What Was Earth Like Before Dinosaurs?

When we think back millions of years ago, long before recorded history, we usually think about dinosaurs, but life on Earth actually existed for billions of years before the first dinosaur came into the scene! Though, it was very different to what you might imagine. Let's go on a wild journey from Earth’s very first days all the way through to the dawn of the dinosaurs!

The Beginning

As with most things, it’s a good idea to start at the start. Around 4.6 billion years ago, dust and gas left over from the Sun’s formation bunched together to create colossal space rocks hundreds of miles across. This is a massive simplification, but these collided with one another over and over and eventually fused to create the Earth, though, certainly not an Earth recognizable to you or me.

This early Earth was a hellish, molten world of superheated lava, radioactivity, and regular asteroid impacts. And that was it! For a long, long time. It wouldn’t be until almost a billion years later, around 3.7 billion years ago, that things would get interesting.

By this time, our planet had cooled significantly and was near modern temperatures. That doesn’t mean it was hospitable though. Largely composed of water and with the atmosphere mostly devoid of oxygen, it was an empty world of tumultuous seas and rocky crags. The only noise you’d have heard was the ceaseless crash of the tide colliding with the shore. That, and the occasional volcanic eruption.

Yet, deep within the waters of this spooky place, something amazing, and utterly perplexing, happened. Life was born. We’re not exactly sure how, but a miraculous blend of the right processes and ingredients in the Earth’s oceans led to extremely simple, single celled organisms emerging. And some of these organisms produced oxygen.

For billions of years our single celled friends were free to laze around absorbing nutrients and expelling their own byproducts. But ever so slowly, they began to change and grow more complex. This would finally come to a head at the start of the Cambrian period, some 538 million years ago.

Before the Cambrian, the Earth’s landmass had formed one supercontinent called Rodinia. As the Cambrian began however, this would split into several smaller landmasses, the biggest of which was Gondwana, in the south-east. But that’s not the exciting part.

The Cambrian Explosion

Allow me to introduce you to the Cambrian explosion, the most incredible biodiversification event in the history of our blue planet. But it wasn't a big fiery bang, this explosion was more metaphorical to describe the sheer number of new creatures that burst onto the scene.

Single cells were so last millennia. Now complex life was in vogue! Most of the basic body forms we see today first appeared at this time, and relatives of crustaceans, mollusks, starfishes, and worms developed beneath the waves.

Don’t get me wrong, this “explosion” still took place over tens of millions of years, but considering the lackluster evolution in the billions of years before, this was a monumental event.

Scientists still argue over the cause of the Cambrian explosion. It was already mentioned that some of those original, simple organisms started producing oxygen. Well, one theory is they rapidly multiplied, increasing oxygen levels substantially and allowing for new, more intricate life forms to emerge. These preyed on lesser life forms and kickstarted the evolutionary arms race that would go on to define the development of life on Earth forevermore.

Regardless of how it happened, the Earth was now perfect for these new breeds of life. The average temperature was much warmer than it had been, with waters likely to have been around 110 degrees Fahrenheit! This, alongside extra oxygen and carbon dioxide, gave life the opportunity to level up, and level up it did!

The Cambrian Period

Eyes, limbs, mouths, exoskeletons, shells; these adaptations all started around this time. Though, many of the animals that sported the upgrades were still completely alien looking!

Take trilobites. These creepy looking shelled arthropods could suddenly be found all over the ocean munching on plankton, scavenging on scraps, and hunting other animals. You might recognise them from the abundance of fossils that still remain today. Indeed, trilobites were some of the most successful animals to ever live, thriving for hundreds of millions of years.

But they weren’t the only things that appeared during the Cambrian. The very first fish would also show up. They started out as slimy, jawless eel looking things. Crucially, this marked the moment the first true vertebrates evolved. Not that they were exactly impressive in the beginning.

