PRECAMBRIAN SUPEREON
➔ Covers so much time where not a lot happened, that its called a Supereon, because
of the sheer amount of time that passed (from 4600 million years ago with the
formation of the earth to 541 Million years ago) so this time period is 4061 million
years long, which is still a ridiculously long time
HADEAN EON
➔ Called this because it looked a lot like the underworld
➔ Around 45 million years after the planets first began to form, the Moon formed.
Probably a large planetoid, about the size of Mars, crashed into the Earth. Little bits
of hot rock splashed off during the crash and orbited around the Earth. Eventually,
these bits joined together, cooled off, and became the Moon.
➔ Around 4.4 billion years ago, most of the planetoids had gotten smashed up into
dust or had become part of a bigger planet. There weren’t any more of them to
smash into the Earth. Now that planetoids weren’t always smashing into them, the
Earth and the Moon formed rocky crusts of silica all over them. The oldest Earth
rocks and Moon rocks we know about both date to this time. These are igneous
rocks like granite and quartz.
➔ The oceans formed
As the Earth cooled down, about 4.3 billion years ago, the steam in the atmosphere
also cooled down and fell as rain on the Earth. That made the oceans. By 4.2 billion
years ago, Earth had land and oceans just as it does today. Plate tectonics may have
already been moving the land and oceans around.
➔ The oceans in some parts of the Earth may even have been frozen into ice, as the
North and South Poles are today. Inside the oceans, amino acids from space began to
join together into the first proteins – not yet life, but a step along the way. Probably
the earliest RNA molecules also formed at this time.
ARCHEAN
➔ At the end of the Hadean Eon and the beginning of the Archaean Eon, about 3.8 billion
years ago, Earth was still about three times as hot as it is today, but it was no longer
hot enough to boil water.
➔ Most of the Earth was covered with oceans, and Earth’s atmosphere was mainly
carbon dioxide with very little oxygen in it. Just a little bit of land was forming as
volcanoes began to poke out of the water.
➔ Most of the rocks were igneous or metamorphic like granite or quartz. But the
earliest sedimentary rocks like sandstone also formed, mainly in the oceans, during
this time
➔ About this time – around the beginning of the Archaean Eon, about 3.8 billion years
ago – the earliest living cells formed on Earth. These cells all lived in the oceans,
which were probably much warmer and more acidic than they are now.
➔ By about 3.5 billion years ago, these early cells had evolved into simple prokaryote
cells. For the rest of the Archaean Eon, there were only prokaryote cells on Earth (and
the vast majority of cells on Earth are still prokaryotes).
➔ Photosynthesis gets started
By three billion years ago, some of these prokaryote cells evolved to be able to make
their own food out of sunlight, water, and carbon dioxide. We call this process
photosynthesis.
➔ Cells that got their energy by photosynthesis excreted (pooped out) oxygen, and once
a lot of cells were photosynthesizing there started to be more and more oxygen on
Earth.
But during the Archaean Eon almost none of that oxygen was in the atmosphere –
instead, iron and sulfur rocks mixed with early oxygen atoms to make rusty red rocks
and limestone.
➔ Millions of one-celled creatures with silicon and oxygen in their cell walls –
prokaryotes – died and sank to the bottom of the ocean, where the silicon and oxygen
was squashed into chert and flint.
PROTEROZOIC EON
➔ Two and a half billion years ago, the Archaean Eon ended and the Proterozoic Eon
began. Trillions of prokaryote cells lived in Earth’s oceans. Some of these cells could
photosynthesize their energy from sunlight, water, and carbon dioxide.
➔ These photosynthesizing cells pooped out a lot of oxygen. By about 2.3 billion years
ago, the iron and sulphur rocks of Earth had soaked up all the oxygen they could use.
