The Epic History of Life on Earth

Sorry, My original post on this got lost : ( Something happened to it... I don't know what... So I had to write it all over again... which sucks because it took me like 8 hours to do my original post...

The Planet we live on is truly unique; not only because there is liquid water on it's surface, but because it has something extraordinary: life.

The Earth is Born
4.6 billion years ago, there was a big nebula cloud near the edge of the Milky Way, where a solar system was just beginning to form. With the swirling gas and rocks, the Sun, four rocky planets, four gas giants, a number of dwarf planets, and an asteroid belt were just beginning to form.

Earth beginning to form, No Copyright intended, from thenakedscientists.com

(Click "Read More! >>" to learn more about the history of life on Earth, and see more cool pictures too!)
The link is right under this

Proto-Earth in the Precambrian Era

The Hadean and Archean Eons

4.54 billion years ago, Proto-Earth has just formed.  But so far it's nothing like it is today.  There's no oxygen in the air, and there's no ozone layer, so the Sun's harsh poisonous ultraviolet rays hit down on the Earth's surface.  The Earth is continually being bombarded with meteorites.  Volcanoes are continually exploding and spewing out lava.  Any possible water on the planet cannot get into a liquid form because of how extremely scorching hot it is on the planet.  You'd definitely wouldn't want to live here.

proto-earth in Hadean eon, no copyright intended, from clccharter.org

4.52 billion years ago, scientists believe that the Earth had gone through a giant impact, in the Giant Impact Hypothesis.  They believe that it crashed into a another planet, sometimes called Theia, that was about the size of Mars.  The ejected rock and material then was then flung into space, and after a while, started coming together into what we know today as the moon.  It gained enough gravity to make itself into a spherical ball, as all planets and stars do when big things have large gravitational pulls in their center.

Big Whack forms moon, no copyright intended, from photobucket.com

After the giant impact, the Earth cooled quickly.  It soon developed it's atmosphere afterwards as gas from Earth's intense core escaped through vents and volcanoes.  Comets were hitting the Earth now as well, enriching the Earth itself, possibly bringing it water, carbon dioxide, methane, nitrogen, and other volatiles.  As the planet continued to cool, clouds began to form, and with clouds came rain, which therefore formed Earth's first oceans.  Meanwhile, plate tectonics were beginning to form, forming the first continents as well.

origin of life, no copyright intended, from theresilientearth.com

3.5 billion years ago, the origins of life were just beginning.  No one's really sure how life really started though.  Some believe that the chemical mixture of life originated from Earth, while other believed it came from space, probably brought by comets.  Either way, we know that the first life forms were being created.  The four basic elements that are really necessary for life were carbon, hydrogen, oxygen, and nitrogen (CHON).  With that, DNA was created.  However, the only life here were prokaryotic cells, or bacteria, and probably some simple algae.

chemicals for life, no copyright intended, from 1.bp.blogspot.com

Proterozoic Eon

Another 0.5 billion years later, at 3 billion years ago, cells were beginning to evolve.  Before then, all cells used surrounding organic material as raw material and their energy source.  But now photosynthetic bacteria, also known as cyanobacteria, were forming.  These new lifeforms used the Sun for their energy, just as how plants use photosynthesis to make their own food.  But the most significant change that these cells made was that they added oxygen to Earth's Atmosphere.  This formed the Ozone layer which blocked harmful radiation from the Sun, allowing life to move onto land.  However, there was also a downsize to this.  Life was not used to oxygen in the air, as it was toxic.  Only the resistant forms survived and thrived, as some developed the ability to use oxygen to increase their metabolism and obtain more energy from the same food.

Cyanobacteria, no copyright intended, from ucmp.berkeley.edu

During the Proterozoic,  because of the increase in oxygen, Earth came to it's first big ice age.  Some scientists believe that Earth became a Snowball Earth, where the Earth was completely frozen from poles to equator.

Snowball Earth, no copyright intended, from brainmind.com

Around 2 billion years ago, life started evolving even more.  The first eukaryotic cells began appearing, which is a big jump from prokaryotic cells.  They were much larger and more complex from prokaryotes.  They had a nucleus, internal membranes, mitochondria and plastids, and a cytoskeletal structure.  A similar change happened when the photosynthetic cyanobacteria started going into other larger cells and becoming chloroplasts.

