If we are going to learn about the Earth, we had better start from the beginning! The Hadean, Archean, and Proterozoic eons will take us all the way from the formation of the Earth, 4.6 billion years ago, until about half a billion years ago, so it's a very nice chunk of time. A lot happened over that time, in the way of the changing conditions on the Earth and its topography, as well as the emergence and evolution of life. There is so much to discuss, so let's dive right in!
Script by Jared Matteucci
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If we are going to learn about the Earth.
The best way to do it is to start the story from the beginning.
We want to know about the history of the Earth, from its formation until present day, so that we have the proper context as we learn about all kinds of geological structures throughout this series.
As for the origin of the solar system and planetary formation in general, that is covered over in the astronomy series.
So we won’t review that information.
Instead, let’s just start at the precise time period that Earth first formed, which, by our best estimates, is around 4.57 billion years ago.
Do we get from then to now? First, some terminology.
In order to understand the timescales that Earth operates.
On, geologists came up with a way to break down the 4.57 billion years of Earth’s existence into smaller chunks called eons.
There are four eons.
These are the Hadean, Archean, Proterozoic, and Phanerozoic.
In, the earliest days of Earth’s history, from 4.54 billion to about 4 billion years, ago, Earth would have been unrecognizable to us.
It was a hostile place with no continents, ubiquitous, active volcanism, and frequent asteroid.
Given this description.
It seems appropriate that this eon, the Hadean, is derived from the Greek word, Hades, meaning the underworld, which is a fitting comparison to this hellish landscape.
The frequent asteroid impacts were a result of the solar system being so very young, with huge numbers of large rocky bodies that had not yet been incorporated into planets or ejected from the system.
A particularly notable event is believed to have occurred.
4.4 billion years ago, when a Mars-sized protoplanet named Theia slammed into Earth, creating a worldwide magma ocean, and producing the tilt in Earth’s rotational axis in the process.
Though Earth and Theia, mostly coalesced.
The impact caused parts of the crust and mantle of both planets to be ejected into space, generating a ring of debris which collected to form our Moon.
The moon is partly made of the Earth.
The collision, Earth began a slow journey toward more calm conditions, as proto-continents and oceans began to form.
However, conditions were still extremely harsh due to constant asteroid bombardment, which would continue until around 3.8 billion years, ago.
This likely hindered any development of life during this time.
No rocks of Hadean age exist in the rock record, simply because older rocks are more likely to be destroyed or altered by geologic processes.
Only surviving terrestrial material from this time are zircon crystals, which are durable and can survive.
Processes like subduction and weathering.
This makes the Hadean eon the most mysterious time in Earth’s history.
The next eon, the Archean, lasted from 4 billion to 2.5 billion years.
One of the most important events in the Archean was the tapering-off of heavy asteroid bombardment and the subsequent emergence of life.
The oldest terrestrial rocks, as well as fossils, come from this eon.
The oldest fossils are 3.48-billion-year-old stromatolites, which are the rocky remnants of microbial mats formed by cyanobacteria living in tidal flats.
Abundance of these fossils suggests that by the Archean, single-celled life was already flourishing on Earth.
Another main event of the Archean was the formation of large continents.
Remnants of these ancient continents are called cratons and are found mainly in Canada, Africa, and Australia.
The cratons formed via accretion of many smaller microcontinents as they collided along ancient subduction.
This is essentially the same process that caused India to collide with Asia, to form the Himalayas, just on a much larger scale, and which will eventually cause North America to collide with Asia, hundreds of millions of years in the future.
This is a good time to mention that Earth’s, crust, or outer layer, is broken into rigid chunks and pushed around by the convection of the layer beneath it.
The mantle, which, even though it is made of solid rock, can flow like a viscous liquid.
Under the intense pressures and temperatures found deep within the Earth.
We will talk more about continental drift and plate tectonics later in the series.
By, the end of the Archean, Earth looked more or less like it does today, having oceans and large continents with rivers and lakes, but in other ways it was still very different from the Earth we know.
The Earth’s atmosphere, for instance, had 100,000 times less oxygen than the air we’re breathing right now, instead containing large amounts of carbon dioxide and methane.
Life, was also exclusively unicellular and would continue to be so for at least an additional billion years.
The next eon, the Proterozoic, lasted from 2.5 billion years ago to 541 million years ago, and began with a gradual increase in atmospheric oxygen, which was generated by newly evolved cyanobacteria with photosynthetic capabilities.