More and more left-over oxygen was floating around in Earth’s atmosphere. ​FIRST
TIME AEROBIC LIFE OVERTAKES ANAEROBIC LIFE
➔ By two billion years ago, a few cells had evolved that could use all this oxygen in the
atmosphere to get energy. Eukaryote cells didn’t evolve to be able to use oxygen or
photosynthesize themselves. Instead, eukaryotes captured the smaller cells that
could photosynthesize and worked with them. Gradually these smaller cells lost the
ability to live independently and turned into mitochondria and chloroplasts. The
eukaryotes got more and more complicated. They also evolved to be able to
reproduce through meiosis, with both a father and a mother, instead of only by cell
division (mitosis).
➔ A billion years later, one billion years ago, plate tectonics brought the continents
together into one big supercontinent we call Rodinia. Then Rodinia broke apart, so
that the pieces soon began to float away from each other again. During this time, also,
there were several Ice Ages, when all of Earth was much cooler than it is today. A lot
of the water in the oceans turned to ice. Possibly for a while about 700 million years
ago the whole Earth may have been one big ball of ice. But then it soon melted again.
➔ Meiosis, or sexual reproduction, gave cells a lot more diversity in their DNA. The
diversity let evolution happen more quickly. So only a little more than a billion years
after meiosis began, the first creatures developed that had more than one cell – they
were something like hydras. That was about 600 million years ago.
➔ Around the same time, the first divisions between animals, plants, and funguses (like
mushrooms) happened. Soon there were sponges and jellyfish and flatworms in
addition to hydras, and the first multi-cellular plants like seaweed, as well.
The end of the Proterozoic, about 542 million years ago, is roughly the time when the
first segmented worms and arthropods – insects like beetles – appear on Earth. ​AGE
OF ALGAE AND BACTERIA
BEGINS PHANERZOIC EON
STARTS WITH ​PALEOZOIC ERA Age of Land Plants, Reptiles, Insects, Amphibians, Fish
CAMBRIAN PERIOD
➔ At the beginning of the Cambrian Period, about 542 million years ago, there were sea
creatures like hydras, jellyfish, sponges and seaweed living in the oceans, but only
one-celled algae on land yet. Small arthropods like beetles were beginning to appear,
and by 540 million years ago the first land plants evolved from the land algae. These
plants were like modern moss.
➔ By about 530 million years ago, some of the small beetles may have been walking
around on land, mainly on beaches when the tide had gone out. We find their tracks
in sandstone from this time. These would be the first land animals.
➔ Earth’s land was broken up into smaller continents, but they were drifting closer
together, and about 500 million years ago plate tectonics brought all of the land on
Earth together to make a new supercontinent called Pannotia. During the Cambrian
period, there don’t seem to have been any more Ice Ages. Earth was probably a little
warmer than it is today, and there were no glaciers at the North or South Pole.
➔ Around this same time, evolution seems to have speeded up, CAMBRIAN EXPLOSION
so that suddenly many new kinds of animals and plants appeared on earth, evolving
from the earlier ones. This is probably because meiosis allows more mutations and
diversity in creatures’ genetics. Mollusks like snails and squid appeared for the first
time. A few animals even had spinal cords, and were something like eels. But most
animals still lived in the oceans. On land, there was still just moss, and a few beetles
close to the shore.
ORDOVICIAN PERIOD
➔ Limestone formed
Sea levels were very high during the Ordovician period, and most of the land was
pretty flat and near sea level. Because of this, when rocks eroded most of the sand or
dirt fell into the oceans. When this dust fell to the ocean floor, the weight of the water
turned it into sedimentary limestone. Most of the rock formed during the Ordovician
period was limestone. The weight of the water on the sedimentary rocks then began
to squeeze them to form the first metamorphic rocks.
➔ Pannotia and Gondwana
The supercontinent of Pannotia broke up and the continents drifted away from each
other, but plate tectonics made some of the continents drift together again into
another supercontinent, Gondwana. At the North and South Poles, there was ice.
➔ Crabs, land plants, and insects
With all this limestone falling into the oceans, the water was full of calcium, and
animals like crabs or clams or sharks began to use the calcium to build bones and
shells for themselves. The first coral reefs appeared. On land, new little green plants
like liverworts and fungi like mushrooms joined the moss, and insects like
millipedes, spiders, and scorpions continued to walk on the beaches.
