The History of Life on Earth

Did you know that the planet Earth is more than four-and-a-half billion years old? If you’ve ever been curious about how the world has come to resemble the Earth we know and love today, here is a look at the different eons of Earth’s history that led to the features we recognize and rely upon.

When we think about history, we typically think about relatively recent events, like all of the different milestones achieved by modern humans, as well as all the wars, tragedies, and governments human beings have caused, endured or benefited from. But human history and the history of Earth are extraordinarily different. In fact, human history represents only a tiny fraction of the time the planet Earth has existed!

Modern human history is clearly critical to understand for a variety of reasons. However, the history of planet Earth gives us invaluable information that helps us comprehend numerous other disciplines, including biology, chemistry, environmental sciences, anthropology, genetics, and many more.

The planet is more than four billion years old. To better understand what occurred during the many hundreds of millions of years from Earth’s inception to today, we must learn more or less when certain events occurred. In order to do that, we have to date different specimens as accurately as possible.

The Fossil Record

Examining the age of different rocks offers clues into the environmental conditions of previous eras. Historically, this has, in large part, been done by studying rock formations and deposits that lie deep within the surface of the Earth. The deeper the rock, the older it likely is. This is because newer formations and deposits build on top of the older rocks over time, burying them deep beneath the surface.

However, scientists have developed a more precise method for discovering the age of rock deposits. This achievement gives us the ability to correctly identify the ages of different rocks regardless of where they were found, providing us with better insight into how the Earth evolved over hundreds of millions of years. This technique involves radioactive dating. Radioactive dating is a process that tests the rate of decomposition of materials within the rock sample. When an element breaks down, we can measure the time it takes for the element to degrade to determine how old the formation is. There are several types of radioactive dating, including uranium-lead dating, potassium-agon dating, and radiocarbon dating. These dating technologies help scientists determine the likely age of fossils embedded in rock formations. Assessing the ages of different fossils within rock formations allows us to create an accurate fossil record.

Understanding the fossil record helps us uncover the true history of Earth. Fossils are rare – the overwhelming majority of organisms degrade entirely over time, leaving no trace of their existence, so fossils are precious pieces of the geological record. Analyzing fossils is a vital part of learning about the earliest life on Earth.

Understanding the Earth’s Timeline

When we speak of the history of the Earth, we are talking about the Supereons, eons, eras, and periods that make up the spaces of time between the formation of the planet and today. These are collectively known as the geologic time scale.

Learning the different characteristics of the earliest fossils and rock formations allows us to get a glimpse into the various periods throughout the Earth’s history. Knowing more about the diverse traits of fossils and geological formations gives us the tools to make determinations about climate and biological evolution, and how they shaped what life on Earth was destined to become.

In general, the history of Earth is divided into three separate eons:

  • Archean
  • Proterozoic
  • Phanerozoic

The different eons are marked by the introduction of the elements that are critical to creating and sustaining life and the degrees to which the Earth matured. The very earliest geological eons are part of what is known as the Precambrian supereon.

The Precambrian Supereon

When we talk about the Precambrian supereon, we are referring to the Archean and Proterozoic eons, as well as the Hadean eon. The Precambrian supereon encompasses not only different time periods on Earth, but also the period that pre-dates the formation of the planet. It begins with the Hadean eon, which makes up the beginning of our solar system.

The Hadean eon starts with the formation of our solar system and ends approximately four billion years ago. This period saw the earliest part of Earth’s development when a variety of geological events took place, including the formation of the moon. Scientists speculate that the Earth was violently struck in its very early development, causing a large section of the planet to break away and forming the natural satellite, which is the largest in our solar system relative to the planet it orbits.

During the Hadean eon, the newly formed Earth was incredibly hot and intensely gaseous, and it was this environment that formed the Earth’s atmosphere, which was mainly carbon dioxide. This was the period when the elements that are essential for supporting life were being churned.

The period immediately following the Hadean eon is called the Archean eon. This period lasted from approximately four billion to two-and-a-half billion years ago. During this period, based upon what scientists have been able to determine from microfossils of the period, the surface of the Earth was highly unstable due to aggressive volcanic activity. Huge quantities of the carbon dioxide that filled the newly formed atmosphere were absorbed by limestone deposits in the oceans. This activity triggered the formation of terrestrial islands and weather activity in the atmosphere.

Life began in the oceans during the Archean eon. These were single-celled organisms able to thrive in saltwater and extreme heat, and forms of green algae. The proliferation of these life forms further altered the Earth’s atmosphere, generating oxygen, which supported the proliferation of other organisms. It was the abundance of living organisms that marked the start of the Proterozoic eon, which took place between two-and-a-half billion and 540 million years ago.

This era saw the continuing evolution of single-celled organisms into multicellular organisms. By the end of the Proterozoic era, we find fossil evidence of invertebrates like jellyfish. Moreover, the organisms that were able to exist in nitrogen-rich environments started to die off as oxygen proliferated. The Proterozoic era ended as multi-celled organisms flourished.

The Phanerozoic Eon

There is a higher volume of information from the Phanerozoic era than there is from the previous periods, even though this eon represents a shorter timeframe. This eon lasts approximately 500 million years, and is further subdivided into the following eras:

  • Paleozoic
  • Mesozoic
  • Cenozoic

Additionally, within these eras are separate periods that represent specific environmental traits. The Cambrian period in the Paleozoic era saw a proliferation of highly diverse life forms, most notably the migration of life from the oceans and onto land.

The Cambrian period not only saw the growth of animal life, but a huge increase in plant life also occurred, too, which facilitated further biodiversity. We first see reptiles and insects during this period.

However, the end of the Cambrian period marked the extinction of numerous life forms, though some organisms did transition into subsequent eras.

The next era – the Mesozoic – is noteworthy for being the era of the dinosaurs. While we mainly envision huge stegosauruses or tyrannosauruses when we think of dinosaurs, the sizes of the animals ranged wildly. As far as plant life, the majority are believed to have been non-flowering varieties, which are seen largely during the last era – the Cenozoic.

The dinosaurs had largely gone extinct by the beginning of the Cenozoic era, which is the era we are currently in, although a different, much later, period. The Cenozoic era brought mammals and primates – and human ancestors.

Studying the Earth’s history gives us an ever-evolving understanding of biological phenomena, climate science, evolution, and much more. At Forest Founders, we work to raise awareness of the importance of maintaining healthy global forests and conserving resources, so that the Earth can continue to function and thrive throughout the forthcoming eons. To learn more about how you can participate in reforestation efforts, please visit our information page.