The History Of Life On Earth

Is a long and complex affair dating all of the way back to the very beginnings of our planets creation. From the formation of our very first oceans to the first amounts of oxygen that appeared in our planet’s atmosphere during the “Great Oxidation Event”. The Earth has gone through several periods of evolutionary that took place over millions upon millions of years. To get a sense and feel of what our planet was like and to see how it became the way it is today lets dive deeper and take a look into the history books and witness the history of life on Earth.

Our Earth is estimated to be around 4.5 billion years old. The early Earth at first was a hot mass of gasses with no oxygen or water making the planet we inhabit drastically different from the one we know today.

While there is no clear answer as to how our planet first obtained water scientists theorize that comets first brought water to Earth when they bombarded the surface of the planet.

At first it may sound surprising to hear but in fact “Both comets and asteroids contain ice. And if, by colliding with Earth, they added the amount of material some scientists suspect, such bodies could easily have delivered oceans worth of water.” To summarize this means that the ice the comets and asteroids were carrying was melted and there was a large enough quantity to form our very first oceans! This was the beginning for our planet ton make its next leap forward! Earth had no oxygen within its atmosphere making the planet extremely desolate and impossible to survive.

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But when ice from comets that came to Earth and melted into water the planet was about to undergo a major transformation.

The first life on Earth was blue-green algae much like the ones in our oceans today. They are single celled microorganisms and are the group that was the catalyst for a major event in Earth’s history known as the “Great Oxidation Event”. This event was the beginnings of the oxygen we breathe today. These organisms more or less created oxygen as a result of photosynthesis. Photosynthesis is the process in which all green plants get their food. The green plants we have today still use photosynthesis. The process of photosynthesis is when plants “Take energy from sunlight, and use it to make sugars out of water and carbon dioxide” (Marshall 2015). Oxygen is created as a result when the tiny microorganisms released it into the air. They do not need oxygen and pass them out like a person would pass gas. This event was a major time for Earth because without oxygen, ancient species would not be able to evolve to come on land and change the entire history of Earth.

The following time period in Earth’s history had a major development in the life on Earth was the Cambrian Period. During this period there was an explosion in many new species vastly different from the single-celled microorganisms from the period before it. This period is often nicknamed “The Cambrian Explosion as a result”. During this era we see the first appearance of creatures with shells on them. Some of these creatures looked similar to sea life that we have today like the “hard-bodied brachiopods, which resembled clams” (Bagley 2016).. There were also creatures called “arthropods-ancestors of spiders, insects, and crustaceans.” (Bagley 2016).. All life on the planet was about to undergo a major transformation at the beginning of the upcoming period that began following the end of the Cambrian Period.

The next major time period with a big evolutionary change in Earth’s history was the Devonian Period which was also known as the “Age of Fishes”. As the name suggests this was the era that fish began to make their mark as the dominant species of Earth at the time. The climate of the Earth was very warm during the period with the sea levels still high compared to the sea levels of today. Taking a look at the fossil record of this era we can see the types of fish that lived in this time. Some fish had armor and predators had jaws that could crush their prey. Looking in the fossil record we also see that fish appeared with gills, swim bladders, bones and teeth much like the fish we have today. Some of the first plants appeared during this period. Plants that had begun growing during early periods such as ferns grew larger than they were in pervious eras. Because there was such an increase in the number of plants during this era the amount of oxygen increased. This happened because plants like the blue-green algae discussed before, they create oxygen as a result of photosynthesis and they release it into the atmosphere. This was very important for the future of life on Earth as land animals would need the increase in oxygen to breathe on land.

Around 320 million years ago the Pennsylvanian Period began known as the “Age of Reptiles”. This era began when amphibious creatures that began to evolve into the more reptilian creatures that we have today. The overall climate during this era was generally more humid and tropical when compared to today with swampy forests covering the planet. This was the first environment that reptiles lived in. Many of these creatures were similar to the reptiles that we have today such as the first lizards and snakes that belong to a group called “Diapsids” and the group known as the “Archosaurs” that resembled crocodile-like creatures along with birds! The animals of this era became much more similar and recognizable to ones we have today. However in the coming future some of the most recognizable creatures in Earth’s history appeared ready to make their mark on the world.

The Triassic period began around 250 million years ago with many of the Pennsylvanian era reptiles evolving into dinosaurs. The dinosaurs of this era were much smaller than the ones people imagine from Jurassic Park but nevertheless became the same creatures we all know today. Evolution is a complex topic to discuss but the early reptiles of the Pennsylvanian era evolved into dinosaurs through adapting to new climates and surroundings of the era where it was more dry and easier for animals to live and evolve on land. The era of dinosaurs that dinosaurs began to be the dominant species was the Jurassic period with dinosaurs such as the Brachiosaurus which were long necked herbivores and the world-famous Stegosaurus. This was also the period in which the first birds began to develop.

Following the Jurassic period was the Cretaceous Period which occurred around 200 million years ago which had some of the most recognizable dinosaurs such as the Tyrannosaurus Rex, Triceratops and the flying dinosaur Pteranodon roamed the Earth. This period was unfortunately the period when dinosaurs became extinct. While scientists and academics are not one hundred percent sure as to what killed off the dinosaurs, common theories are that climate change was the culprit. The theories state that it was either natural cooling of the Earth or an asteroid strike that sent up debris that blocked out the sun and caused the Earth to cool. Whatever the case may be the Cretaceous Period was the period that marked the end of the era of the mighty dinosaur.

This was not the end of life on Earth however, as the age of Mammals was about to begin. Most early mammals were night dwellers because it was too dangerous for them to come out during the day in the era of dinosaurs as it was easier for them to be eaten as prey. The ancestors of Mammals were now able to come out during the day and forage for food and live without the fear of dinosaurs. With the age of Mammals, animals were able to diversify and after thousands of years we see some well-known mammalian species such as Wooly Mammoths, Saber Tooth Tigers and Wooly Rhinos begin to dominate the planet. During this time the first Homo Sapiens began to leave the plains of Africa and migrate all over the globe becoming the first Humans. Now Humans live in an era known as the Quaternary Period in which everything we know today takes place. Our continents settled in their current places and Humans became the dominant species on the planet after our ancestors began to discover technology such as fire and the first spears.

While we think these are simple tools today innovations such as these gave us the advantage over the various large mammals that early humans lived alongside. As we look back at the history of life on Earth we see that each era brought a new change to our planet that helped life move forward in an amazing variety of ways. From the very beginnings of water and oxygen to the awesome Dinosaur all the way to the modern period that we live in today. With each era producing some grand new changes to our planet one can wonder what will become of Earth in a million years? Only time will tell but by seeing how the Earth has changed over the years we have a good look at where we have been and where we are headed next.

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The History Of Life On Earth. (2022, Feb 27). Retrieved from

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