➔ End of the Ordovician period
➔ End Ordovician, 444 million years ago, 86% of species lost
— Graptolite 2-3 cm length
Graptolites, like most Ordovician life, were sea creatures. They were filter-feeding
animals and colony builders. Their demise over about a million years was probably
caused by a short, severe ice age that lowered sea levels, possibly triggered by the
uplift of the Appalachians. The newly exposed silicate rock sucked CO2 out of the
atmosphere, chilling the planet.
At the end of the Ordovician period, about 443 million years ago, another catastrophe
caused most of the sea creatures to die once again. It may be that Earth became much
colder, so that permanent ice caps formed at the North and South Pole. Because so
much water was in the ice, the shallower oceans dried up and killed the creatures
that lived in them. This catastrophe marks the change to the Silurian period.
SILURIAN PERIOD
➔ The beginning of the Silurian period was about 443 million years ago. Some
environmental problem at the end of the Ordovician period (probably ice ages) killed
most of the plants and animals on Earth. The creatures that survived this extinction
were the ones that were most able to change quickly to adapt to new conditions. Then
their ability to change speeded up evolution even more than before.
➔ First branching plants on land
By 428 million years ago, the first tiny branching plant, Cooksonia, developed on
land. More and more plants lived on land. They slowly evolved to be able to move
away from the sea coasts and grow along the edges of lakes and streams.
➔ A warming period
About 420 million years ago, the big continent of Europe slowly crashed into another
continent, the beginnings of North America. The crash pushed big mountain ranges
up towards the sky, which then eroded again into the ocean. The Earth had warmed
up again since the Ordovician period and was warmer than usual, so there was more
water and less ice.
➔ The first fish with jaws
Around the same time, the first tiny fish with jaws appeared. They were descended
from earlier chordates that were more like lampreys. For land animals, there were
still just millipedes, spiders and scorpions.
➔ At the end of the Silurian period, about 416 million years ago, a bunch of smaller
environmental problems killed off a lot of plants and animals again and started the
Devonian period.
DEVONIAN PERIOD
➔ Four hundred and sixteen million years ago, when the Silurian period ended and the
Devonian period began, most of the land on Earth was clumped together into a
supercontinent called Gondwana. At this time the only creatures that lived on land
were small plants like moss and lichens, mushrooms, and other fungi, and tiny
arthropods like millipedes, spiders, and scorpions. In the oceans, there were many
more creatures ranging from clams to crabs, octopuses, and fish, and lots of seaweed
too
➔ About 375 million years ago, some of the fish developed legs and began to walk on
land. These amphibians were the first animals with spinal cords to leave the water.
Near the end of the Devonian period (360 million years ago), some larger and more
complicated plants evolved on land too. These were mainly ferns. Some giant ferns
were as big as trees, so that a lot of the land now became covered with thick, tall
forests of giant ferns and mosses, and even a kind of fungus that could grow eight feet
tall. But the very beginnings of plants with seeds, and even flowering plants, were
also getting started at the end of the Devonian period.
➔ The Devonian period, like the Cambrian and the Silurian, ended with a crisis that
killed off most of the plants and animals that were on Earth at that time. This was
about 359 million years ago. Nobody knows what caused the crisis – it might have
been global cooling or a lot of volcanoes erupting, or a comet hitting the Earth. Nearly
all of the early fish except the coelocanths died, and most of the relatives of lampreys
(except the lampreys themselves). The next period was the Carboniferous Period.
➔ Late Devonian, 375 million years ago, 75% of species lost
— Trilobite, 5 cm length
Trilobites were the most diverse and abundant of the animals that appeared in the
Cambrian explosion 550 million years ago. Their great success was helped by their
spiky armour and multifaceted eyes. They survived the first great extinction but were
nearly wiped out in the second. The likely culprit was the newly evolved land plants
that emerged, covering the planet during the Devonian period. Their deep roots
stirred up the earth, releasing nutrients into the ocean. This might have triggered
algal blooms which sucked oxygen out of the water, suffocating bottom dwellers like
the trilobites.
