4.6 billion years ago our planet Earth was a geologically tumultuous ball of volcanic rock getting constantly pounded by meterorites. Eventually it’s crust cooled and oceans formed with small islands. The earliest forms of life appeared and eventually continents, much different than those of today, formed into steamy ball of jungle crawling with giant reptiles that today we call dinosaurs. All other forms of life evolved as well bringing us up to modern times.
In this post we’ll explore some of the natural history of our home planet, and who and what lived here before us. Before we go on we should make a distinction between two definitions of the word history. In many cases, history means recorded history, such as when you take a course on European History. Here we study everything we know according to what has been written, or perhaps contained in other media like paintings, records, and videos. It may include some stories that have been passed on by oral tradition as well. But another term for history is simply anything that happened in the past. The great majority of this is unknowable to mere mortals.
When we study natural history, because it is so very long a timeline, we don’t have much recorded and must rely on what forwe can glean from scientific analysis of things like fossils. This requires a fair amount of imagination coupled with a lot of training and scientific knowledge. People have been studying natural history for thousands of years. Pliny the Elder instance, was a Roman naval commander who wrote an 10 volume work entitled Natural History (Historae Naturalis) which was divided into 37 books. Professional scientists today often write in peer reviewed journals as a way of keeping some checks and balances involved in a field that has a fair bit of guesswork involved. Nevertheless, over the years we have gathered lots of data and come to some fairly concrete conclusions about what exactly happened on earth, and when it happened. Let’s dive in.
Here is a great interactive timeline of the history of the universe in terms of geology and evolution:
Using the above timeline and others as sources we can simplify the natural history of earth into different sections of times geologically. This makes it easy to reference any event in the larger picture of earth’s natural history. Beware, different sources may use slightly different names, or even swap them (e.g. where some say period, others may say epoch or era). But here we will organize them according to:
Eons (really long times):
Hadean, Archaeaic, Proterozoic, Phanerozoic
Periods (very long times, less than Eons):
Eoarchaean, Paleoarchaean, Mesoarchaen, Neoarchaean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic, Cenozoic
Eras (still long, but less than Periods):
Siderian, Rhyacian, Orosirian, Statherian, Calymmian, Ecstasian, Stenian, Tonian, Cryogenian, Ediacaran, Cambrian, Ordovician, Silurian, Devonian, Carboniferous (Mississippian and Pennsylvanian), Permian, Triassic, Jurassic, Cretaceous, Tertiary, Quaternary
Epochs (pretty long, but shorter than Periods):
Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene
You can see a table of most of these timespans here: https://en.wikipedia.org/wiki/Geological_period
Now bear in mind, these four designations overlap. That means that the periods are embedded within the eons, the eras are embedded within the the periods, and the epochs are embedded in the eras.
The Hadeon Eon
(4.53 b – 4 b B.C.)
Nearly 4.6 Billion years ago, it seems that there were… rocks on earth in the so called Hadean eon. We know this from a mineral called Zircon which can transform into Uranium over time. We can measure how much of the Zircon has become Uranium to tell the age of the rock. During this eon there was no known life on earth, and it was a tumultous geologic time period with much volcanic activity and frequent meteorite impacts. Later shallow oceans formed with small islands amongst them.
Here is an article about some of the world’s oldest rock specimens:
The Hadeon Eon has no other sections of time embedded in it. Not much is known about it due to the lack of geological evidence, other than a handful of Zircons, left behind. The highlights of this time would be the cooling of the magma into the earth’s crust and it is also believed that the moon was formed when another proto-planet named Theia crashed into the earth.
The Archaeaon Eon
By the time the Archaeaon Eon begins, Earth already had oceans and some primitive landforms. This eon can be divided into four parts:
The Eoarchaean Era 4 b – 3.6 b B.C.
After the earth’s crust formed, the abiotic conditions were present that gave forth the very earliest forms of primitive life. Prokaryotes like cyanobacteriaarose.
