Earth history is a fascinating subject. This 5-part series presents Earth's history in a chronological order with major events and eras explained. Links to the other parts are provided at the bottom of the article.

This text is taken out of my free online program MENTOR EARTH. It contains video material with images that explain all concepts even better. It is free (no hidden costs, no credit card required, no upselling). Read this blog article series or the course website if you want to learn more about it.

____________________________________________________________________________________

Notes

1. Abbreviations used in this text:

• • Ga = gigayears = a billion years

  • Ma = megayears = a million years

  • e.g. 4 Ga means four billions years ago from today.

2. This article explains the geologic time scale.

____________________________________________________________________________________

Part 2: Ediacaran – Silurian 

Neo-Proterozoic Era / Ediacaran Period (635-539 Ma)

575 Ma

Fossils of up to 80 cm or 35 inches tall, complex, soft-bodied organisms without hard shells or internal skeletons appear. Not their actual bodies are preserved today, but their body’s imprints in soft sediments. They lived on continental shelfs in the sea and their imprints were first discovered in the Ediacaran Hills in Australia, which is why this Period at the end of the Proterozoic Eon is called the Ediacaran Period, and this assemblage of fossils was labeled Ediacaran Fauna. The Ediacaran Fauna is important because it contains unprecedented evidence of the first larger organisms and, even more importantly, multicellular organisms, so organisms that consists of more than one cell.

555 Ma

Another fossil assemblage of particular importance has a very cute name: Small Shelly Fauna. This fauna contains tiny, millimeter-sized fossils that were, for the first time, composed of calcium carbonate, calcium phosphate or silica, which is silicate dioxide. These mineralized hard shells appear for the first time about 555 Ma ago, but are especially present during the Early Cambrian, and these tiny fossils were produced by organisms. Biomineralization, the process in which organisms produce minerals and mineralized body parts and is an unprecedented biological innovation at this time. Again, not the actual organisms, their bodies, are preserved today, but their skeletons, the shells or tubes they built. Your body produces biominerals, too: for example your bones and teeth.

600 Ma

The transient supercontinent Pannotia assembled and is located around the South Pole, but it only exists for about 50 Ma. It breaks up to form the continents of Laurentia (North America and Greenland), Baltica (North- and East Europe including Norway, Sweden, Finland, the Baltic States, Ukraine, Belarus, Western Russia), Siberia (Siberia) and Gondwana. Gondwana is the largest continent at the time, stretches from the South Pole to the equator and will be mostly stable for the next 290-370 Ma years. Gondwana comprises the continents Antarctica, Australia, Africa, South America, Madagascar, Arabia, and India.

We’re now leaving the Proterozoic Eon behind. With almost 2 billion years the Proterozoic Eon is the longest time interval in Earth’s history. We’re entering the Phanerozoic Eon, the Eon that we’re currently in.  

Paleozoic Era / Cambrian Period (539-485 Ma)

During the Cambrian, the evolution of animal life picks up the pace and biodiversity increases drastically in an event oftentimes called the “Cambrian Explosion”. The Cambrian Explosion lasted for about 30-40 Ma. Trilobites roam the ocean floors and dominate the Cambrian Period from about 520 Ma to 485 Ma. Most likely, there are no land animals or plants yet.

In the Cambrian, the continents Laurentia, Baltica, Siberia and Gondwana. They are located south of the equator, on the equator and only a few degrees north of the equator. The vast Earth-spanning super ocean is called Panthalassa or Panthalassic Ocean, it opened up when the supercontinent Rodinia fell apart. The ocean between Baltica and Gondwana is called Tornquist-Ocean and the ocean between Laurentia and Baltica is called Iapetus Ocean.

Paleozoic Era / Ordovician Period (485-444 Ma)

The three continents Laurentia, Baltica and Siberia approach each other, and at the north rim of Gondwana, a small continent, a microcontinent, called Avalonia that consisted of several terranes, splits off and drifts northward. It contains the continental cores of South Ireland, England, and Northern Germany. The northward motion of Avalonia opens up the Rheic Ocean between Avalonia and Gondwana. Sea levels were about 200 m higher than today.

In the Ordovician, marine life experiences yet another increase in biodiversity. This diversification of animal life in the Ordovician Period is called the Great Ordovician Biodiversification Event (GOBE). The oldest spores found indicate that during the Ordovician the first plants have invaded the land at least in the Ordovician, most likely even in the mid-Cambrian, as a study finds. At the same time, the first fish without jaws appear in the oceans and, for the first time, corals that build coral reef structures are present in the oceans as well.