This oxygen was absorbed by the oceans at first, which acted as a buffer, preventing a rapid increase in atmospheric oxygen, but the oceans eventually became saturated with oxygen, allowing atmospheric oxygen levels to rapidly soar, increasing by a factor of 100., Banded, Iron, Formations, or BIFs, are marine deposits from this period and are characterized by thick deposits of iron oxides, which precipitated from ocean water as oxygen concentrations.
BIFs were not formed during any other period of Earth’s history.
The rapid increase in oxygen in both the atmosphere and oceans caused a mass extinction of obligate anaerobes, which are organisms that are poisoned by oxygen.
This event is called The, Great, Oxidation Event, or perhaps from the perspective of the anaerobic organisms that abruptly died, the Great Oxygen Catastrophe.
The skies and oceans shifted from orange and green-tinted to the blue.
We see today.
The evolution of unicellular eukaryotes occurred during the Proterozoic.
We learned in the biology series.
These are single-celled organisms containing nuclei and other highly specialized organelles like mitochondria and chloroplasts, through a process called endosymbiosis, where certain prokaryotic organisms were incorporated into others, with organelles like mitochondria and chloroplasts, being derived from the “eaten” prokaryotes, so to speak., The, first multicellular, life, and even animals, also evolved during the Proterozoic.
The oldest indisputable animal fossils are from 570 million years ago and are called the Ediacara Fauna.
Examples of these primordial fauna are Charnia, a frond-like animal, Spriggina, a worm-like animal, and Kimberella, a mollusk-like, animal.
Large diversity of animal fossils present in these rocks indicates that animals were rapidly evolving as nature experimented with different body.
The Proterozoic was also a time of supercontinents.
Converging continents collided around 1.8 billion years ago to form the first supercontinent, called Nuna.
However, around 1.5 billion years.
Ago, convection currents in the mantle changed direction, causing Nuna to break apart, or rift.
The assembly and later break-up of supercontinents is a cycle that was to repeat an additional two times in Earth’s history.
With another cycle occurring later in the Proterozoic, with the formation and breakup of Rodinia between 1.1 billion and 750 million years, ago.
During rifting, a large chunk of Rodinia called Pannotia, broke off and moved over the south pole, which greatly affected Earth’s climate, triggering a massive ice age.
As glaciers formed over the south pole and expanded northward.
The glaciation peaked 100 million years later in a “Snowball Earth”, where most of the planet’s surface was covered with ice.
Average global temperatures dropped to negative fifty degrees Celsius, only about 10 degrees warmer than the average temperature of modern-day Antarctica.
First, three eons we just discussed, the Hadean, Archean, and Proterozoic, are commonly grouped into one super, eon called the Precambrian.
The end of the Precambrian, which was 541 million years.
Ago, was marked by an incredible diversification of life called the Cambrian explosion.
This explosive event was a continuation and acceleration of the rapid evolution that was occurring during the Neoproterozoic.
Every major animal phylum that we know of today, and are learning about in the zoology series, can be traced back to these early, intricate life, forms.
Bright, green algae, flourished, armored arthropods, like trilobites roamed, the ocean floors and jawless fish resembling giant, shiny worms swam through the water.
Then, the Phanerozoic eon, began.
This is the eon.
We are still living in today, let’s move forward and take a closer look at this next.
The Hadean Eon, named after the Greek god and ruler of the underworld Hades, is the oldest eon and dates from 4.5–4.0 billion years ago. This time represents Earth's earliest history, during which the planet was characterized by a partially molten surface, volcanism, and asteroid impacts.What major events in Earth history occurred in the Hadean eon? ›
The Hadean Eon is characterized by Earth's initial formation—from the accretion of dust and gases and the frequent collisions of larger planetesimals—and by the stabilization of its core and crust and the development of its atmosphere and oceans.What is the Hadean and Archean eons? ›
The Archean Eon was preceded by the Hadean Eon, an informal division of geologic time spanning from about 4.6 billion to 4 billion years ago and characterized by Earth's initial formation. Records of Earth's primitive atmosphere and oceans emerge in the earliest Archean (Eoarchean Era).What is the history of the Earth Archean? ›
Thus, the Archean Eon is a geologic eon, 4000–2500 million years ago (4–2.5 billion years ago), that followed the Hadean Eon and preceded the Proterozoic Eon. During the Archean eon, the Earth's crust cooled enough that rocks and continental plates began to form.When did life first appear on Earth? ›
The earliest life forms we know of were microscopic organisms (microbes) that left signals of their presence in rocks about 3.7 billion years old.What was the first period on Earth? ›
The earliest time of the Earth is called the Hadean and refers to a period of time for which we have no rock record, and the Archean followed, which corresponds to the ages of the oldest known rocks on earth. These, with the Proterozoic Eon are called the Precambrian Eon.What major events happened in the Archean era? ›
During the Archean Eon, methane droplets in the air shrouded the young Earth in a global haze. There was no oxygen gas on Earth. Oxygen was only in compounds such as water. Complex chemical reactions in the young oceans transformed carbon-containing molecules into simple, living cells that did not need oxygen to live.What are the three major eons of Earth's history from the oldest to the most recent? ›
The eon is the broadest category of geological time. Earth's history is characterized by four eons; in order from oldest to youngest, these are the Hadeon, Archean, Proterozoic, and Phanerozoic.What are the 4 eons? ›
For example, the entire age of the earth is divided into four eons: the Hadean Eon, the Archean Eon, the Proterozoic Eon, and the Phanerozoic Eon. These four eons are further subdivided into eras (Table 7.3). Fig.What is the difference between Hadean eon and Archean eon? ›
This eon represents the beginning of the rock record. Although there is current evidence that rocks and minerals existed during the Hadean Eon, the Archean has a much more robust rock and fossil record.