Eukaryotic cells, no copyright intended, from ebi.ac.uk

Keep in mind at the same time, the supercontinent Rodinia was also beginning to form at around 1.1 billion years ago.  At around 1 billion years ago, green algae was also emerging, which could be considered the first multicellular creature on Earth.  But true multicellular lifeforms probably didn't truly emerge until 900 million years ago.

Proterozoic Earth, no copyright intended, taken from corzakinteractive.com/

The Phanerozoic Era: Life is Flourishing

The Paleozoic Era

     Cambrian Ordovician Silurian Devonian Carboniferous Permian

The Cambrian period is the first period in the Phanerozoic Era, and it all began with the Cambrian Explosion, 542 million years ago.  Life normally evolves slowly, but at this time, there seemed to be a sudden "explosion" of life on Earth.  This marks a significant stage in Earth's history, where life was really jump started.  Many invertebrates appeared, as many had developed hard shells or hard body parts.  There were many molluscs, echinoderms, crinoids, and arthropods.  Among one of the most wide spread and diverse animals during this time was the trilobite.  Did you know they had some of the first eyes?  The first fish were also emerging in this period.  An ancestor of the fish was probably the pikaia.  At this point there weren't really any plants, except for algae and lichen.

Cambrian Explosion, no copyright intended, from astrobio.net

Life continued to evolve and flourish in the Ordovician period.  One of the biggest predators at the time was the nautiloid.  Molluscs and arthropods were dominating the oceans.  Reefs have started growing, which was important for the ocean ecosystems.  But by the end of the Ordovician, glaciers began covering the Earth, causing an ice age.  This would be the main cause for Earth's first major mass extinction, the Ordovician-Silurian mass extinction.  Over 60% of all marine species died off.

Ordovician ice age, no copyright intended, from answersincreation.org

The next period to come was the Silurian.  After the mass extinction, there was room for fish to evolve.  Jawed and bony fish starting appearing, which is a big evolutionary milestone.  Meanwhile, small vascular plants started appearing as well, starting the first terrestrial life, or life on land.

Silurian ocean, no copyright intended, from universe-review.ca

The Devonian was the next period to come.  It's here where plants first really dominate the land, and seed-bearing plants are found now too.  And without any land animals to eat the plants, they spread into extension forests.  The first ray-finned and lobe-finned bony fish also appeared.  Various arthropods have become terrestrial too, moving onto land.  In the oceans, primitive sharks were becoming more numerous, ammonite mollusks were appearing, and reefs and trilobites were still common.  Then the Earth's second great mass extinction came: the Late Devonian Extinction.  No one's really sure about the cause of this extinction, but it was pretty significant, especially to the reef-builders.

Dunkleosteus in Devonian period, no copyright intended, from University of Texas, Arlington

Following the Late Devonian Extinction comes the Carboniferous period.  By now, terrestrial life has been well established.  The lobe-finned bony fishes evolved into early amphibians, which are now the dominate land vertebrates.  Arthropods, which were much larger than today's, were also common, such as cockroaches and giant dragonflies.  Coal beds were very characteristic of this period, which were created from dying rainforests that rotted into the ground.  In the middle of this period was also a small mass extinction, caused by climate change.

Carboniferous swamp, no copyright intended, from nationalgeographic.com

The Permian was the last period in the Paleozoic Era.  Therapsids (the ancestors of mammals), turtles, lepidosaurs (reptiles with overlapping scales), and archosaurs (the ancestors of crocodiles and birds) were characteristic of this period.  The world at this time was hot and dry, and the world was now into one supercontinent known as Pangaea.  The extensive rainforests of the Carboniferous were gone, and now it was mostly desert.  The Permian ended with the greatest mass extinction in history: the Permian-Triassic Mass Extinction, also known as the Great Dying.  No one is really sure about the cause of this extinction, but it was probably a combination of an asteroid impact, volcanism, methane hydrate gasification, sea level fluctuations, anoxia, and hydrogen sulfide emissions.  90% of all marine living things, and 70% of all land organisms died!  And so this Great Dying ended the Paleozoic Era.

