Teacher's Notes: What your students will know by the end of this unit
I. Formation of Earth
The Earth formed from a nebular cloud about 4.6 billion years ago.
The atmosphere at the beginning of Earth's time consisted of water vapor, carbon monoxide, carbon dioxide, nitrogen, hydrogen sulfide and hydrogen cyanide.
About 4 billion years ago, Earth began to cool and the first rocks formed on the surface.
The formation of rocks lead to volcanoes. Volcanic activity dominated the surface of the Earth for millions of years. As volcanoes erupted, they released water, carbon dioxide, nitrogen and carbon monoxide through a process called outgassing. When the Earth cooled more (about 3.8 billion years ago) the outgassed water vapor in the atmosphere began to fall to the Earth's surface as liquid water. This water filled oceans and the Earth was finally ready for life to begin.
II. Evolution of Life on Earth
3.5 billion years ago, the first prokaryotes emerged on Earth. These prokaryotes were photosynthetic - they used the water and carbon dioxide to produce sugars and oxygen. Prior to this, there was very little if any oxygen present in the atmosphere. By 2.2 billion years ago, oxygen had accumulated in our atmosphere.
2 billion years ago, the first eukaryotes developed
Multicellular organisms developed next.
During the Paleozoic era (544-254 mya), earth housed the first land plants, and vertebrate and invertebrate animals.
The Mesozoic era (245-65 mya) is noted as the age of the dinosaurs, age of the reptiles, and mammals began to evolve
Cenozoic era (65 mya to present) is the age of the mammals
III. Evolution of the Planet
As the Earth changed, organisms living on the Earth changed as well. Processes such as plate tectonics and mountain building lead to physical changes on the Earth. These processes also lead to evolution of organisms. Geographical isolation is an example of an evolutionary process precipitated by the changing of the landscape of Earth.
Rocks and fossils provide evidence of the changing landscape and changing and evolving organisms throughout the history of time on Earth.