Precambrian (Informal—4.6 billion years ago to 541 million years ago) Precambrian is the informal name for the first 4 billion years, or 88 percent, of Earth's history. It includes the Proterozoic and Archeon Eons.What are the three eons of Earth's history? ›
Three eons are recognized: the Phanerozoic Eon (dating from the present back to the beginning of the Cambrian Period), the Proterozoic Eon, and the Archean Eon. Less formally, eon often refers to a span of one billion years.How old is the Earth in years? ›
Today, we know from radiometric dating that Earth is about 4.5 billion years old. Had naturalists in the 1700s and 1800s known Earth's true age, early ideas about evolution might have been taken more seriously.Who were the first humans on Earth? ›
The First Humans
One of the earliest known humans is Homo habilis, or “handy man,” who lived about 2.4 million to 1.4 million years ago in Eastern and Southern Africa.
In fact, we may distinguish five theories that Darwin combined: evolution as such, common descent, gradualism, multiplication of species, and natural selection.How did human life start on Earth? ›
Scientific evidence shows that the physical and behavioral traits shared by all people originated from apelike ancestors and evolved over a period of approximately six million years. One of the earliest defining human traits, bipedalism -- the ability to walk on two legs -- evolved over 4 million years ago.In what order did life appear on Earth? ›
Plants and fungi did not appear until roughly 500 million years ago. They were soon followed by arthropods (insects and spiders). Next came the amphibians about 300 million years ago, followed by mammals around 200 million years ago and birds around 150 million years ago.What era do we live in now? ›
The Anthropocene Epoch is an unofficial unit of geologic time, used to describe the most recent period in Earth's history when human activity started to have a significant impact on the planet's climate and ecosystems.What is the real history of the Earth? ›
Earth formed as part of the birth of the solar system: what eventually became the solar system initially existed as a large, rotating cloud of dust and gas. It was composed of hydrogen and helium produced in the Big Bang, as well as heavier elements produced by stars long gone.What are 3 major events that took place during Precambrian time? ›
The Precambrian was the "Age of Early Life." During the Precambrian, continents formed and our modern atmosphere developed, while early life evolved and flourished. Soft-bodied creatures like worms and jellyfish lived in the world's oceans, but the land remained barren.
The Precambrian ended with a mass extinction, which paved the way for the Cambrian explosion.What are 3 interesting facts about the Precambrian era? ›
Precambrian Facts & Information: The Birth Of A Planet And The First Life On Earth. The Precambrian began with the birth of Earth and saw the formation of the moon, the creation and breaking up of supercontinents, the first oceans, the introduction of oxygen into the atmosphere, and the appearance of life on Earth.What life forms lived during the Archean eon? ›
Life in the Archean was limited to simple single-celled organisms (lacking nuclei), called prokaryotes. In addition to the domain Bacteria, microfossils of the domain Archaea have also been identified.What was Earth's climate during the Hadean eon? ›
(1) The Hadean climate after the early warm greenhouse ceased was clement or icy. Life originated and colonized the planet, some species adapting to thermophile lifestyles at hydrothermal events and in the kilometer-deep surface. A large asteroid impact boiled much of the ocean leaving only thermophile survivors.What did the Earth's earliest atmosphere in the Hadean and Archean eons contained abundant? ›
Earth in the early Hadean had a very thick carbon dioxide atmosphere, but eventually oceans of liquid water formed.What are the 4 major eras in Earth's geologic history which one lasted the longest? ›
The four main ERAS are, from oldest to youngest: PreCambrian, Palaeozoic, Mesozoic and Cenozoic. Periods are a finer subdivision in the geological time scale.What are the four biggest eras in geologic history? ›
From these stories, scientists have divided geologic history into four major parts. These divisions are Precambrian time, the Paleozoic era, the Mesozoic era, and the Cenozoic era.What are the three eras that make up Earth's history and would be the most important for the introduction of the first mammals? ›
The three eras that make up Earth history are: Paleozoic, Mesozoic, and Cenozoic.How many years is a era? ›
One Era is hundreds of millions of years in duration. Period: This is the basic unit of geologic time. A Period lasts tens of millions of years, which is the time it takes to form one type of rock system.Is an eon longer than an era? ›
Vocabulary: eon = The largest unit of time. era = A unit of time shorter than an eon but longer than a period.