CARBONIFEROUS PERIOD
➔ With the end of the Devonian period about 359 million years ago, the Carboniferous
period got started. Most of the land on Earth was warm and swampy, which was good
for ferns, so that the continents were covered with big forests of ferns. When these
ferns died, they formed thick layers of dead plants that eventually turned into coal.
➔ Most of the coal in the world today comes from ferns that grew during the
Carboniferous period. So much carbon got used up making coal that there wasn’t
enough to combine with oxygen to make carbon dioxide, and instead the oxygen
atoms had to just make oxygen molecules. Because of that, oxygen levels in the
atmosphere rose much higher than before (and higher than they are now).
➔ Plate tectonics caused the Euramerica continent to smash into Godwanaland, pushing
the land up to make the Appalachian Mountains that run along the Atlantic coast of
North America. Asia also ran into the other side of Europe to make the Ural
Mountains. These are some of the oldest mountains that are still around today. A
third mountain chain rose up in the Rocky Mountains at this time, but it’s pretty much
all eroded away now, and replaced by later Rocky Mountains.
➔ Although insects and spiders had already been living on land for many millions of
years, now some insects began to fly like flies or dragonflies. Animals with backbones
were just beginning to get started on land. These earliest animals, amphibians like
frogs, had to go back to the ocean to lay their eggs. The frogs evolved to eat insects,
because that was the only kind of land animal there was at this time.
➔ But by about 310 million years ago, the climate was changing. It was getting much
drier and hotter on land. So the plants and animals evolved to take advantage of that.
Some early pine trees developed the ability to make seeds, so they could make baby
pine trees even where there wasn’t any water for their spores. And, in the same way,
some of the amphibians developed into reptiles with the ability to lay eggs with hard
calcium shells, so they could lay eggs on land in dry places and didn’t need to stay
near the water anymore.
The end of the Carboniferous period was about 290 million years ago, when the
Permian period began.
PERMIAN PERIOD
➔ About 290 million years ago, the Carboniferous period ended and the Permian period
began. Almost all of the land on Earth grouped together in one big supercontinent we
call Pangaea, which reached all the way from the North Pole to the South Pole. With
all the land grouped together, the climate got drier. That was bad for water-loving
plants and animals like ferns and frogs. But it was good for dry land plants and
animals, so there got to be a lot more dry land creatures. The first reptiles were
already living on land, but during the Permian period there got to be many more
reptiles, and more different kinds of reptiles.
➔ At the same time, more and more pine trees also spread all over the land. It was easy
for these trees and reptiles to spread over all of the land, because it was all joined
together in one big continent.
➔ At the end of the Permian period, about 248 million years ago, there was an even
bigger catastrophe than ever before. This may have been a giant volcanic explosion in
what is now Siberia. It wiped out more than 95 percent of all life in the oceans, and
about 70 percent of life on land, both plants and animals. This catastrophe is the end
of the Permian period, and the next period is the Triassic period.
➔ End Permian, 251 million years ago, 96% of species lost
— Tabulate coral, 5 CM
Known as “the great dying”, this was by far the worst extinction event ever seen; it
nearly ended life on Earth. The tabulate corals were lost in this period – today’s corals
are an entirely different group. What caused it? A perfect storm of natural
catastrophes. A cataclysmic eruption near Siberia blasted CO2 into the atmosphere.
Methanogenic bacteria responded by belching out methane, a potent greenhouse gas.
Global temperatures surged while oceans acidified and stagnated, belching poisonous
hydrogen sulfide. “It set life back 300 million years,” says Schmidt. Rocks after this
period record no coral reefs or coal deposits.
