of eating, predator and prey. There are only so many plants and other organic matter that can sustain certain life forms in the deep oceans. Organisms began moving and evolved to eat each other as a source of energy.
Thus the predator and prey game between animals began, with each species evolving better methods of hiding and hunting which in turn increased the need for the skeleton both exo (external) and endo (internal) to be more versatile. This increased the need for sight and sensory organs and a brain to process external information that was crucial for survival. It increased the need for behaviour patterns to develop further and understand the environment, in order to detect food and avoid getting hunted. As species diversified and filled new niches, competition increased.
This eon sees a huge jump, albeit based on the billions of years of foundational evolution, in complex organisms. It went from jawless fish, to fish with jaws, who then came onto the land and adjusted to life on land. Then amphibians who were not entirely adjusted to life on land, however they did evolve into another group called reptiles who were adjusted to living entirely on land. Reptiles led to dinosaurs and birds, and another group emerged called the mammals.
At any one time, it did feel like a group of organisms were dominant. The charming names like the Age of Fish and the Age of Reptiles, indicates this evolutionary journey and what the dominant organisms were. The Age of Fish began around 419 million years ago. The Age of the Forests began around 370 million years ago which is responsible for our modern day coal deposits. The Age of Amphibians began around 320 million years ago. The Age of Reptiles began 252 million years ago. The Age of Mammals began 66 million years ago.
Plant life also evolved during this eon. It was around 470 million years ago when the first plant species went onto land. It was during the Carboniferous period, 358 – 298 million years ago, when forests covered the landmasses with huge trees. At this time, there weren’t large enough predators on land yet to balance it out and eat them so they overtook the land. This incidentally increased oxygen in the atmosphere leading to enlarged insects and caused massive erosion, as the huge trees would have sucked up a lot of nutrients and water from the surrounding oceans and water sources. The first flowering plants evolved around 135 million years ago, which accounts for everything we eat today from wheat to fruit to spices in our tea.
The five mass extinctions began with the Ordovician event 444 million years ago and ends with the asteroid that wiped out the dinosaurs 66 million years ago. Each event had its own root cause and took different lengths of time to recover.
Of course we can’t discuss the current eon without a mention of our own species. We stemmed from primates who evolved once the dinosaurs were wiped out. The mammals essentially had room to diversify and took over niches that were once inhabited by the dinosaurs. Around 7 million years ago, the genetic line between chimpanzees and our ancestors split. Around 2.5 million years ago, other species in our genus Homo, evolved. Around 300,000 years ago is when our species, sapiens, evolved.
Subdivisions
The eon is divided into three eras of time, and further into periods and epochs of time as so much happened and continues to happen.
Let’s explore some of the features above and put them into perspective of when they happened, and thus how some of the time periods are split up.
Paleozoic Era – 538 – 251 million years ago (287 million years long)
This era of time is further divided into six periods of time.
The Cambrian was the first, where life rapidly diversified in the oceans and we saw one of the most successful species of all time, the trilobites.
The Ordovician period was when we got massive diversification in marine life and plants went onto land for the first time.
The Silurian period was when life on land diversified and early arthropods came onto land like millipede type organisms. We saw jawed fish as well.
The Devonian period was dubbed Age of Fish, we got the first amphibians, land (terrestrial) plants flourished and insects adapted to land.
The Carboniferous period saw vast forests on land and the first reptiles evolved. There were also giant insects around at this time due to high oxygen levels from those massive forests.
The Permian period saw the dominance of reptiles, but the decline of marine life. This period and eon ends with the greatest of extinction events, wiping out up to 96% of marine life and 70% of terrestrial life.
Mesozoic Era – 251 – 66 million years ago (185 million years long)
This era of time is further divided into three periods of time. It was the time of the dinosaurs.
The Triassic period saw recovery from the extinction event from the previous era, end of the Permian period above. We have the first dinosaurs, early mammals and marine life bounced back.
The Jurassic period saw dinosaur dominance, the first birds, marine life expanded, the first flowers and mammal evolution.
The Cretaceous period saw the peak of the dinosaurs with the famous ones like T-rex. Birds were advancing in flight capabilities, there was an explosion of flowering plants and we saw huge marine animals. The end of this period and era saw the last of the big five extinction events, an asteroid hit Earth and wiped out 75% of life, including all non-avian dinosaurs meaning all dinosaurs except the birds.
