From cyanobacteria to fungi.  Dinosaurs and chickens. Whales and cows. Monkeys to humans, the evolution of life is a story with surprising twists.

Earth has been home to over five billion different species of organisms. Of all of those living life forms, an estimated 99% of all species are now extinct. We, humans, are currently sharing the earth with about 12 million other species.

So how did it end up this way, and who lived before us?

In this article, we’ll outline the timeline of life on earth. Our planet’s evolution started with the first organism ever to call our planet home.

What was the first form of life on Earth?

The timeline of life on earth begins over 4.5 billion years ago. In the beginning, survival was difficult for any life forms. The struggle started and soon after earth’s formation, organisms start appearing.  It makes sense the first signs of life on planet earth are incredibly simple.

The earliest fossil evidence of life on earth dates to 3.7 billion years ago. They were found preserved in ancient rock samples from Greenland. The fossils were once part of a now-extinct seabed and thought to be the remains of ancient microbes.

These anaerobic organisms lived in the absence of oxygen. They process the other chemicals that were abundant in the early atmosphere and oceans. The efforts of these microbes created the conditions for all other life to evolve across the earth.

How did photosynthesis change the earth?

2.1 billion years ago more sunlight was starting to penetrate the earth’s toxic atmosphere.

Cyanobacteria, named after their blue/green color- were the first to start exhaling oxygen. Here the early stages of photosynthesis began.

For more than a billion years, the timeline of life on earth existed in primal forms. All life was single-celled organisms, made up mainly of bacteria and algae.

When did life first evolve?

It’s unknown why, but around 900 million years ago simple multi-celled organisms started to appear. They evolved from simpler organisms to have different types of cells with individual functions.

Here was a critical period of the evolution of planet earth. These newly formed organisms would evolve into all forms of life on earth today.

What started the Cambrian Explosion?

540 million years ago a mysterious event occurred. Suddenly, and seemingly out of nowhere, large numbers of species started appearing. It’s a period is known as the Cambrian explosion.

In the Cambrian, the first-time animals with mineralized skeletal systems lived. On a scale of evolution, this period in the timeline of life on earth was by far the most exciting and vital.

Soon after, the first vertebrates appear. Then the emergence of life on to land rather than confined to the oceans. Corals, ancient shelled organisms, mollusks, soft bodies life forms, all began developing at this time.

The evolution of diverse life on earth

After the Cambrian explosion, life on earth was climbing in diversity. Many new species of plants and animals separate onto a path of evolution. New forms of life began to appear.

Plants began colonizing the land, and fish began swimming in the seas. The first life on land started as algae gradually adapted to be able to live on dry land.

Around 400 million years ago, the first four-legged animals started to develop. These animals, known as tetrapods, are the ancestors to all birds, mammals, reptiles and even amphibians.

The first amphibians appear soon after, living on sea floors and in shallow marine ecologies. They were the first species to branch off from the tetrapods.

Insects are next, although they took some time to develop wings.

Then reptiles developed in swamps and tropical forests, which were mainly made up of ferns and other ancient coniferous plants.

What was the first predator on earth?

At 300 million years ago, many species were living in many ecologies. Reptiles especially thrive both on land and in water.

The first aquatic reptile to exist was known as a Mesosaur. It preyed on amphibians and other sea creatures. Scientists don’t know why this ancient predator diverged from its fellow reptiles and returned to the ocean.

The most well-known land-dwelling ancient reptiles were the Dimetrodon. This early predator had an appearance much like a dinosaur. However, the last remains of a dimetrodon have been dated to 40 million years before dinosaurs walked the earth.

The Dimetrodon was one of the first predators to evolve on planet earth. Source

When did the first dinosaurs appear on Earth?

250 million years ago marked the first emergence of dinosaurs. They were pre-empted by a mass extinction event that shattered all life on earth. Around a third of life on planet earth was wiped out, marking a huge fork in the timeline of life on earth. Yet, as life has shown to do throughout history, it continued on living.

The dinosaurs weren’t initially the dominant species on the planet. It would take 50 million years to take over the entire planet.

When did the first mammals appear on planet Earth?

In the late Triassic, 200 million years ago, the first mammals appear. It was soon after the dinosaurs became the dominant species on earth. These mammals were very small, many no larger than mice. Here the first warm-bloodedness mammals appear in the record. In the timeline of life on earth, mammals began splitting into the four major groups that can be observed today. It’s not known why it happened.

