In the previous tutorial we paused our story of Earth’s history at the end of the Proterozoic
eon, and the Cambrian explosion.
The first era of the Phanerozoic Eon is the Paleozoic Era, which lasted from 541 to 252
million years ago.
It was a time of great change, and many new types of organisms evolved during the Paleozoic.
The Burgess shale provides a detailed look into the strange creatures of the time, like
Hallucigenia.
Nature experimented with a wide variety of different body designs during the Cambrian,
many of which went extinct.
A factor that influenced the rapid radiation of animals was the lack of predators during
and immediately after animals first evolved, which allowed for large populations since
they were not hindered by predation.
Life began in the oceans, and by the Early Phanerozoic, was beginning to invade the barren
lands, pioneered by the first vascular plants, which were later followed by lungfish and
other creatures looking for new food sources.
The colonization of land by vascular plants had a large impact on the climate by absorbing
CO2 from the atmosphere, which cooled the Earth so much that it caused a mass extinction
event.
Land plants laid the foundation for brand new ecosystems, as other organisms moved into
forests looking for food and shelter, the most consequential being a population of lungfish
that evolved leg-like fins.
These new animals, amphibians, were the first vertebrates to walk on land.
All vertebrates, from dinosaurs to humans, share a common ancestor with amphibians.
Before long, the land was colonized by amphibians, which evolved into reptiles near the end of
the Paleozoic.
The main innovation that marks the evolution of amphibians to reptiles was the rise of
the amniote egg.
It allowed reptiles to reproduce on dry land, whereas amphibians must return to water for
this part of their life cycle.
The Paleozoic was a time of great mountain building along Eastern North America.
North America collided with three separate land masses, causing three separate orogenies,
or mountain building events.
The first orogeny is called the Taconic Orogeny, occurring 450 million years ago.
The second is called the Acadian Orogeny, at 380 million.
And the third and final orogeny, called the Alleghanian Orogeny, occurred 300 million
years ago and was responsible for forming the Appalachian Mountains.
These mountains were around the size of the Himalayas when they first formed and have
extensively eroded over the past 300 million years, leaving behind the resistant stumps
of a once great mountain range.
The Alleghanian orogeny concluded with the assembly of the supercontinent Pangea at the
end of the Paleozoic.
An important geologic period toward the end of the Paleozoic Era is called the Carboniferous
Period.
A geologic period is a more specific classification of geologic time compared to an era.
The Carboniferous Period is named for the large deposits of coal that were formed during
this time, deposits that span the entire globe.
Coal forms when plant tissues are rapidly buried in anoxic conditions in coastal and
inland swamps.
Rapid burial of organic material requires rapid fluctuations in sea level, which are
caused by the formation and melting of glaciers, so without Carboniferous glaciers, the Industrial
Revolution may not have occurred!
In summary, the Paleozoic Era was a time of dramatic transformation, for both the Earth
and its inhabitants, so it seems only fitting that the era would go out with a bang.
Let’s move forward and find out precisely what happened to prompt the next era of the
Phanerozoic Eon.