The Paleoarchaean Era 3.6 b – 3.2 b B.C.
The next era in the Archaean Eon is the Palearchaen Era, which is an era that is not defined by geological milestones but chronometrically. In this era, microbial mats have been identified as the first ascertained forms of life because they have been found in fossilized form in Australia. The first supercontinent, named Vaalbara was formed during this time by the Kaapvaal Craton which is now located in South Africa, and the Pilbara Craton, which is now found in Western Australia. Vaalbara was named by E.S. Cheney who took the last four letters of both cratons, which are large stable blocks of the earth’s crust that form the nucleus of continents, to form the name. Also of mention is that during this era, an impact event has been detected indicating that a giant asteroid around 37 – 58 km wide collided with earth in what is today South Africa (The Barberton Greenstone Belt), although any signs of a crater have yet to be discovered.
The Mesoarchaen Era 3.2 b – 2.8 b B.C.
During this era cyanobacteria formed layered mounds called stromatolites, of which fossilized forms have been found in Australia indicating they existed during this time. You can read an article about various stromatolites here:
The Pongola glaciation also occurred during this time, as did the breakup of the supercontinent Vaalbara.
The Neoarchaean Era 2.8 b – 2.5 b B.C.
During this time photosynthesis developed. Because this gave off oxygen as part of its biological process, it set the table to “flip” the atmospheric conditions to be rich in dioxygen (O2), leading the way for eukaryotes to arise and the Great Oxygenation Event which led to the near extinction of anaerobic lifeforms during later eras.
The Proterozoic Eon 2.5 b – 544 million B.C.
The Proterozoic Eon is divided into three eras:
The Paleoproterozoic Era 2.5 b – 1.6 billion B.C.
The Siderian Period 2.5 b to 2.3 b B.C.
One of the byproducts of anaerobic life (life which does not require Oxygen to live), is Oxygen. That means, it doesn’t require Oxygen on the intake, but puts it out as a waste product. At this time BIFs, or Banded Iron Formations were formed due to Oxygen reacting with Iron. This cleaned the green out of the oceans and oxygenated the atmostphere.
The Rhyacian Period 2.3 b to 2.05 b B.C.
This time period hosted the oldest and longest ice age on earth, the Huronian Ice Age, which followed the Great Oxygenation Event. This event occurred in the area today called Lake Huron, one of the 5 Great Lakes in North America.
Want to check out an old scholarly journal article written in 1908 about the Huronian Glaciation, check it out here:
The Orosorian Period 2.05 b – 1.8 b B.C.
This period is named after one of its most prominent distinctions, the arisal of orogeny, or in more common terms, the making of mountains due to shifts in tectonic plates. There were also two more very large asteroid impact events during this period.
The Stratherian Period 1.8 b – 1.6 b B.C.
This period marks the end of the Paleoproterozoic Era where cratonization or stabilizing of the earth’s crust occured. Another supercontinent named Columbia (or Nuna, or Hudsonland) was proposed to have existed.
The Mesoproterozoic Era 1.6 b – 1 b B.C.
The Mesoproterozoic Era is divided into three eras:
The Calymnian Period 1.6 b – 1.4 b B.C.
During this time platform covers built upon cratonized areas were expanded and the supercontinent Columbia broke up.
The Ecstasian Period 1.4 b – 1.2 b B.C.
The expansion of platform covers expanded during this era. The Hunting Formation, which exists on Canada’s Somerset Island dates to this period and microfossils of sexually reproducing eukaryotes, the first of their kind, have been found there.
The Stenian Period 1.2 b – 1 b B.C.
This period was characterized by polymetamorphic belts such as those seen here in this Quartzite specimen:
The Rodinia a supercontinent formerly entitled Pangaea, was formed during this period.
The Neoproterozoic Era 1 m – 543 million B.C.
This eon is divided into three periods:
In this period, acritarchs, ancient organic microfossils from these times, show great diversification and around 800 m B.C. the first metozoans, which were the earliest forms of animals, appeared. An example of one of these is Otavia antiqua of which the oldest fossil was found in Namibia.