Yunnanozoon was a weird worm looking guy that possessed a backbone despite looking utterly spineless. Other animals of the Cambrian were even weirder, like the utterly freakish Opabinia, a bottom feeder that looks like it was designed by a child. It’d use that long beaky thing to pick up tiny prey items and place them directly into its mouth.

Opabinia regalis - Creature of the Cambrian Explosion by Paleozoo

But with predator and prey dynamics becoming firmly established, one animal needed to stand, or swim, above the rest. The Anomalocaris, meaning abnormal shrimp, was the top predator of the day. A little over a foot long, which was huge for the time, this nightmare prawn patrolled the oceans, devouring soft bodied animals like worms.

Anomalocaris Cambrian predator by Paleozoo

Now, with such a peerless predator on the prowl, animals were forced to adapt even more to survive. The evolutionary arms race had just been kicked up a notch! Or at least, it should have been.

Around 485 million years ago, just when it looked like everything was coming together and life was steadily advancing, disaster struck. It’s still a mystery as to why, but it seems that a dramatic drop in oxygen levels, possibly caused by volcanic activity, led to a mass extinction event.

Not everything was wiped out. Some creatures like our old pals the trilobites carried on thriving but the event was undoubtedly apocalyptic in scale. The Cambrian period was officially over, and the Ordovician period was about to begin.

The Ordovician Period

The Ordovician has been largely defined by the Great Ordovician Biodiversification Event, aka the GOBE.

Over the course of some 30 million years continents shifted, sea levels fell, and oxygen levels in the ocean increased again. The shifted continents created new islands, which birthed segregated habitats in the freshly oxygenated waters around them. Habitats that were ripe for conquering. And life was up to the challenge!

Prototype fish continued to evolve into increasingly more “fish” like shapes, though they still had a long way to go before they’d become anything like Nemo. Elsewhere, more nightmarish beasties were emerging. Meet the eurypterids, or sea scorpions.

These predatory arthropods weren’t actually scorpions but are colloquially referred to as such. Why? Because of their long spiked tails, grabby claws, and the fact that they’re horrifying. Seriously, the earliest, Pentecopterus, could reach pant-wetting lengths of over 5 and a half feet. Add these to the list of things you can be glad are long dead.

As scary as they were though, they weren’t top of the food chain. That honor goes to Cameroceras, a predatory cephalopod related to modern octopuses and squids.

Cameroceras could reach a terrifying 23 feet in length, shell included, and would scour the depths for arthropods like sea scorpions to snack on! Their sharp beak was more than strong enough to crunch through hard exoskeletons and shells, making it top dog in a world filled with armored Hors D'oeuvres!

But fauna wasn’t the only thing that was changing, flora was about to take over the world. Primitive algae had existed in the seas since the Cambrian, but it was nothing to write home about. That is, until the Ordovician kicked things up a notch.

Algae evolved and spread onto dry land for the very first time as moss, sort of dry land. These early migrators lacked roots and other specialized parts needed to retain water without help, so they dwelled on the edges of waterbodies where it was damp.

Despite such humble beginnings though, this was the start of nature’s conquest of land. Not least because plants began absorbing carbon dioxide from the atmosphere and releasing oxygen into it. A journey that would one day lead to the creation of Denny’s.

The Ordovician period came to an end around 443 million years ago with another mass extinction; this time caused by an ice age. There’s actually been a fair few of them throughout our planet’s history. Each one has been utterly devastating, and this was no exception.

Beginning 460 million years ago and persisting for the next 40 million years, glaciers enveloped the southern hemisphere, cooling the entire world and crippling marine animal populations worldwide.

Though all the main animal groups survived, their numbers were drastically reduced, and many major species, like Cameroceras, didn’t make it at all. In fact, some 85% of all marine animal species were wiped from existence.

Interestingly, some scientists blame this calamity on the success of the new land-dwelling plants. They claim the moss absorbed so much carbon dioxide from the atmosphere that it had a cooling effect on the planet, eventually causing the full-blown ice age. However it happened, one thing is for sure, the Ordovician was over, and the Silurian had just begun.