An eon can be referred to as indefinite duration or extremely long period of time. Eons is said to have the longest duration because it is more than one era or a period or an epoch.Did life exist during the Hadean eon? ›
It is unlikely that life could have formed and established in the extremely volatile conditions of the Hadean Eon. If life had begun to form at this time, it most likely would have been destroyed over and over again until optimum conditions were in place for life to take a foothold.Did life exist in the Archean eon? ›
It was early in the Archean that life first appeared on Earth. Our oldest fossils date to roughly 3.5 billion years ago, and consist of bacteria microfossils. In fact, all life during the more than one billion years of the Archean was bacterial.During which eon did Pangaea come together? ›
At the beginning of the age of dinosaurs (during the Triassic Period, about 230 million years ago), the continents were arranged together as a single supercontinent called Pangea.How many eras are there in Earth's history? ›
Ten eras are recognized by the International Union of Geological Sciences: the Eoarchean Era (4.0 billion to 3.6 billion years ago), the Paleoarchean Era (3.6 billion to 3.2 billion years ago), the Mesoarchean Era (3.2 billion to 2.8 billion years ago), the Neoarchean Era (2.8 billion to 2.5 billion years ago), the ...What is the correct order of the geological time scale of the earth? ›
The correct order is Cenozoic- Mesozoic-Palaeozoic-Precambrian.How many ages ago is an eon? ›
Eon goes back to the Greek aiōn, "age." An age is not easy to measure, and neither is an eon. Both are just really long periods of time, but in science an eon is about a billion years.What ended the Hadean eon? › What are the facts about eon? ›
In formal usage, eons are the longest portions of geologic time (eras are the second-longest). Three eons are recognized: the Phanerozoic Eon (dating from the present back to the beginning of the Cambrian Period), the Proterozoic Eon, and the Archean Eon. Less formally, eon often refers to a span of one billion years.How hot was Earth during the Hadean eon? ›
The heat flow from the Earth's interior was ∼140 W/m2. The surface remained hot 1800–2000 K, partially molten with some solid scum.
Answer and Explanation: Scientists study the Hadean Eon by studying rocks from that time. The Hadean is an early part of the earth's history that lasted from 4.6 to 4 billion years ago.What eon are we currently in? ›
The Phanerozoic Eon is the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years ago to the present, and it began with the Cambrian Period, when animals first developed hard shells preserved in the fossil record.How many years is era? ›
Two or more periods compose on Era. One Era is hundreds of millions of years in duration. Period: This is the basic unit of geologic time.How many years is 1 eon? ›
An eon is a period of time equal to one billion years or 1,000,000,000 years. The word is of Greek origin and approximately translates to "age."How many years is eons? ›
Eon goes back to the Greek aiōn, "age." An age is not easy to measure, and neither is an eon. Both are just really long periods of time, but in science an eon is about a billion years.What caused Earth to cool down? ›
Past studies have shown that the cooling trend is driven by greenhouse gases, as well as shifts in the Earth's magnetic field and the roughly 11-year cycle in the sun's solar activity.Was the Earth hot at first? ›
Our 4.54-billion-year-old planet probably experienced its hottest temperatures in its earliest days, when it was still colliding with other rocky debris (planetesimals) careening around the solar system.When did Earth have liquid water? ›
Research funded partly by NASA has confirmed the existence of liquid water on the Earth's surface more than 4 billion years ago. Scientists have found that the Earth had formed patterns of crust formation, erosion and sediment recycling as early as 4.35 billion years ago.What is the evidence of Earth's early history? ›
Fossils that have an estimated age of 3.5 billion years have been found on all of the continents of the earth. Fossils determine many different factors of the rocks and region they are found. The law of fossil succession states, "The kinds of animals and plants found as fossils change through time.