The Cryogenian Period 720 m – 635 m B.C.
Temperatures plunged during this period, which is best known for the Sturtian and Marinoan glaciations. There is much controversy over whether or not these glaciations covered the entire earth “snowball earth”, or not.
The Ediacarian Period 635 m – 543 m B.C.
During this period, multicellular fossils emerge in the fossil record including creatures such as worms and fronds. The moon was closer to earth at this time then it is now causing more intense tidal activity.
The Phanerozoic Eon 542 million B.C. – Present
The Phanerozoic Eon can be divided into three eras:
The Paleozoic Era 541 m – 252 m B.C.
Cambrian Period 541 m – 485.4 m B.C.
The Cambrian Explosion saw a great diversification of metazoa that all seeming evolved from one previous ancestor although all of the lifeforms were nearly all oceanic at this time as there was little floraon land to support fauna. It was previously thought that trilobytes were the dominant form of life during this period but now it is known that arthropods were dominant, and the trilobytes just fossilized better due to their calcium carbonate (CaCO3) armor.
Ordovician Period 485.4 m – 443.8 m B.C.
This period saw both great extinction of the above mentioned trilobytes as well as other creatures like brachiopods and graptolites. This mass extinction was may well have been induced by climate change caused by glaciations pushing cooler temperatures although there are other theories as well. The fossils produced by this extinction would later become the core supply of “fossil fuels” like petroleum. At the same time the Great Ordovician Biodiversity Eventsaw more complex animal life evolve, and fish with jaws began to appear during this time.
Silurian Period 443.8 m – 419.2 m B.C.
This period saw the diversification of jawed and bony fish as well as the spread of flora and arthropods to terrestrial habitats. The extinction event that had begun in the Ordovician Period continued and ended during this period.
Devonian Period 419.2 m – 358.9 m B.C.
This period has been dubbed the “Age of Fishes” as well as the “Old Red Age” due to the sandstone deposits in England where many fossils from this period were found. Forests emerged on continents during this period, the dominating of which was Gondwana which was accompanied by Euramerica. There was much tectonic activity during this time which was characterized by warmer temperatures and no glaciers. There was another extinction event during this period as well.
Carboniferous 358.9 m – 298.9 m B.C.
This period derives it’s name from two Latin roots, carbo and fero which combine to make Carboniferous meaning “coal bearing” and is named such due to the numerous coal deposits discovered that date to this period. In North America, this period is divided into two sections, the Mississippian and the Pennsylvanian. The continents were heavily forested at this time and their remnants would form the aforementioned coal beds. Amphibians were the most prominent land vertabrates and some of them evolved into the world’s first vertabrates that lived only on land. Plantlife such as ferns, mosses and scrambling plants were common at this time. At the end of this period was the Carboniferous Rainforest Collapse.
Permian Period 298.9m – 259.902 m B.C.
This period saw the rise of amniotes into mammals and reptiles, which were able to better adapt to the deserts created by the rainforest collapse in the previous period than amphibians. At this time there were two main continents, Pangaea and Siberia surrounded by a global ocean called Panthalassa. This period ended in the greatest extinction event in the history of earth, the Permian-Triassic Extinction Event of which numerous causes have been suggested ranging from an impact event, to volcanism to anoxic conditions and many more. 83% of all genera were wiped out and It would take ecosystems on land 30 million years to recover, going deep into the following Triassic Period.
The Mesozoic Era 252 m – 66 m B.C.
The Mesozoic Era can be divided into 3 periods:
Triassic Period 251.9 m – 201.3 B.C
This period saw complex animal life arise in the form of Therapsids, early mammals whose legs protruded vertically down from their bodies unlike reptiles, and Archosaurs, of whom birds and crocodiles can both claim as ancestors. Later, a subset of the Archosaurs called Dinosaurs would live during this period. The climate of the times was hot and dry and deserts sprawled across much of Pangaea. The end of the period would see yet another major extinction event, the Triassic-Jurassic Extinction Event which allowed the dinosaurs to gain dominance in the following period.