The Silurian Period

40 million long years after it’d formed, the ice finally dissipated as CO2 returned to the atmosphere. The melting ice caused sea levels to rise and the climate eventually stabilized, allowing life to expand again.

And with the Cameroceras gone, sea scorpions were free to rise to the coveted rank of apex predator. Thriving more than ever before, they diversified and got even scarier. The Carcinosoma, an unusually massive eurypterid grew to over 7 feet in length.

Fish too continued to adapt. The first piscine with movable jaw action made its appearance in the Silurian period. And the very first coral reefs emerged as well! These formed important parts of diverse new ecosystems and played host to the hardy trilobites and other creatures.

Meanwhile, the terrestrial plant life that may or may not have just wiped out most other life on the planet was going from strength to strength. Plants on land began to take on far more complex, recognizable forms, and evolved into vascular, stemmed organisms that could absorb and retain water self-sufficiently.

These plants would form the basis for all modern flora, and with them came the next wave of oxygenation for the Earth’s atmosphere. This time, rather than plunging the world into an ice age, quite the opposite happened. The additional oxygen proved enough to support animal life on land!

Arthropods began to crawl out of the oceans, with the very first groups probably being myriapods like centipedes and millipedes, and arachnids, like scorpions. These creepy crawlies may have initially only left the water to avoid predators or access new food sources, but the prospect of a whole new environment to conquer proved too good to pass up.

Life was super competitive in the ocean. The land however was a new, unconquered playground of opportunities. Not that every species that ventured out immediately lost their gills and learned to breathe air. Silurian scorpions still had gills even after moving onto land and had to keep them moist to function. So, they wouldn’t have strayed too far from the water’s edge, at least not at first.

The Silurian period met its end around 419 million years ago with some relatively minor extinction events probably caused by the changing climate. It's “relatively minor” because unlike others, they didn’t bring the entirety of life on Earth to its knees and threaten to make the planet totally lifeless again. They weren’t exactly fun though.

The Devonian Period

The Devonian period is what followed the Silurian period, and it would prove the most influential period of life since the Cambrian! For a start, the earliest known sharks evolved, though they were far from the top predators we know today. In fact, they were completely overshadowed by a group of bony fish called Placoderms, like the absolute beast Dunkleosteus.

Old Dunkly was the apex predator of the day. At its smallest estimate, it was a little shorter than a male great white shark. That’s three times the size of an adult human! But at its biggest, it was equal to several great whites put together, at an astronomic 26 feet!

Without a doubt, this was the biggest species alive at the time, and one of the most intimidating fish to have ever lived. Its colossal head housed guillotine like teeth and experts reckon it had a stronger bite than a saltwater crocodile! For context, saltwater crocs have the most powerful bite of any living creature, but Dunkleosteus had more than double that.

Fish weren’t the only thing getting super-sized either. On land, plants started bulking too. The culmination of all prior evolution, the very first wooded trees sprang up with complex root systems, branches, and height.

They formed the original forests, which produced a whole load more oxygen for the atmosphere while absorbing huge amounts of carbon dioxide. All this meant the terrestrial ecosystem became even more inviting for new life. And so, finally, the vertebrates took notice.

Certain species of fish, like lungfish, had been spending more and more time in shallow waters, and some had even flopped onto land for brief periods. But in the Devonian, everything changed. They evolved. The most interesting representation of this is Tiktaalik, the earliest known vertebrate that could breathe out of the water.

This freaky looking fella had characteristics of fish, amphibians, and reptiles, a bizarre middle ground between the worlds of land and sea. While it still lived mostly underwater, it was capable of clambering onto land when needed.

And then we have Ichthyostega, one of the first tetrapods, animals with four fully fledged limbs, like us! Though they too spent most of their time in the water, the world would never be the same again.

Meanwhile, the arthropods that were living on land already started to diversify. Wingless insects and spiders developed and spread. For those creatures still confined to the seas though, things were about to get a whole lot worse.