Today, it’s unknown exactly when, but around this era saw the emergence of the first birds. They are thought to have split from dinosaurs or reptiles. How and when is still a mystery.

As all of this was unfolding in the animal kingdom, plant species across the world were diversifying rapidly. The first signs of flowering plants are linked to this time as the evolution of the planet flourished.

During which era did the dinosaurs become extinct?

66 million years ago saw the Cretaceous-Tertiary extinction event. It was the mass extinction that saw dinosaurs wiped from the face of the earth. It meant that mammals, which were previously living in the shadow of the dinosaur, could take over and dominate the land. They started small, but quickly grew and diversified, enjoying their new dinosaur-free world.

It was around this time that primates began spreading and diverging into new species. Lemurs, gibbons, bonobos, orangutans, gorillas, and even modern humans are all linked to this point in the timeline of life on earth.

Around 50 million years ago, whales evolved to live under the sea. The earliest forms of these are thought to have been land animals adapting to life in the sea. They began by returning to the land only to give birth.

What are the Pleistocene megafauna?

Over the next few million years, evolution continued among mammals. For reasons unknown, many species started getting bigger and bigger, some growing to enormous sizes.

These animals, known as megafauna, populated the planet up until around 10,000 years ago when unknown events wiped most of them from the face of the earth.

Some incredible megafaunal species include:

• Mammoths
• Wooly rhinoceros
• Giant beavers
• Giant ground-sloths
• Sabretooth tigers
• Glyptodons
• Megalodon
• Daeodon
• Short-faced bears

Earth’s series of extinction events culminates around 10,000 years ago. It is called the Younger Dryas Extinction Event. Today most of the remaining megafauna living on the plains of Africa.

Conclusion:

Despite all the species we know have lived and existed, many are found every day. Millions more are thought to remain undiscovered.

Today humans are the dominant species on the planet. Our footprint means many organisms are becoming extinct. One challenge of humans to fit into the timeline of life on earth see how it would look if we were to vacate the planet and let nature take back control.

What other animals lay on the depths of the sea or in the far reaches of the globe is anyone’s guess. Whatever they are, they all make up the abundance of life on earth.

Now it’s up to you. How does the timeline of life on earth impact our lives today? Can we reshape our habits to better in tune with planet earth?

Leave your thoughts in the comment section below.

Further reading:

1. https://www.livescience.com/55950-worlds-oldest-fossils-found-in-greenland.html
2. https://www.newscientist.com/article/dn17453-timeline-the-evolution-of-life/
3. https://burgess-shale.rom.on.ca/en/science/origin/04-cambrian-explosion.php
4. https://www.newscientist.com/article/dn17453-timeline-the-evolution-of-life/

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For nearly 4.5 billion years the story of earth goes. Through much of its lifespan, the planet looked vastly different than today. In its early life, there was no water, no oxygen, no land, and no life.

The earth then formed in violent circumstances. Its earliest period remained chaotic and semi-apocalyptic for millions of years. The planet was molten hot and bombarded with incoming objects from space. In these early episodes of earth’s life was during the time the planet itself was still taking shape.

Let’s explore the story of earth.

How did the atmosphere form around the Earth?

About 4.1 billion years ago the planet began to settle down. It was then that time earth locked into an orbit around the sun. From here the surface began to cool down slightly. It was around this time that the first atmosphere started to take shape.

Unlike the fresh air we enjoy today, early earth’s atmosphere was unstable and poisonous. Made of elements like nitrogen, sulfur, hydrochloric acid, some water vapor and carbon monoxide among others.

It wasn’t until the planet began to cool off slightly that the atmosphere began to stabilize. Water, previously vaporized, was able to take a liquid form and the result was oceans spanning over the entire planet.

As this was happening, intense volcanic eruptions disturbed the earth, and huge clouds covered the skies, meaning rainfall and more cooling.

When did land first appear on Earth?

In the next stage, rocky terrain began to form. The atmosphere started to mix and steady. Now the first signs of life appear as simple bacteria. Evidence of these creatures are the only real evidence scientists can use to gauge this period.

For around 1 billion years microbes would be the only form of life that could survive the toxic atmosphere of earth.

Landmasses continued to grow as volcanic eruptions spat out molten lava that would become rock, and the earth slowly took on an appearance more like today.

When did oxygen appear on Earth?