Nautiloids in the Permian Extinction, no copyright intended, from startswithabang.com

The Mesozoic Era

     Triassic Jurassic Cretaceous
This is probably the most famous era in Earth's history, and the one your most familiar with. Yes, this is the Age of Dinosaurs.

With the Permian-Triassic Extinction, the world starts out pretty damaged in the Triassic.  The first half witnesses life slow comeback to life, and we find that archosaurs, or reptiles, rise to dominance.  That's why this period is known as the Age of Reptiles.  The first true mammals started appearing here, and the first flying vertebrates as well, the pterosaurs.  It was mostly hot and dry during this period, but as Pangaea started to split apart - Laurasia in the North and Gondwana in the South, the climate started to get cooler and wetter.  At the end of the Triassic, Earth experienced it's fourth major mass extinction: the Triassic-Jurassic Mass Extinction.  Many animals were wiped out.

Pterosaurs, no copyright intended, from nationalgeographic.com

As the Jurassic period approached, dinosaurs really start to dominate.  By now, there were now two land masses - Laurasia and Gondwana (mentioned in the paragraph before).  This caused a more humid, tropical climate.  The arid deserts were replaced by lush rainforests.  Dinosaurs were dominating now, from carnivorous theropods to massive, herbivorous sauropods.  The first birds also emerged in this period, evolving from theropod dinosaurs.  Marine reptiles like ichthyosaurs and plesiosaurs ruled the oceans, while flying pterosaurs rule the skies.  Reptiles are everywhere.

Jurassic Sauropod, no copyright intended, from wikipedia.org

The Cretaceous was the longest period in the Phanerozoic Era, spanning 80 million years, and also marked the end of the Mesozoic Era.  There was a relatively warm climate and high sea level during the time as dinosaurs continued to dominate the land.  The seas were populated by marine reptiles, ammonites, and rudists.  At the same time, new groups of mammals and birds were appearing, as well as flowering plants.  This was pretty significant, as flowers not only helped plants spread, but also made the world more beautiful.  At the end of Cretaceous was the most famous mass extinction of the world: the Cretaceous-Tertiary Mass Extinction.  Most believe that it was caused by a giant asteroid impact, and most likely combination of other things as well, and with this, every dinosaur mysteriously disappeared and died off.

Dinosaurs, no copyright intended, taken from kids-dinosaurs.com

The Cenozoic Era

     Tertiary Quaternary
 And with the Cretaceous-Tertiary extinction event, leads us to the Cenozoic Era.  The first period in the Cenozoic was the Tertiary, or Paleogene period.  With Dinosaurs gone, the small little mammals quickly took over as the new dominating animals, leading to the Age of Mammals.  Mammals would now become more diverse than ever - taking to the oceans, trees, and land.  With the pterosaurs gone, there was now room in the sky for birds.  There were more deciduous trees now, and the first grasses were appearing.  Grasses replaced trees in many places as they were better adapted to hotter, drier areas.  Meanwhile, as the continents continued to shift, the warm tropical climate turned cooler and drier into an ice age.

Tertiary Environment, no copyright intended, from http://universe-review.ca

The ice age soon stopped, and then the Quaternary, or Neogene period had begun.  Mammals and birds continued to evolve considerably, as well as sharks and insects.  And then something spectacular happened.  Evolving from primates, the first homo sapiens appeared.  They would forever change the world.  At around 10,000 years ago, they started developing civilization, technology, religion, science, farming, and many other things.  Why, one of those homo sapiens is typing this blog and teaching you about history right now!

Evolution of Man, No copyright intended, from thechive.com

A Donut representing Earth's entire history, No Copyright intended, from wikipedia.org

BBC Life on Earth the Infinite Variety, Part 1/6

Now you know about Earth's entire history with it's unique forms of life.  And looking back, the time we've actually spent on this planet is incredibly small.  Through it's history, over 99.9% of all life that has ever lived on this planet is now extinct!  And look at the world now.  There's still so much life here!  So much to learn...

-Darren!ee