Picture source: https://www.geologyin.com/2016/12/10-interesting-facts-about-geological.html

Introduction

Happy World Wildlife Day!

I know that this may be late by a day but I wanted to celebrate a very special post on a very special day- World Wildlife day on the 3rd of march!

So, I'm going to start writing a three-part explained story the History Of Life On Earth.

Each part is going to explain an Era in the Earth's History which had life.

Archean and Proterozoic (Life Before Paleozoic Era)

Life didn't only start in the Paleozoic Era, it started way before, 3.5 billon years ago.

I am going to explain that life in this section and then move to the Paleozoic.

Now, Paleozoic is an era, which is the second-largest unit we use in the geological timeline.

But the largest is eon, which there are 4 of- Hadean (with no life), Archean (where life started), Proterozoic (where life continued), Phanerozoic (where life evolved and diversified).

So, you may have noticed that life started in the Archean.

This is true. The life that started here were microbes, which are unicellular (single-celled) organisms. So they were microscopic in size. They lived in the water.

2.4 billion years ago, cyanobacteria evolved, which was a monumental point in the Earth's history.

These bacteria were the first ever photo-synthesizers, which meant that they got their food from sunlight, carbon dioxide and water, and gave out oxygen as a by-product.

But this oxygen was not present on its own before in mass amounts, but after this event, that exact thing happened.

This made it possible for aerobic respiration (or respiration in the presence of oxygen).

2.1 Billion years ago, multicellular life evolved.

In the Proterozoic Eon, life evolved. Another very important evolution happen, the appearance of the first animals. This happen 800 million years ago (mya). These animals were sponges.

At the end of the Proterozoic eon, an extinction (End Ediacaran Extinction) happen due to climatic changes.

Phanerozoic Eon

Now, I will explain the Eon where life diversified.

Paleozoic Era

The Paleozoic Era is when life on earth became very similar to what we have today.

Cambrian Period

Picture source: https://www.britannica.com/science/Cambrian-Period

A Period is the part in geological timeline under an Era. The Cambrian Period is the first Period of the Paleozoic Era. It lasted for 53.4 million years.During the Cambrian, life diversified.

During the Cambrian, a great diversification of animal lif happen and this was called the Cambrian Explosion which lasted from 541-448 mya (million years ago).

Algae evolved during this time.

The animals became larger with more diverse shapes and adaptations. A new form of protection appeared, hard bodies such as shell and spines.

Burrow digging came along as more and more species used this lifestyle.

The predator and prey relationship also sky-rocketed and became a major part of life.

Picture source : https://www.livescience.com/oldest-cannibalism-found-in-trilobite-fossils

Some animals included Trilobites, Arthropods, etc.

Ordovician Period

The Ordovician Period follows the Cambrian. It spans 41.6 million years.

The life that existed in the Ordovician was also dominated by hard shells and spines.

The Great Ordovician Biodiversification Event was similar to the Cambrian Explosion.

Filter-feeding also boosted in this time and was used much more by organisms than before.

Some organisms included Endoceras, the filter-feeding Aegirocassis, Pentecopterus, etc.

Green Algae was also quite abundant in the Ordovician.

This Period ended with the End Ordovician Mass Extinction.

Endoceras, Picture source : https://commons.wikimedia.org/wiki/File:Endoceras_fulgur.png

Silurian Period

Picture Source : https://en.wikipedia.org/wiki/Silurian

The Silurian Period spanned 24.6 million years.

The Silurian saw a massive leap in evolution as some of the first land plants came along during this time. Moss grew on the banks of rivers and lakes.

This happen in the Silurian to Devonian periods, and so, was called the Silurian-Devonian Land Revolution.

Most of the flora came onto land during the Silurian part of this diversification.

Vascular plants entered the fossil record during the Silurian.

The first bony fish entered in the Silurian.

Some animals included Entelognathus, Eurypterus, Poraspis, Parioscorpio, Pterygotus, Sphooceras, etc.

Entelognathus, Picture source: https://commons.wikimedia.org/wiki/File:Entelognathus.png

Devonian Period

The Devonian Period comes after the Silurian, and it continues the Silurian-Devonian land Revolution. It spanned 60.3 million years.

Though the Silurian part of the Land Revolution was mostly the time when plants became terrestrial, the Devonian part was when the first animals became terrestrial and amphibians evolving.

Tetrapods and Terrestrial Arthropods evolved in the Devonian. Some terrestrial animals included Lobe-Finned fish, Tiktaalik, Acanthostega, Elginerpeton, etc.

Dunkleosteus, Picture source : https://www.mdpi.com/1424-2818/15/3/318

Some marine life included Dunkleosteus, Titanychthys, Onychodus, Coelacanths, etc.

Ferns were common in the Devonian.

This Period ended with The Late Devonian Mass Extinction.

Carboniferous Period

The Carboniferous Period is known as the Age Of Amphibians as amphibians were the dominant species during this time. It spanned 60 million years.

Vegetation in the Carboniferous was similar to that of the Devonian. Scale-Trees and Horse-tails were common plants in the Carboniferous including ferns.

Some animals included amphibians like Microbrachis, and other animals like Pederpes, Hylonomus, Amphibamus, Ornithoprion, Rhizodus, Akmonistion, Dracopristis, Pulmonoscorpius, Megarachne, etc.

Pederpes, Picture source : https://en.wikipedia.org/wiki/Pederpes

Permian Period

The Permian Period is the last Period of the Paleozoic Era. It spans 47 million years.

The Permian saw many larger and different types of Tetrapods. Reptiles and mostly Synapsids were prominent during this time. Synapsids are the ancestors of Mammals.