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7th Grade - The History of Earth
Transcript of 7th Grade - The History of Earth
I am going to tell you a story about us.
This story, like any history retelling,
starts at the beginning.
Nearly 14 billion years ago...
There were no stars,
no dust and gas,
There was no universe and because there was no universe
... did not exist.
All of everything was contained in a single infinitesimally small point called a singularity.
Then through no understanding of humankind, the Universe was born.
Energy began to spew from the singularity as the singularity expanded rapidly.
Space bound into existence and at the same moment so did time.
The energy was so intense fusion of small particles like quarks, protons, electrons, and neutrons formed into matter.
The first two elements were born from this energetic birth, helium and hydrogen.
You and me and nearly everything around us is made of much more than just this hydrogen and helium. But to explain that, we have to keep going.
A billion years goes by from this initial expansion and the first star is born. It is mostly hydrogen and a little helium. It is massive as all of the first stars are because of the abundant gases available.
Stars run on nuclear fusion.
The bigger the star, the more brilliant it shines. But there is a downside to shining so bright.
The bigger the star,
the faster they fuse,
the faster they go out.
... but in the beginning there were just two
So where does everything else come from?
Its all about the fusion.
Time to go back to the stars...
This nuclear furnace will continue fusing hydrogen until all the hydrogen is gone.
Since gravity forces everything inward, the star is constantly fighting a battle between energy pushing out and gravity pulling in.
As the star loses its hydrogen, pressures pushing the star inward forces helium to fuse. When helium fuses it creates carbon, nitrogen and oxygen.
Supermassive stars like the early stars in our universe don’t just go dim.
In the last moments of their existence they go out with a spectacular display - a supernova.
Cut out at 6 minutes skipping wormhole; Vsauce black holes
Black holes are cool, but this isn't a story about that... it is a story about us.
Back to the star and its supernova.
Stephen Hawking clip: supernova from Into the Universe 5 minutes
the Crab nebula
So here we are, finally starting to become part of the story.
Our planet Earth formed from dust and gases that were left over from a star, from a collapsed nebula, that collected deep in space from ancient stars, that formed from the first elements, that formed from the initial expansion of the Universe.
Nearly 4.6 billion years ago the Earth was formed.
There was just rock, only rock.
Eventually the Earth cooled enough to allow for the formation of clouds.
It rained for thousands of years until land and ocean became two.
From the rain, the rock was chemically broken down and soil started to form.
Earth was starting to look a little more like home. Our first oceans were shallow, but it was in this first oceans that the first life sprung into existence on our planet.
Around a billion years after its first formation, life began to take place. Why? We don’t know.
About 2 bya multicellular life evolved.
1.2 billion years ago, sexual reproduction found its way through evolution.
600 million years ago, simple animals evolved up on the scene.
500 million years ago the first fish fossils appear. A little beyond that, sharks are swimming in the oceans and land plants have rooted out of the water.
400 million years ago up come insects and seeds. About 300 million years ago rise the amphibians, dinosaurs, reptiles, trees and ferns.
200 million years evolve the mammals and soon after that the birds.
130 million years ago the first flowers evolve on Earth.
It is only 60 million years ago that primates find their evolutionary path and join the scene. And that’s us, well the beginning of us anyhow. True humans (
didn’t really exist until about 200,000 years ago.
Rise and fall of megafauna
Size of a VBeetle
Life has evolved on our planet, but that isn’t the only thing that has changed over time. The Earth has changed. The Earth began as a ball of magma. Over time it hardened and layers began to form due to density. Over time land and ocean began to separate.
Not today and future today (yeah I know that doesn't make sense)
Just like regular time, but with a different name just to be confusing.
Eons, Eras, Periods, Epochs and Ages
The Permian Extinction
aka The Great Dieing
252 mya Earth's largest extinction
90% to 96% of all species (96% of all marine species and an estimated 70% of land species).
75% of all species became extinct. All non-avian dinosaurs became extinct during that time.
Cretaceous–Paleogene extinction event (End Cretaceous, K-T extinction)
Triassic–Jurassic extinction event (End Triassic): 201.3 mya
70% to 75% of all species went extinct.
Most of the large amphibians were eliminated, leaving dinosaurs with little terrestrial competition.
Late Devonian extinction: 375–360 mya
70% of all species extinct
CAUSE: Climate change, asteroid impact or volcanism
CAUSE: ??? multiple causes
CAUSE: Chicxulub impactor (meteor)
CAUSE: Global cooling and sea level drop
CAUSE: Unsure/multiple causes
What are they?
The world as it is now is not that same as it was in the past. The location and shape of our continents were once very different.
Utah is now a desert. It was in the past a tropical paradise with plants and animals typical of tropical areas.
Other times it has been so cold that glaciers were common. There have even been times where Utah was part of an ocean floor.
This is due to many factors - some being that Utah hasn’t always sat on its location of the planet at 41 degrees North.
The rock formations and fossils not only give us an indication of time, but they tell us a story of life and conditions like climate at the time that they lived.
Within the rock are the secrets and whispers of the past.
The Fossil Record
A fossil is the preserved remains or traces of animals, plants, or other organisms from the past.
Sedimentary rock is a very important type of rock for telling us about what life was like on the surface.
Rocks like limestone, sandstone, shale are great rocks because they have the ability to preserve past life, aka fossils. These rocks form in bodies of water. What could this tell us about the local conditions at the time?
Conditions have to be just right for creating a fossil. Most creatures that have existed on our planet have never been fossilized. But, a small percentage do, and from those we can put together a story of the past.
Types of Fossils
organism's preserved parts
preserved hard parts
how organism lived, imprints of bodies, burrows, etc.
Time to observe some replicas and actual real fossils.
casts & molds
What about petrified wood?
Body fossil or trace fossil?
Discuss as a group