At the end of the Ordovician and the beginning of the Silurian Period about 85 % of all marine species become extinct during the Late Ordovician Mass Extinction (LOME), the second most important extinction event in the Phanerozoic Eon, so in the past 540 Ma. It’s believed that this mass extinction was caused by a short but intense global cooling event with glaciers on the continents, especially on Gondwana, and, consequently, reduced sea levels. Other contributing factors have to be taken into account and are investigated as well. This is the second-most severe mass extinction in Earth’s history. A mass extinction is an event during which biodiversity decreases drastically globally across all ecosystems which in other words means many, many species die. All this happens in a geologically speaking short time frame. Even though the sentence “85 % of marine species died” is said in a matter of seconds, mass extinctions are not completed as quickly. They’re not literally sudden events that happen in seconds or even minutes, but that take hundreds of thousands or millions of years.

In geology, the words “quick” or “rapid” in a geological context can describe different duration. When I speak of a rapid decline in biodiversity, I mean it took thousands or millions of years. Only in hindsight, relative to the rest of Earth’s timeline, are these events rapid and the decrease of organisms becomes visible. In contrast, Earthquakes are extremely sudden events that last mere seconds, and the effects are visible instantly. The moral of the story: Time is relative.

Paleozoic Era / Silurian Period (444-419 Ma)

After the mass extinction, the Silurian Period starts. The most important paleobiological event during the Silurian is the continued invasion of plants and animals on land. Spiders, scorpions, and millipedes are the first animals to make landfall. The first plants on land are very primitive with very weak vascular systems, as they have to get used to living in air rather than in water.

At the same time, the continents of Baltica, Laurentia and Avalonia collide, subducting the ancient Iapetus and Tornquist Oceans. The result of this continental collision is the formation of the Caledonian Mountains in northern Europe and the northern Appalachian Mountains in northeastern America. The Caledonian Mountains is an equator-straddling massive mountain chain similar in size to the modern Alps or even Himalayas. The Caledonian Mountains connect the ancient continents of Laurentia, Avalonia and Baltica, now jointly called Laurussia, Old Red Continent or Euramerica. Today, remains of the Caledonian Mountains can be found on the eastern coast of North America and the Appalachian Mountains, in Scotland, Ireland, Norway, and Greenland. The closure of the Iapetus and Tornquist Oceans and the formation of Laurussia preceded the formation of the supercontinent Pangea.

The vertical sediments, the 430-million-year-old greywackes, from the basement layer at Siccar Point (Hutton's Unconformity), were deposited in the Iapetus Ocean and compressed and folded into schists when the continents of Baltica, Avalonia and Laurentia collided during the so-called Caledonian Orogeny that formed the Caledonian Mountains. An orogeny is a process where mountains are formed.

____________________________________________________________________________________

This was Part 2: Ediacaran to Silurian

You find the other parts here:

Part 1: Hadean to Proterozoic

Part 3: Devonian to Permian (comes soon)

Part 4: Triassic to Cretaceous (comes soon)

Part 5: Paleogene to Holocene (comes soon)

____________________________________________________________________________________

This 5-part series is about Earth’s history and the key events that happened since the formation of Earth using a chronological timeline. The knowledge about the past has the power to increase our gratitude and appreciation for what we currently have in our lives. These emotions go beyond the profound appreciation for the planet and permeate all areas of our lives. Pondering the future causes us to be aware that the world keeps on spinning after we’re gone. Then, there emerges a sense of responsibility to take care of the planet for future life. The simple awareness of the fact that Earth has a past and a future, that it existed before us and will exist long after our own individual death, causes a shift in our perception. Suddenly, we’re not owning the planet, but we inhabit it briefly. This awareness of time and our place on this planet can positively influence our behavior and attitude towards all forms of life, and turn us into thoughtful decision-makers, as our innate appreciation for nature is activated.

Yours,

Daniela

____________________________________________________________________________________

Sources

Images

Headline image: Modern shells at Loutra Oreas Elenis, Ελλάδα, photographed by George Girnas and downloaded at Unsplash

Text

Please find all the sources listed in a spreadsheet that is available for download in my program MENTOR EARTH