As the Devonian period neared its end, oxygen levels in the oceans began to decline harshly. Without the oxygen to keep them alive, immense swathes of marine creatures died out. The long-lasting trilobites and sea scorpions were decimated, and although some survived, their populations would never recover.

Dominant species like the Dunkleosteus on the other hand were completely eradicated, and up to 70% of all invertebrate species died out. We aren’t entirely sure what caused the sudden drop in oxygen, but scientists reckon it probably involved trees. Trees in this era reached up to 130 feet tall, so needed deep systems of roots to support them.

But roots don’t just anchor plants and absorb nutrients; they also affect the earth around them, altering rocks and creating nutrient-rich soil. This soil covered the planet so thinly that much of it washed off into rivers and oceans, taking all its nutrients with it. This fueled a series of huge algae blooms in the water, and as all this new algae photosynthesized, it removed oxygen from the water. Not good for anything living in there.

Who knew that plants could be responsible for so many deaths? While life underwater was devastated however, the land dwellers continued to thrive, marking a palpable shift in the balance of power. The era that came next, the Carboniferous era showcased the sheer dominance that life on land had cultivated.

The Carboniferous Period

Starting 359 million years ago, the Carboniferous period saw terrestrial plant life flourish and multiply even more, forming vast jungles and murky swamplands that covered most of the planet. This incredible amount of foliage caused the oxygen in the atmosphere to reach levels completely unheard of before or since.

And it had some crazy effects on the animals of the day. Remember the arthropods that first invaded the land back in the Silurian? By now they’d had a very long time to evolve and adapt, and they were everywhere. When the oxygen in the air skyrocketed, they were given their latest upgrade.

Arthropods take in oxygen through small holes in their body. With more oxygen up for grabs, and huge amounts of available food in the form of these new plants, they grew absolutely enormous.

Take the Arthropleura, a millipede the size of a car. Seriously, this thing could’ve reached a terrifying 8 and a half feet long! Fortunately for any smaller critters around at the time, millipedes have always been vegetarians.

NEW CLIP | Arthropleura - The Giant Millipede (Life On Our Planet) by BestInSlot

Not that many critters were exactly small, even among those with wings. The aptly named Meganeura was one of the largest flying insects to ever live, with a wingspan of 2.5 feet. That’s about the same as an American crow! The tetrapods also exploded in diversity, both on land and in the water. The early amphibian Diplocaulus evolved in this era and was a complete weirdo.

This 3-foot-long freak sported a strange boomerang shaped head that experts suggest could’ve helped it to glide through the water or deter predators. It’d be hard for anything to swallow this guy! But it was outside of the water that the tetrapods made their next giant leap. No matter how much time they’d been spending on land, they were still forced to return to the water to give birth.

That was, until an incredible evolutionary adaptation changed everything! Terrestrial tetrapods started laying eggs with hard shells. These fancy new eggs were able to keep amniotic fluid inside their walls, negating the need to be laid directly in water, and the shells also protected the young inside from predators.

With that, tetrapods would uncouple themselves from life in the water for the first time ever. These were the very first amniotes, the ancestors to most modern land animals! It's pretty lucky that the tetrapods developed this amazing adaptation when they did because the end of the Carboniferous period would change the planet entirely, again.

Earth’s various land masses had been gradually shifting over the preceding millions of years, until around 335 million years ago they all collided together and formed one super continent, Pangea. But what exactly did this mean for life on Earth? The lush rainforests that covered the planet suddenly found themselves struggling. They became fragmented and scattered, and the formation of the supercontinent meant trees that once had access to copious water now found themselves inland and quickly dried up.

This destroyed habitats and consequently lowered the incredible oxygen levels in the atmosphere. Couple this with dropping temperatures and a wave of oncoming glaciation, and the rainforests were done for.

The formation of Pangea had started a domino effect that brought the Carboniferous period crashing down around 299 million years ago. In its wake was a much drier, less forested world largely unrecognizable to what had come before. Many species went extinct due to this massive climate change, including the giant arthropods who relied on lots of oxygen.

