Paleontology is the study of old life forms primarily through fossils. Fossils
are any part or trace of an organism that lived long ago. Time, since the
beginning of planet Earth, is measured in geologic time units. The largest
measure in geologic time is the eon. There have been three eons:
1. Archeon, 4.6 to 2.5 BYA (billion years ago)
2. Proterozoic, 2.5 to .59 BYA
3. Phanerozoic, .59 BYA to the present.
Eons have eras. The eras of the Phanerozoic are:
1. Paleozoic
2. Mesozoic
3. Cenozoic
Eras have periods. The periods of the Paleozoic are:
1. Cambrian--Earth was dominated by bug-like creatures called trilobites
2. Ordovician--fish appeared
3. Silurian--Earth was dominated by coral
4. Devonian--Earth was dominated by fish with jaws
5. carboniferous--period in which most fossil fuels began their formation
a. Mississippian--age of crinoids
b. Pennsylvanian--age of insects
6. Permian--Earth was dominated by amphibians
The periods of the Mesozoic are:
1. Triassic--Earth was dominated by small reptiles
2. Jurassic--Earth was dominated by large reptiles
3. cretaceous--the true age of the dinosaur, and period in which they became extinct
The periods of the Cenozoic are:
1. tertiary--age of mammals
2. quaternary--age of man
Periods have epochs. The epochs of the quaternary are:
1. Pliocene--human ancestors lived
2. Pleistocene--early humans developed, ice ages came and went
3. recent--we live in the recent.
Earth is believed to be almost five billion years old. Early Earth was a hot mass which cooled to form a crust. Inside the Earth it is still very hot today. The dense parts of the Earth do not float and these form the beds of oceans. However, what we call land is less dense and floats on the liquid core of the Earth. Land formation gave rise to early continents. In the Permian, all of these continents came together to form one giant continent called Pangaea. In the Mesozoic, Pangaea began to break up into the continents of today. These continents still slowly drift about.
However, it is believed by some scientists that when the weight of one of the polar ice caps becomes imbalanced and greater than that of the other polar ice cap, the entire crust of the earth will rapidly shift. These rapid shifts can dramatically change the climate on a continent. This may be why woolly mammoth bones and bodies, animals who could only live in a warm climate, are found in Siberia.
As the earth cools, it cracks into plates. Mountains are formed by subduction.
Subduction occurs when two plates come together, pushing the land upward. This
is why the fossils of sea creatures are always found in mountains. This is also
the reason for earthquakes. When two plates slide by each other, they create
friction. As the movement overcomes the friction, the earth moves rapidly
producing an earthquake.
Life began on Earth about 3.5 billion years ago. The first form of life was probably a blue-green algae called stromatolite. However, bacteria may have preceded stromatolites. These life forms were anaerobic, as no free oxygen (O2) existed until two billion years ago. Paleontologists have found that the first rust, which requires O2, began at this time. Plant life began in the sea and moved to land as land was formed.
The first animals to dominate Earth were the trilobites. They were bug-like creatures with jointed legs. They too lived in the sea. Trilobites dominated Earth for 50 million years. However, when the fish called placoderm evolved with a jaw and paver teeth, they ate the trilobites into extinction. Sharks evolved 400 million years ago and ate the placoderm into extinction. Sharks have dominated the seas for all of their existence.
In the carboniferous, fern forests evolved with tree-like ferns which were 150 feet tall. Ferns and other swamp plants died and fell to the bottom of the swamp. As things piled up on top of them, the heat and pressure drove off the hydrogen and oxygen and all that was left was pure carbon in the form of coal. 90% of the world's coal supply was laid down in the carboniferous.
In the Mesozoic era, reptiles ruled the land. The first dominant reptiles was the crimson crock, an alligator-like lizard that ate anything they could catch. Then came the dinosaurs. Allosaurus and Tyrannosaurus Rex were dominant predators. Flying dinosaurs called Pterodactyls dominated the sky. However, most dinosaurs were peaceful herbivores, such as Stegosaurus and Triceratops. Dinosaurs are distinguished from other reptiles by the structure of their hip. The word "dinosaur" means terrible lizard.
Throughout geologic time there have occurred extinction periods during which many species of life suddenly disappeared. These extinction periods occur about ever 26 million years. These extinction periods may be the result of asteroids colliding with Earth. An examination of the earth's crust shows that thin layers of iridium, an element which only occurs in asteroids, are found deposited in soil about every 26 million years. If this is the case, the next extinction period will occur in about 16 million years. It is believed that one such extinction period killed off much of the vegetation on Earth, and therefore killed off the dinosaurs.
The first creatures like people appeared on Earth about three million years ago. Homo sapiens appeared about 500,000 years ago. People are the first animal to dominate the earth because of intellect and cooperation. People are bright and formed social units for teamwork. Humanity developed morality which allowed for even greater harmony. All progress made by humanity has been made because morality restrained our savage animal nature to allow cooperation.
Paleontologists estimate the age of fossils using techniques such as carbon
dating. It is known that life forms have the same percentage of the radioactive
isotope known as carbon 14 which exists in the atmosphere. The rate of decay of
a radioactive isotope is measured by their half-life. The half-life of a
radioactive isotope is the time needed for half of the radioactive isotope to
decay. The half life for carbon 14 is 5,730 years. Therefore, if the remains of
an organism are found which contains one half the amount of carbon 14 that is in
a living organism, the remains are 5,730 years old. If the remains of an organism
have only one fourth the amount of carbon 14, the remains are 11,460 years old.
While carbon dating is the dating technique which is best known, other radioactive
isotopes can also be used to date the remains of once living things, as well as
non-living things such as rocks.