Around 2.5 billion years ago, oxygen appeared. As more sunlight was able to penetrate the earth’s atmosphere, it brought the first opportunity for photosynthesis.

Oxygen formed made by simple blue-green algae known as cyanobacteria. They are thought to be the first oxygen creating organisms to live on earth. The air we now breathe is all due to these tiny microbes.

It was over the next billion or so years that things began to move along. Earth became more and more stable, with more photosynthesis filling the atmosphere and oceans with oxygen. Levels rose, although atmospheric oxygen was still as low as 5%.

Rodinia the first supercontinent

As oxygen rose, continents were starting to appear. It was the time that the first supercontinent ‘Rodinia’ took shape. Up until this point, the earth was made up of as much as 95% water.

Life on this supercontinent wasn’t very advanced.  Simple algae and bacteria were thought to be the only organisms to live there. Violent conditions made life on earth difficult. Storms plagued the land alongside intense radiation and floods.

Around 350 million years later, heat and pressure building beneath the continent hit critical mass. The crust below Rodinia ruptured, and the first great supercontinent was no more.

Pangaea the next supercontinent

After Rodinia broke up and drifted apart, oceans formed between the new landmasses. Over time, the land changed its course and was brought back together forming the supercontinent Pangaea some 225 million years ago.

The seven continents that make up earth today are remnants of Pangaea. One day, millions of years in the future, the continents will drift back together, and a new supercontinent will form.

What were the first forms of life?

The bacteria that increased oxygen levels were creating a less toxic atmosphere was born. Complex life began to evolve, and single-celled organisms began to develop around 1.5 billion years ago.

Eventually, these simple life forms split and began to evolve separately. All animals, plants, and fungi trace back to this time. It’s difficult to pinpoint what order and the exact way this occurred.

When did multicellular organisms first appear?

Around 900 million years ago multicellular life evolved. It’s unclear how, but it did, and it took millions of years to happen.

After a slow start, the evolution of life on earth began to speed up.

The oceans were home to lots of varied forms of life. Sponges, simple jellyfish, ancient worms, starfish, and coral, all began to appear after splitting and evolving separately from their multi-celled ancestors.

New species and organisms flourished under the oceans then making their way onto the land.

Around 500 million years ago that the first organisms set foot upon the earth’s surface. The massive step in evolutionary terms began the process for plants and trees to develop. The oldest fossilized tree remains date to 385 million years ago.

Four-legged animals followed soon after. Then fish, reptiles, ancient mammals and amphibians.

Cataclysmic cycles and the evolution of life

Throughout earth’s history, life is interrupted by great cataclysms that rock the very foundations of the planet. Meteorite and comet impacts have nearly wiped out all living things. One of these events rocked the earth 250 million years ago, causing the first great mass extinction event.

It paved the way for new organisms to take over where their extinct ancestors left. After this extinction event, it was the dinosaurs to populate the earth. They were the dominant species on the planet for millions of years, growing to enormous sizes. The largest known animal to ever walk the earth lived during this time, known as the giant sauropod.

As dinosaurs were at the top of the evolutionary tree, another cataclysm rocked the earth. Sixty-five million years ago saw the once dominant animals reduced to nothing but fossils. From this point on mammals became the dominant species on the planet.

It seems incredible how life can bounce back after a disaster. These cataclysms have proven to be vital in the evolution of species on the planet.

When did humans first appear on earth?

Here the story of earth gets very complicated. By now, life is very diverse across the globe. There are many opinions and ideas concerning the first humans, their evolution and spread over the world.

It is agreed that our earliest ancestors diverged from chimpanzees sometime around 6 million years ago. There some say this number may vary between 5-7 million years.

Sometime after that, the earliest hominins began walking on two feet, and our ancestors started the evolutionary journey towards modern humans.

Conclusion

The story of earth begins 4.6 million years ago and takes a journey of difficulty and resilience.

Today most of what we know is a scientific guess. In the coming years it’s likely we will see this story change.

We can thank our lives today for the process of planet earth.

Now it’s up to you. What will we learn of the way our earth formed?

Leave your thoughts in the comment section below.

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Planet earth is 4.6 billion years old. That’s a very big number.  It is one of those numbers that you hear people say, yet it’s hard to even picture. There’s not enough time to even count that high within a single lifetime.

If the earth age dates to this period, exactly how did the earth form? A look at the origins of our planet reveals a chaotic time as far back as we can imagine. These events eventually settled, and luckily for us, life began to develop and prosper everywhere across the globe.