But the amniotes stayed strong. With no need to return to water to reproduce and a scaly body to prevent water loss, the stage was set for them to take over the world. Split into synapsids, the group that would become mammals, and sauropsids, the group that would evolve into reptiles and birds, it was all coming together.

The Permian Period

The next era, the Permian, began with a rise in temperature. The glaciers that had formed at the end of the previous period slowly melted away, with the most inland areas becoming dry deserts. And the supercontinent would only get hotter as the period went on!

Life was difficult, so the animals that thrived were the ones capable of conserving water most effectively. Enter the synapsids and sauropsids! These guys had diversified and spread across Pangea, becoming the dominant land animals. But it was the synapsids that truly ruled the Permian. They were slowly but surely evolving and becoming more like mammals.

Dimetrodon was one such creature, a big mean boy. Probably the most iconic animal of the time, this thing was so menacing that it’s often misconstrued as a dinosaur! In reality, it’s more closely related to us humans. It was the top predator of the early Permian, reaching intimidating lengths of 15 feet!

Consensus is still split when it comes to what that big old sail was used for. Some scientists say it helped regulate body temperature, while others believe it was used to attract potential mates. Despite enjoying great success, Dimetrodon did eventually die out though after its 16-million-year tenure. Taking the crown as the middle to late Permian’s apex pred was another group of synapsids, the Gorgonopsians.

These ugly mugs weren’t as big as Dimetrodon. The largest species, Inostrancevia came in at only 11 feet long, but they were deadly. Gorgonopsians had a mouth filled with six-inch-long, saber like canines, probably used to shear the skin off their prey.

That’s freaking terrifying and they’d have turned these teeth on animals like the lumbering sauropsid Scutosaurus, slow, armored herbivores that had to walk for miles to hunt down scant vegetation.

But enough of the lame Scutosaurus. The Permian era also gave birth to the greatest animal to ever live. Let me introduce you to the Cotylorhynchus! It had a tiny little head with no neck at all. And it was an adorable plant munching freak.

But don’t get too attached to him. Remember when it was mentioned that the Permian would only get hotter? Over the course of a million years, a series of extensive volcanic eruptions began to tear through what is now Siberia. These eruptions spread unbelievable amounts of burning hot lava across the planet. You can picture giant lava beds half the size of the United States, all spewing colossal amounts of carbon dioxide into the atmosphere.

All this CO2 trapped heat within the ozone layer, raising the Earth’s temperature dramatically and forcing animals to adapt or die. Marine animals fared no better than those on land. The ocean absorbed some of the carbon dioxide, making the water dangerously acidic.

Then, the hotter temperatures ignited wildfires on land that burned down what foliage remained, incinerating forests and exposing previously hidden rocks. These quickly eroded and the nutrients left behind ran off into the ocean, unwittingly causing an explosion of life.

While it seems like things all turned around, that wasn't the case. Actually, the overwhelming number of new lifeforms turned out to be less a blessing and more of a curse. They absorbed what little oxygen remained in the sea, suffocating any creatures that had survived the initial onslaught.

By the end of the Permian around 251 million years ago, this apocalyptic event had reached a fever pitch. Since termed the Great Dying, it was the single most devastating mass extinction the world has ever seen, and the closest life has ever come to disappearing entirely. A shocking 70% of land animals and 90% of sea creatures were wiped from the face of the Earth.

The tiny number of beasties that survived these end times were left with a husk of a world. All the periods of prehistory we’ve covered so far are grouped into an overarching era known as the Paleozoic, meaning ancient life.

With the Great Dying, it wasn’t just the Permian that ended, but the entire Paleozoic with it. That’s a nearly 300-million-year span. But history didn’t just end. Life went on! The Mesozoic was here, the era that would eventually herald the arrival of the dinosaurs. But not quite yet.