Jurassic Period 201.3 m – 145 m B.C.
Known as the “Age of Reptiles”, this period was rife with scaly, shelled, horned and winged giant creatures, of whom the fossils make astounding discoveries in the field of archaeology. This age is famed for massive terrestrial creatures like Diplodocus which may have even breached 50 meters in length. This age also saw the arrival of birds, examples of which are Archaeopteryxand there was no shortage of forests and flora either, with conifers being the dominant plant life at this time.
Cretaceous Period 145 m – 66 m B.C.
The warmer climate of this period led to rising seas, the the continued diversification of mammals, birds and flowering plants, and continued dominance by dinosaurs such as the the fearsome Tyrannosaurus rex who literally made it to the silver screen inthe blockbuster movie Jurassic Park, even though it lived in the late Cretaceous Period and not during the Jurassic Period. This period ended in a massive extinction event thought to be caused by the impact of a comet or meteor, the crater of which lies in the present day Gulf of Mexico and was discovered in the 1990’s. This theory, for which there is conclusive geological evidence, is known as the Alvarez Hypothesis. This extinction event wiped out 75% of all flora and fauna on earth at the time including all non-avian dinosaurs.
The Cenozoic Era 66 m B.C. – Present
The Cenozoic Era can be divided into 3 periods:
Paleogene Period 66 m – 23.03 m B.C.
This period can be divided into three epochs:
The Paleocene Epoch 66 m – 56 m B.C. saw the origin of placental mammals in warm climates where the continents as we know them today were formed but disconnected by oceans which were now dominated by sharks.
The Eocene Epoch 56 m – 33.9 m B.C. had a temperature of around 30˚C all over earth, and dense forests constrained terrestrial fauna living there to grow to no more than 10kg in weight. Primates, horses, and whales were present during this epoch.
The Oligocene Epoch 33.9 m – 23.03 m B.C. saw the arrival of grass and many species that still survive today such as cats, dogs and marsupials.
Neogene Period 23.03 m – 2.58 m B.C.
This period is divided into two epochs:
Miocene Epoch 23.03 m -5.333 m B.C. saw the further expansion of grass and diversification of apes into 30 species. The Tethys Sea closed leaving the present day Mediterranean, Black, Caspian and Red Seas behind. 95% of modern seed plants evolved during this epoch.
The Pliocene Epoch 5.333 m – 2.58 m B.C. experienced great climatic changes with ice ages that caused the Mediterranean Sea to temporarily dry up. The Isthmus of Panama formed connecting North and South America and allowing fauna to move between them causing great entropy within their habitats. Australopithecas evolved in what is present day Africa during this period.
Quaternary 2.58 m B.C. – Present
The Pleistocene Epoch 2.588 m – 11,700 B.C. is also known as the Ice Age due to it’s numerous glaciations. During this period megafauna such as mastodons and mammoths were present until an extinction event occurred wiping them out along with all neanderthals. Early hominids like Homo erectus lived during this epoch.
The Holocene Epoch 11,700 B.C. – Present saw the progression of hominids towards a neolithic culture that depended less on hunting and gathering and transitioned to agriculture. Then came the rise of major civilizations and modernizations leading to present day life on earth.
Check out Pterosaurs!!!
Some of the sources of this article include:
Coleman, A. P. “The Lower Huronian Ice Age.” The Journal of Geology, vol. 16, no. 2, 1908, pp. 149–158. JSTOR, JSTOR, www.jstor.org/stable/30061916.
Cyanobacteria by MathewJParker CC BY-SA 3.0
Trilobyte fossil by Dwergenpaartje
Dunkleosteus Zachi Evenor from Israelhttps://www.flickr.com/people/40794167@N05
Australopithecas by J.M Salas