MESOZOIC ERA: AGE OF DINOSAURS AND BIRDS
TRIASSIC PERIOD
➔ During the Triassic period (about 248 to 199 million years ago), most of Earth’s land
continued to stick together in one big supercontinent, Pangaea. Because the middle of
Pangaea was so far from the oceans, it was very dry there, like a desert. The whole
world was generally pretty warm all through the Triassic period. Even at the North
and South poles, there wasn’t any ice
➔ Because it was warm and dry, the older plants like giant ferns didn’t do well in the
Triassic. They needed wet ground for their spores to make new plants. Most of the
ferns died out, while the new pine trees took over as the main plants on Earth, even at
the North and South poles. Ginko trees also developed, and possibly the first flowers
➔ The types of plants and animals were different in southern Pangaea than they were in
the north. In the south, there were a lot of warm-blooded reptiles, but the north had
more cold-blooded reptiles like the turtles that evolved about 215 million years ago.
Throughout this period, the cold-blooded reptiles generally did better than the
warm-blooded reptiles.
➔ But at the very end of the Triassic, about 200 million years ago, the warm-blooded
reptiles evolved into the first flying reptiles – the pterodactyls. Oreptirethers evolved
into the first mammals. Another catastrophe that killed many types of plants and
animals about this time (possibly because of big volcanic eruptions as Pangaea began
to pull itself apart) marks the transition to the Jurassic period.
➔ End Triassic, 200 million years ago, 80% of species lost
— Conodont teeth 1 mm
Palaeontologists were baffled about the origin of these toothy fragments, mistaking
them for bits of clams or sponges. But the discovery of an intact fossil in Scotland in
the 1980s finally revealed their owner – a jawless eel-like vertebrate named the
conodont which boasted this remarkable set of teeth lining its mouth and throat.
They were one of the first structures built from hydroxyapatite, a calcium-rich
mineral that remains a key component of our own bones and teeth today. Of all the
great extinctions, the one that ended the Triassic is the most enigmatic. No clear
cause has been found.
JURASSIC PERIOD
➔ When the Jurassic period began, about 199 million years ago, a lot of animals had just
become extinct in the catastrophe that ended the Triassic period. This left room for
the dinosaurs to have a lot of baby dinosaurs. Soon all different kinds of dinosaurs
were living all over the Earth. The Jurassic is the main period of the dinosaurs – that’s
why they called the movie “Jurassic Park”.
➔ At the same time, near the beginning of the Jurassic period, the supercontinent
Pangaea broke up into smaller continents. These continents started to drift away
from each other. Some tectonic plates crashed into each other and formed, for
example, the Andes mountains in South America.
➔ So some of the dinosaurs and early mammals were isolated from the others. Different
kinds of animals evolved on each smaller continent. But as Pangaea broke up, the dry
heat of the Triassic became a more rain forest kind of climate. The climate stayed
warm, as in the Triassic period. There don’t seem to have been any ice ages, or any ice
at the North or South Poles. In warmer areas, the plants were mostly ferns. In colder
areas there were a lot of pine trees and ginkgo trees.
➔ Later in the Jurassic, about 150 million years ago, the first birds evolved from small
flying dinosaurs (but not from pterodactyls). Like the pterodactyls, the birds were
warm-blooded.
There was no catastrophe this time, but the Jurassic period gradually changed into
the Cretaceous period about 145 million years ago.
CRETACEOUS PERIOD
➔ During the Cretaceous period, beginning about 145 million years ago, the continents
continued to drift away from each other, so that the mammals, birds, and dinosaurs
on different continents evolved separately and got more and more different from
each other. As the continents separated, the climate got cooler and rainier, and there
was even snow in some places and glaciers on high mountains.
➔ But by the middle of the Cretaceous period, the movements of the tectonic plates
caused a lot of huge volcanic eruptions all over the planet, and these volcanoes shot a
lot of carbon dioxide into the air. The greenhouse effect of all this carbon dioxide
warmed up the planet again, so that dinosaurs were able to live even close to the
South Pole.