The Mesozoic Era

The Mesozoic era began far more humbly, with the Triassic period, the first 5 million years of which life spent slowly recovering to the point new dominant species could emerge again. This new world was a supremely difficult place to live, and the few species that stood a chance would need to be pretty darn resilient.

Most of the synapsids, sadly, didn’t have what it takes. They were utterly devastated by the Great Dying and, though a handful did survive to eventually evolve into modern mammals, they’d take a backseat for a long time. The sauropsids on the other hand, were perfectly suited!

Given their ability to survive away from water due to their hard-shelled eggs, and retain moisture with those scales, they not only recovered, they utterly dominated the planet. Indeed, the Triassic saw sauropsids diversify and evolve at a rapid rate never seen before.

Some took to the empty oceans, evolving into the very first marine reptiles, like Ichthyosaurs, bizarre and terrifying fish-like beasts that hunted using some of the largest eyes in the animal kingdom.

Ichthyosaurs 101 | National Geographic by National Geographic

Alongside them, the plesiosaurs would eventually patrol the seas too. These equally bizarre creatures had monumentally long necks that could’ve helped them hunt more stealthily. Both marine reptiles would thrive for hundreds of millions of years.

Other creatures, like the strange Drepanosaurus, evolved to live in trees, possibly acting similarly to modern lemurs and sloths and hanging from their tails. Like an aye-aye, Drepanosaurus had one super long claw for poking around inside insect nests attached to tree branches. So, yes, this thing was essentially a monkey lizard.

But trees weren’t the final frontier for these newly evolved reptiles. Some began to evolve flight! To start with, this took the form of some weird experiments like the Sharivopteryx. Unlike pretty much every flying animal we know of, this little reptile had wings on its hind limbs instead of its front.

Because of this, it couldn’t actually fly, instead, it was only capable of a sort of clumsy glide. Unsurprisingly, this design didn’t carry through to modern day. By the tail end of the Triassic however, this evolutionary trait had been perfected with pterosaurs. Hollow, air-filled bones meant these sky bound reptiles were light enough to sustain flight, and their wings ran all the way from their forearms, across the lengths of their bodies, to their ankles.

Now that we’ve covered the sea and the sky, what was happening back on dry land? With the once dominant synapsids largely extinct, the sauropsids there had evolved into a new sub class known as archosaurs to take their place. And they were super successful.

Archosaurs had a very efficient respiratory system that allowed them to survive in harsher conditions. Oxygen was probably in limited supply during the Triassic due to the sheer amount of CO2 in the atmosphere after the Great Dying. So, this superb respiratory system allowed archosaurs to excel where other species couldn’t.

But that’s not all! Archosaurs also made rapid progress towards upright limbs! It might seem like a stupid thing to get excited about, but it granted them a big advantage. Tetrapods with limbs that stretch outward, like modern lizards, move by flexing their bodies sideways. This shunts stale air from lung to lung rather than expelling it to make room for fresh air, making it impossible for them to breathe and walk at the same time.

But with upright limbs? Not a problem! Archosaurs had it covered. One particularly formidable member of the group was the horrifying Postosuchus, a 15-foot monster that ruled as apex predator. This fanged fiend resembled a cross between a T-rex and a crocodile, a terrifying combo that nobody needed. Least of all the poor creatures it would prey on, which was pretty much everything.

Experts reckon Postosuchus stalked its prey on all fours, but when close enough could’ve risen up onto its hind legs to bite into their neck or spine. In fact, it was so fearsome that when dinosaurs did finally come into the fray, Postosuchus firmly held its own. Archosaurs took over the world alright, but in the middle of the Triassic, there was one more advancement that turned the planet on its head.

There, in the wastes, appeared some seemingly unremarkable breeds of archosaur. Unremarkable however, they were not. These were the very first dinosaurs. With all the advantages of their brethren, as well as an incredibly fast breeding rate, they were set to conquer the globe and usher in a new age.

I hope you were amazed at the evolution of life on planet Earth before the dawn of the dinosaur age! Thanks for reading.