History of life
Eons:
Eons are large amounts of geologic time and are broken down into eras, periods and epochs
The 4 eons are the hadean, the archean, the proterozoic and the phanerozoic
The hadean is the oldest eon
It starts at the formation of the planet and ends at 4.03 bya, the age of the oldest known intact rock formation
It covers the time of the young Earth
The archean started at 4.03 bya and ended at 2.5 bya
The earliest known life started in the archean
During the archean, the Earth was mostly a water world
The archean and the proterozoic are collectively called the "Precambrian"
The proterozoic started at 2.5bya and ended at 538 mya
It is the largest eon
The Great oxidation event, the emergence of the first eukaryotes and the first multicellular life was during this eon
The first glaciation occurred during this eon
The phanerozoic started at 538 mya and is still ongoing
It started at the cambrian explosion which was a period where complex life emerged
Niche:
Combination of living and non-living resources that are used to survive
The timeline of major biological events
The precambrian
Earth formed around 4.6 billion years ago(4.6bya)
During the earliest time of the planet, Earth faced many collisions with other bodies which heated it up
After the collisions slowed down, the outer layercrust cooled down but the core remained very hot even till today
4.4bya there were still collisions, there was no oxygen in the atmosphere, volcanoes were active
It became cool enough for some water vapor to turn into liquid, forming the first seas
In the seas and the atmosphere, a concoction of chemicals like,
nitrogen and its oxides, carbon dioxide, methane, ammonia, hydrogen and its sulphide and others
With the help of heat and lightning and other stuff led to the creation of small organic molecules,
Then by an unknown process to the formation of life occurred
The first life was a collection of chemicals surrounded by a membranePhospholipids spontaneously form bilayers in water
Over time, some of the chemicals developed into amino acids and eventually RNA, probably the first genetic material
This collection of chemicals organised inside a membrane collectively is called a protobiont or protocell
The proto cell likely began to grow, split and replicate until an error caused the first DNA to form
As DNA has 2 strands, it is more stable than the single stranded RNA
The protocells gave rise to the prokaryotes, which have no nuclei
The first prokaryotes were probably similar to the archaea found in hydrothermal vents
This occurred around 3.9 to 3.5 bya during the "Archean eon",
Around 2.1bya, the amount of atmospheric oxygen increased from very little to 10%
This is due to the cyanobacteria and occurred in a very short amount of time geologically speaking
This event is the "Great Oxidation Event" and resulted in th extinction of many archaea
The event was likely a mass extinction but the lack of fossil evidence prohibits it being definitively classed as a mass extinction
2.1bya marked the emergence of the first eukaryotes
Eukaryotes are thought to have evolved due to Endosymbiosis
Endosymbiosis is where one prokaryote parasitized another prokaryote or incompletely digested it
This lead to the formation of a single celled organism with organelles
The organelles developed were the mitochondria and the plastids
This lead to more complex life
1.5bya multicellular life emerged, the first probably being algae
Cambrian explosion:
The event that lead to the formation of complex multicellular life and very high diversity in animals
The cause is unknown but the event is of major significance
Some animals use minerals to make skeletons, shells
Others acquired claws, others still developed defensive plates
500mya in the mid cambrian period land plants emerged,
By the end of the cambrian, arthropods had adapted to land
Fungi were theorized to go onto land during the cambrian but recent fossil evidence suggest that they may have been on land as early as 1000mya,
Devonian
During the devonian period,
Arthropods fully terestrialised,
The ancestors of tetrapods diverged from the from the lobe finned fish
Fishes, especially jawed, had a massive amount of diversity in this period, leading to its other name "Age of fishes"
Carboniferous period:
Carboniferous period was from 359mya to 299mya
The first tetrapods emerged during this period
The forests were incredibly dense and widespread and turned into coal
The forests led to 35% atmospheric oxygenModern day oxygen is 21%
Due to the lack of carbon dioxide, the planet cooled and the temperature was too cold for the forests
The carbon from the forests sunk into swamps and locked in rocks turning into coal
Permian period:
It lasted from 299mya to 251mya
Pangaea was formed during this period
Gymnosperms evolved during this time
Archosaurs, the ancestor of dinosaurs, showed up
The permian triassic extinction
252mya, the permian-triassic extinction event occurred
It is the most severe extinction event
During this 81% of marine species and 76% of terrestrial vertebrate species went extinct
53% of all taxa and 83% of all genus went extinct
This is the largest known mass extinction of insects
The causes is not known but consensus is that the main cause was due to the volcanic eruption that created the siberian traps
Dinosaurs:
Dinosaurs evolved during the triassic due to the lack of competition for resources due to the permian triassic extinction
Due to the lack of other creatures occupying niches, many dinosaurs filled those niches
By the jurassic period(199mya to 145mya),
Huge herbivorous dinosaurs,
Smaller carnivorous dinosaurs,
Oceans full of giant squids, ichthyosaurs, plesiosaurs,
Air full of pterosaurs, the first birds and,
Small mammals had emerged
Dinosaurs thrived until they went extinct 65mya due to asteroid impact leaving only the birds as the last remaining dinosaurs
After the dinosaurs went extinct, mammals and birds took over the ecosystem and eventually led to the modern faunaAll animals in a particular region/time period and floraAll plants of a particular time period/region we see today