Cenozoic Era – 66 million years ago to today.
This era of time is divided into three periods.
The Paleogene period saw mammals diversify after the extinction event above, apes and monkeys evolved, grasslands expanded, flowering plants expanded, marine life and birds flourished.
The Neogene period saw expansion of mammals like saber-tooth cats and mammoths, we saw early hominines evolved bipedalism (walking on two legs) and animals adapted to open landscapes.
The Quaternary period (current period of time) saw ice ages and the evolution of the Homo species. Also extinctions of mega-fauna like mammoths. We also saw the evolution of civilisation and all that is modern including significant climate change.
Summary of the Eon
As this is the current eon, we can only summarise so much. We have seen how rapidly life diversified in the last 538 million years, after the culmination of the previous 3 billion years of the evolution.
This is the eon we can relate to the most. We can learn from other animals, how they lived, what brought on their evolutionary behaviour, how that trickled down the family tree to our ancestors and to us. We can learn from the climactic events that occurred, the mass extinctions and how long they took to recover. We can see clearly the chain of causation that led to our current ecosystems, which only really developed in the last few hundred million years. Compared to the life span of the earth and the 3 billion years of life that came before it, a few hundred million years isn’t a lot of time.
Lesson to Take Away
There are a few lessons we can take away from this eon. Not just for personal growth, but practical lessons for the future, to protect what we have destroyed in nature.
Build Solid Foundations
We can see in this eon how diversity of life exploded, even near the beginning of the eon. Within the first couple hundreds of millions of years, we saw massive diversity, and it just kept going. This however sprung up from 3 billion years of evolutionary foundations. The explosion of ‘successes’ cannot occur properly without the solid foundation.
We can take this analogy and apply it to modernity and the various things we attempt to do. Whether it’s health goals, romantic goals, or work and money goals. We cannot hope to flourish in these areas unless we do work on the foundations, work upwards. For health, its understanding your own body and personal needs; then understanding your own habits and what you wish to work on or improve; then having an action plan from a professional to improve your health. With work it’s a similar process, understand yourself and your habits, align them with what you want and become aware of what works and what you need to adjust in order to meet your goal.
It’s about understanding and facing the reality of your situation and understand that you cannot flourish in a positive manner without working on those foundations first.
The Greater The High, The Further The Fall
This eon demonstrates the principle of what goes up, must come down. There were moments of rapid speciation (increase of diversity and number of species) however the extinction events were as great in their destructiveness. It’s almost as if the risk increases. The greater the height, the more intertwined and complex, the more there is to lose.
Put simply, the more you have, the more you have to lose. It’s not to say, don’t have things. But it’s a message to pay attention.
We have amazing bodies that work automatically and so efficiently. We have very little control over our bodily functions. The most we can do is move around by choice, decide what to externally consume but when it comes to the internal workings, we have literally no control over them. And yet, the smallest incident, injury or bad consumption habit can destroy this beautiful body we all possess. We will and do pay for our bad choices, with pain and suffering.
This lesson is about increasing awareness, that by default even if we have no material possessions, we have this amazing body. That in itself is something to be aware of, to look after and to understand that it can down and suffer very quickly if we’re not careful.
Extend this awareness out to the external life of who you have in your life and then the material things. Increase your awareness of yourself and your choices.
A Delicate Intertwined Balance
This eon teaches us the complexity of life and how things are inherently interconnected. We do not live in isolation. While it is somewhat comforting and delusional to think and behave as if we are in isolation, as if my individual actions don’t affect anyone but myself, or that this part of my life doesn’t affect the other parts, that’s not reality.
As we can see with geological and biological events in this eon, the moving of continents, the eruption of a volcano causes ripple effects across the whole system. Why? Because everything it connected. That’s how our world, our civilisation, our bodies have evolved. We wouldn’t be here if it wasn’t for this holistic way of being, we need to understand it and embrace it more.
We can see this in our civilisations and global systems. The act of one company in one country can have ripple effects on a society across the world. Become more aware of how the world is connected, not just in nature, but within modernity.
Further Exploration
We have explored the fourth and current 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 tree of life and taxonomy, into mass extinctions, into hominine evolution or into the history of dinosaurs.
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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