➔ Flowers and flowering trees and grasses got to be more and more common during the
Cretaceous period, helped along by the evolution of bees that carried pollen from one
flower to another, and by the end of the Cretaceous most of the plants on earth were
flowering ones. In addition to the bees, a lot of other new kinds of insects developed,
like ants, grasshoppers, and termites.
➔ Dinosaurs were the main kind of land animal all throughout the Cretaceous period.
Mammals were still small and there weren’t very many of them. Birds, on the other
hand, did very well, and pretty much pushed aside the older pterodactyls by the end
of the Cretaceous period. Some of these birds ate the new insects; others ate small
mammals or fish.
➔ About 65 million years ago, the Cretaceous period suddenly ended when a huge
meteorite smashed into the Earth. It hit part of what is now Mexico and made an
enormous crater more than 110 miles across (180 kilometers). The meteorite itself
must have been more than six miles across (10 km). Nearly all of the dinosaurs died –
snakes and crocodiles were among the few reptiles to survive. But some of the
mammals and birds also survived into the Tertiary period.
➔ End Cretaceous, 66 million years ago, 76% of all species lost
— Ammonite 15 cm length
The delicate leafy sutures decorating this shell represent some advanced
engineering, providing the fortification the squid-like ammonite required to
withstand the pressure of deep dives in pursuit of its prey. Dinosaurs may have ruled
the land during the Cretaceous period but the oceans belonged to the ammonites. But
volcanic activity and climate change already placed the ammonites under stress. The
asteroid impact that ended the dinosaurs’ reign provided the final blow. Only a few
dwindling species of ammonites survived.
CENOZOIC ERA: AGE OF MAMMALS AND BIRDS
TERTIARY PERIOD
➔ The Tertiary period begins with the catastrophe that killed off the dinosaurs at the
end of the Cretaceous Period, about 65 million years ago. And the Tertiary lasts down
to 1.8 million years ago.
➔ Mammals become more common
With nearly all of the dinosaurs gone, there was plenty of room on Earth for the
mammals to have lots of babies, and soon there were all different kinds of mammals
all over the Earth. About 56 million years ago, the first primates evolved – the
ancestors of today’s monkeys and people.
➔ About six million years ago, the first people evolved out of the early primates in
Africa. By 2.5 million years ago, these people were using stone tools and entering the
Paleolithic period of human history.
➔ Finally, the Tertiary period ended. The planet got cool enough to cause the last big Ice
Age, about 1.8 million years ago. The next age is the age we’re still in now; we call it
the Quaternary period.
QUATERNARY PERIOD
➔ The Quaternary period began about 1.8 million years ago (1,800,000 years ago),
coming after the Tertiary. The Quaternary is still going on today – we live in the
Quaternary period. So far, it’s a much shorter period than the others.
➔ Stone tools and Ice Ages
At the beginning of the Quaternary period, early people in Africa were already using
stone tools. The climate was mostly on the cooler side, with ice ages coming and going
every forty thousand years or so. There were big ice caps at the North and South
Poles, as there are today. Among the bigger mammals were saber-toothed tigers,
mammoths and mastodons, small ancestors of horses, and wolves.
➔ A million years later, about 800,000 years ago, people began using fire to cook their
food. These people gathered fruit and roots and grains, and scavenged meat left over
by other animals. They caught a lot of fish, and gathered mussels on sandy beaches.
➔ About 12,000 years ago, the end of this most recent Ice Age left Earth in a time when it
was warmer than usual and wetter, and everything grew really well. Many large
mammals that were adapted for the cold died out, maybe because of the climate;
more likely because people hunted them to extinction. The animals that disappeared
included saber-tooth tigers, mammoths, and mastodons. In North America, horses,
camels, and cheetahs died out too, but horses lived on in Central Asia and camels
survived in South America. ​The animals died off due to climate change associated
with the advance and retreat of major ice caps or ice sheets.
The animals were exterminated by humans: the "prehistoric overkill hypothesis"
(Martin, 1967).[14]