In this article, we’ll explore the question: How did the Earth Form?

Who discovered the age of the earth?

Finding the age of a planet isn’t as complicated as you might think. Caltech geophysicist Clair Patterson was the one to settle the debate. The process is as simple as finding the oldest piece of the planet, then dating it. So it’s fair to say that 4.6 billion years is the age of the earth we know today. It could change if an older rock surfaces.

So far, the oldest sample found on earth has dates to 4.3 billion years old. It is an ancient zircon rock uncovered in Australia. With room for error in the dating, scientists have come to agree that 4.6 billion years is a good approximation for the earth’s age. Although it’s a big number, it could be much older than that.

The land before time

Before the formation of the earth, the solar system, and even the sun, scientists believe there was only clouds of dust particles whirling around.

What transpired after this is still debated. Two main theories on the earth’s origins are still openly discussed today. Which is correct? The truth is we don’t know.

The core accretion model of how the earth formed

Currently the accepted model on how the earth and planets in general form. Before the earth, sun and solar system were around, only tiny particles of space dust and debris were present.

Something then happened to disturb these particles, possibly the explosion of a nearby star, and as a result, the sun was born. The immense energy created caused the clouds of space dust to go into a high-speed spin.

With all these particles whirling around and crashing into each other, many began to collide under unbelievable pressures. They eventually formed our star, the sun. The newly formed sun created a powerful gravitational pull that it drew the dust cloud into nearby orbits.

As the small particles began to collide, they, in turn, became larger particles. As this was unfolding, extreme solar winds blew away lighter elements such as helium and hydrogen, meaning the denser and rockier materials were left behind in a battle of space objects. Earth and other large planets formed as the objects became increasingly large.

Because the heaviest elements sunk to the center of the newly formed planet, the core became the densest part. It left the lighter elements to rise to up, and the earth’s crust formed.

How the atmosphere formed

The early atmosphere is thought to have formed as outgassing, and incredible volcanic activity continued across the planet. As these primordial times were fiery and turbulent, there were constant collisions with the newly formed earth and other objects in space.

Through collisions, much of the water was delivered to earth. Enormous icy bodies in the form of comets entered the atmosphere and cooled the planet. They also brought the building blocks of life as we know it.

It was all possible due to earth’s distance from the sun. A distance known as the ‘Goldilocks zone.’ The water hurled into the atmosphere didn’t freeze or evaporate; it was able to remain liquid and eventually formed the earth’s earliest oceans and rivers.

The disk instability model of how the earth formed 

A relatively new in an attempt to answer the question: how did the earth form. Unlike the intense collisions necessary in the core accretion model, this theory doesn’t require them at all.

Based on the idea that after a new star forms, gas and dust begin to clump together. These bound particles begin an orbit of the newly formed star and gradually condense into planet-sized objects. Almost as if the planet forms from the outside in rather than the inside out.

These clusters form naturally in space and are like small communities of space particles. They go through a process of slowly compressing into themselves. The resulting planet is generally thought to be massive and entirely gaseous. It is then possible for them to become rocky and earth like if the conditions are just right.

The bundles of gas and dust have banded together. It means there is a large enough mass to save them from being sucked into the molten star that has just formed.

The theory also has a different timeframe. Formation of planets within the disk instability model would have to occur in a much quicker time (possibly only a few thousand years). It suggests lighter gases that would otherwise escape, to be trapped as the new planets form.

Which theory is correct?

Each explanation does enough to explain how specific planets form. However, they both fail to allow for the creation of every size and type of planet visible in the universe.

One of the main problems with the disk instability model is that it only explains huge planetary bodies that are gaseous, like Jupiter.

It has been difficult for the advocates of the theory to explain how the earth could have formed this way.

The core accretion model fails to logically describe how huge gaseous planets are created at all.

It also doesn’t explain tiny planets found throughout the universe. With prolonged processes in core accretion, smaller planets wouldn’t have enough mass to orbit the new star. They would instead be sucked in and consumed by it.

Conclusion

So how did the earth form? The answer may be one of these two theories or a combination of both. Either way, they are accepted and have been observed in some way or another in modern times.

Maybe it’s the just too long ago to know for sure, or perhaps we have already had the answer but can’t prove it yet.

Whatever the case, the origins of the earth continue to be discussed and keenly researched by scientists across the globe.

Now it’s up to you. How do you explain the formation of planet earth?

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