History of Life

The Eras of Life

The Precambrian era (the prehistory of life)
Paleozoic
Mesozoic
Cenozoic
The prehistory of life is presumed through physics and chemistry but no solid statements can be made, only hypothesizes.
The eras have been classified and named by people.
Some eras or periods are separated by mass extinctions.

The Earth was formed about 4.6 billion years ago.
Chemical evolution took place.
Substances important for life were formed and began to accumulate.
Atmosphere made from lots carbon dioxide as well as nitrogen, hydrogen, ammonia and methane.
This atmosphere was very different to our modern atmosphere, which has lots of oxygen.
There was lots of lightning, UV radiation, meteor showers and volcanoes.
Simple organic compounds began forming, such as nucleotides and amino acids.
These became complex organic compounds such as nucleic acids and proteins through chemical evolution.

A membrane enclosed the building blocks for life (important substances).
A membrane is a lipid structure that allows cells to control what enters and leaves the cell.
Membranes allowed the first protocells to form.
This was the beginning of biological evolution.
Development of the first protocell made it possible for chemosynthesis (synthesis of organic molecules through other molecules, autotrophs), photosynthesis (synthesis of organic compounds through photons, phototrophs) allowed for cellular respiration.

Divided into 6 periods.
Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.
Rapid species mega evolution during the first period known as the Cambrian explosion.
Diversification of plants and animals.
The first plants and animals moved to land.
Ends with a large mass-extinction called the Permian Extinction.

Cambrian Explosion
A huge increase in the diversity of life.
Ordovician Period
Plants start to colonize land.
Animals are mainly isolated to life underwater but fish start to emerge.
Devonian Period
First seed plants which would later become the most common plant type.
Animals start to breathe air.
Carboniferous Period
Large forests, abundant oxygen in the air.
The trees would become coal we have in the modern day.
Permian Period
Pangea supercontinent forms.
Extreme temperatures led animals to evolve adaptations for hot and dry climates.

Also called the "Biological Big Bang".
Biodiversity increased rapidly.
Oxygen level at the atmosphere was very high which allowed for high amounts of cellular respiration.
Ozone (O₃) formed the ozone layer protected life from radiation.
Life still mostly in water but first plants and animals moved on land.
Almost all present-day phyla formed.
Even the earliest Chordata (Chordata is a phylum that contains creatures we traditionally consider "animals". As well as others such as anemones and sponges).

First known mass extinction was about 440 million years ago.
Presumed ice age and lowering of sea level about 100m.
85% of the species went extinct, mostly marine species.
After the first the have been 4 to 5 more mass extinctions.
Largest is the Permian-Triassic mass extinction, where 96% of all organisms went extinct, marking the end of the Paleozoic era.

250 to 65 million years ago.
Age of the dinosaurs and reptiles.
Advantages compared to amphibians were drought resistant skin, internal fertilization and skin-covered eggs.
This made them not water-dependent.
Dinosaurs dominated the Earth for over 100 million years.

Dinosaurs are the top predators and herbivores and reach immense sizes.
The largest dinosaurs such as Bruathkayosaurus matleyi are estimated to weigh around 110 to 170 metric tonnes! That's even more than a blue whale!
Aquatic reptiles dominated the water and pterosaurs dominated the sky. Pterosaurs such as Hatzegoptyrex were the size of giraffes!
All dinosaurs and prehistoric reptiles over a certain size were wiped out in the Cretacous extinction event, about 66 million years ago.
This led to a great increase in available ecological niches, which birds, mammals and to an extent reptiles would soon fill.

66 million years ago to the present.
Age of mammals.
Diversification of birds and mammals.
Mammals couldn't diversify before as ecological niches were mostly filled by dinosaurs.
Birds and mammals filled in the ecological niches that were empty after dinosaurs went extinct.
Birds and animals were war blooded and had hair, fur and feathers.
Caring of offspring gives a more efficient start thanks to nutrition.
Movement, senses, and nervous system evolves.