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From 4 Billion Years Ago to 250 Million Years Ago
Houston Museum of Natural Science has a wonderful hall of Paleontology.
We start about 4 Billion years ago when the seas were hot and acidic.
This early time is known as Precambrian.
The earliest know life was found in Western Australia encased in rock formations known as Stromatolites.
Cutting the stromatolites one way shows the tree ring markings of the microbes.
Cutting the stromatolites in the other direction shows the circular shape of the microbs.
It took about 2 billion years for the microbes to change the atmosphere from acid to air.
The microbes caused the Great Oxygen Event.
After the Oxygen Event, life grew into plant fans.
More complex life evolved into marine ferns.
About 700 million years ago, the earth froze over into, "Snowball Earth" killing or freezing most life forms.
540 million years ago the earth warmed and the Cambrian era began.
Trilobite means 3-lobed-life They were water bugs.
Trilobites are arthropods like spiders or crustaceans having external skeletons which must be molted to grow.
Trilobites had hard upper shells, but were softer underneath.
Trilobites had many legs with claws.
Trilobites developed appendages for feeling around or for defense.
Look at the "noses" on these Trilobites!
Trilobites were like pill bugs in that they would roll up if threatened.
Anomalocaris, abnormal shrimp, was the top predator and ate Trilobites.
Hallucigenia, left, was 2 inches long, had a worm like body with two rows of spikes along its back, paired tentacles act as legs.
Trilobites evolved and are therefore used by paleontologists for dating rock.
Early Nautiloids began.
Sea Scorpions, ancestor of modern scorpions, became the top predator.
Trilobites were still around with interesting appendages.
Giant placoderm (plated) fishes dominated the ocean. Their mouths had plates which were self sharpening and grew continuously.
Amphibians swam with the giant fish.
The Coelacanth is known as a "bony fish."
The Coelacanth (bony fish) was thought to be extinct until one was caught near Africa in 1938.
Tiktaalik was a transition from fish to amphibian. It was a hybrid fish/amphibian with primitive lungs.
Forests were thick with ferns, but no flowers yet. Leaves dropped and were buried eventually becoming coal.
Marine reptiles were small in the Carboniferous Period.
This is a crinoid which covered the bottom of the shallow inland sea in the Gulf of Mexico to Canada.
Armor plated "Frog-oid."
Dimetrodon lived 50 million years Before the dinosaurs. It is a synapsid, having one hole behind the eye. It was a reptile-like Mammal!
This is the fossil of the Dimetrodon. It had a large fin on the back for heat collecting, defense or attracting a mate.
Here you can better see the one hold behind the eye socket, making is a Synapsid.
Here is an amphibian of the same era as Dimetrodon.
Another amphibian of the Carboniferous Period.
This is an artists idea of what the Gorgon looked like. The Gorgon was a large mammal before the dinosaurs took over.
This is a fossil of the Gorgon, which is as big as a bear.
Look behind the eye socket, there is one hole. This is a synapsid, a mammal.
About 252 million years ago there was an extinction event. 95% loss in ocean and 70% loss on land.
What caused it: meteor, volcanoes? It took about 10 million years for the earth to get over this event.
Another Extinction Event Awaits.
We will stop with this extinction event. It is quite enough for now. Remember, there is another extinction event coming! The rest, as they say, is history.