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Early Earth History

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Alexis Guillory

on 20 December 2012

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Transcript of Early Earth History

photo credit Nasa / Goddard Space Flight Center / Reto Stöckli Earth's History Precambrian Time Includes the Hadean, Archaean, and Proterozoic Eons
Lasted from about 4.5 billion years ago to about 544 million years ago
Relatively litt is known about the organisms that lived during this time because the fossil record from Precambrian time is sparse
One reason is that many Precambrian rocks have been so deeply buried that they have been changed by heat and pressure
Also most Precambrian organisms did not have hard parts which would have increased their chance of becoming fossils Cyanobacteria Thought to be one fo the earlies forms of life on Earth
First appeared 3.5 billion years ago
They were important becasue they produced oxygen which helped change Earth's atmosphere
Also important because this caused the ozone layer in the atmosphere began to develop, shielding Earth from ultraviolet rays
It is hypothesized that this allow species of single-celled organisms to evolve into more complex organisms Precambrian Life-forms Invertebrates appeared toward the end of Precambrian time
Many Precambrian fossils are trace fossils
A group of animals similar to modern jellyfish, worms, and soft coral known as Edicaran fauna lived during the end of this time
These were bottom dwellers and may have become extinct around the time trilobites came around, but no one knows for sure Paleozoic Era Ranges from about 544 million years ago to about 248 million years ago
Many of the lifeforms from this time were marine Paleozoic Life Many life forms were marine
Trilobites were common
Fossil record of this era contains abundant fossils
First vertebrates evolved and were fish-like creatures
Forest began to appear and some vertebrates began to adapt to land by the Devonian Period Life on Land Paleontologists know that many ancient fish had lungs and gills to survive in water with low oxygen
One fish even had leg-like fins
Paleontologists hypothesize that amphibians evolved from this kind of fish
Later, by the Pennsylvanian Period, amphibians evolved adaptations for life completly on land
Eggs with a membrane to protect them from drying out
Skin with hard scales to pevent the loss of body fluid Mountain Building Appalachian Mountains occurred in several episodes
When the ocean separating North America from Europe and Africa began to close, causing volcanic islands to collide with North American Plate
Then later the African Plate collided with the North American Plate End of the Paleozoic At the end of the Paleozoic Era, about 85% of marine species and 70% of land species died
There are a couple of hypotheses to explain this
A change in climate and a lowering of sea level caused by the formation of Pangaea
Volcanic activity
Large asteroids or comets colliding with Earth
A combination of several or all these events happening at about the same time Mesozoic Era Occurred between 248 and 65 million years ago
Started with large single land mass Pangaea
Pangaea broke apart into two pieces during the Triassic Period
The northern part was called Laurasia and the southern part was call Gondwanaland
These later broke apart as well Species that adapted to the new environment survived the mass extinction of the Paleozoic Era
Reptiles with their shelled eggs and scaled skin were well adapted for the now much drier climate and became the most abundanct animal on land by the Triassic Period Dinosaurs The first small dinosaurs appeared during the Triassic Period and larger species appeared during the Jurassic and Cretaceous Periods
Scientists believe dinosaurs might have been warm-blooded because their bones more closely resemble warm-blooded animals than cold-blooded animals
The fossil record also indicates that dinosaurs might have nurtured their young and traveled in heards surrounding their young
Not a trait of modern reptiles Birds Appeared during the Jurassic Period
Evolved from small, meat-eating dinosaurs
Earliest bird is called an Archaeopteryx, but it had some features not shared by modern birds
It is not a direct ancestor of today's birds Mammals First appeared int the Triassic Period
Were small, mouselike creatures
They had two characteristics that enabled them to survive in many changing environments
Warm-blood and fur that covered their bodies, and females produced milk to feed their young Gymnosperms and Angiosperms Gymnosperms first appeared in the Paleozoic Era
These are plants that produce seeds but not flowers
Angiosperms are flowering plants the evolved during the Cretaceous Period
Can live in many environments
Are the most diverse and abundant land plants today
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