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AGE080- Week 13 Worksheet (Powerpoint: “Wonderful Earth”)
1. The Sun was formed approximately 4.6 billion years ago, in an area of the Milky
Way galaxy where an older star had exploded as a _supernova_ .
2. The Earth was formed about 4.54 billion years ago; about 4.53 billion years ago,
the __moon_____ was formed, probably because of a collision between the
Earth and a planet the size of Mars.
3. From 4.1 to 3.8 billion years ago, the Earth was hit continuously by large objects
(asteroids, comets, and meteoroids), in an event known as the __Late Heavy
Bombardment__. This event plays an important part in the thinking about the
origin of life on earth.
4. We cannot give a precise date for the emergence of life on earth, but
_prokaryotes___ (organisms that lack a cell nucleus) were present by 3.4 billion
years ago.
5. _Stromatolites_ are mats formed by blue-green algae (cyanobacteria).
6. These bacteria obtain energy through _photosynthesis_ , a process in which
oxygen is released as a waste product.
7. As a result of the activity of cyanobacteria, the Earth underwent the __Great__
Oxygenation__ Event beginning 2.4 billion years ago.
8. However, it took a long time for all the oxygen sinks in the ocean and on the
continents to be filled. Higher levels of oxygen permitted the major animal
phyla to burst on the scene in a relatively short time period 545-530 million years
ago, known as the _Cambrian_ _Explosion_ .
9. The greatest extinction in geologic history, the __Permian__ extinction (252
million years ago), caused 96% of all marine species and 70% of land vertebrate
species to go extinct.
10. During the period from ~230 – 65 million years ago, reptiles dominated the Earth.
This period, the Mesozoic Era, is popularly known as the Age of _Dinosaurs_.
11. An impact event caused when an asteroid hit the earth 65 million years ago led
to the extinction of the dinosaurs but opened the way for __mammals__ to
dominate the Earth.
12. For the last three million years, the Earth has been experiencing 100,000 year
long cycles of _glaciation_ followed by ~10,000-year long interglacial periods.
(Powerpoint: “Origin of Life”)
13. The main building blocks of proteins are __amino_______ __acids_________ ;
the main building blocks of DNA and RNA are ___nucleotides___..
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