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Cells can be classified into prokaryotes and eukaryotes. Prokaryotes are considered to be the first ever living cells, and are thought to have originated from protobionts. They are in the kingdoms of monera (simple bacteria) and archaea. Fossils proved us that both archaea and monera had evolved somewhere between 3 to 4 billion years ago.Staphylococcus, escherichia coli, and streptococcus are examples of prokaryotes.
The structure of a Prokaryote cell:
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Why were they the first form of life to appear on earth?
There are several theories suggesting how life first appeared on earth.

Millers Experiment
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inorganic substances as mentioned in the previous diagram, and recreate it first formed, andformed.
Prokaryotes and Eukaryotes, What are the Similarities and Differences?
Billions of years ago, during proterozoic period, prokaryotes came into existence and were the only form of life on earth. Over a period of time, prokaryotes evolved into more advanced cells, also known as eukaryotes.Biologists believe that eukaryotes evolved from prokaryotes because of the following similarities:

What{Ordiviciangeogr.jpeg} What Were The
Paleontologists have hypothesized that the Ordovician mass extinction was the aftereffect of glaciation, evidence for this was found on the continent Gondwana at the end of that time period. Glacial deposits and magnetic rocks were discovered in the Saharan Desert and scientists proposed a theory for the cause of the glaciation based on that data. During the Ordovician period, the continent of Gondwana moved over the North Pole, this caused the climate to cool to an enormous degree. This resulted in widespread glaciation, which also caused the sea levels all over the world to fluctuate constantly, as huge amounts of water froze into ice sheets. All these events combined together caused by glaciation could have also greatly contributed to the mass extinction of the Ordovician time period.
Another theory that is plausible, but slightly ambiguous, as there is a lack of evidence to support it, is the Gamma Ray Burst Hypothesis. Scientists based in the University of Kansas and NASA have theorized that the first exinctions during the Ordovician period may have been due to an exploding start within 6,000 light years of Earth. The a ten second burst from the aforementioned gamma ray ( which would have originated from that star) would have damaged the Earth's atmosphere badly, causing almost half of it's ozone to disappear immediately. All surface dwelling oranisms, including plants which were the planet's photosynthsizers would all be exposed to high levels of ultraviolet radiation. Not only would this cause temperatures to drop, but would also wipe out a majority of the oraganisms on Earth.

Jean-Baptiste Lamarck
Jean-Baptiste Lamarck was the first scientist to propose a theory of evolution, his theoretical observations on evolution were demonstrated in his extensive work on invertebrates (an animal that has no backbone or spinal column). Lamarck accepted the view that animals in nature were arranged on one continuous natural scale. Lamarck believed that living things evolved in a continuously upward direction, from dead matter, through simple to more complex forms, toward human. From the simplest forms of life, to more complex forms emerged naturally. These ideas were initially presented in 1809 in Lamarck's major theoretical work, Philosophie Zoologique (Zoological Philosophy), which he elaborated on them throughout his career.
Lamark's Theory vs. Darwin's Theory
Lamarck’s theory has been proven to be incorrect, while Darwin’s appears to be an accurate description of the process of evolution. Lamarck suggested that the characteristics an animal acquired in the course of its lifetime would be passed on through genetics to its offspring, and thus, over time, with the many changes each generation contributed, a species would evolve. Conversely, Darwin’s view is that a mutated characteristic is only passed on if it is useful to the survival of the animal.
- Chew, Robin. "Charles Darwin British Naturalist." 3 Mar. 2007. 12 June 2007 <http://www.lucidcafe.com/library/96feb/darwin.html>.
- Darwin, Charles. Darwin's Drawings of Variant Heads and Beaks Among Galapagos Finches. Darwin's theory of evolution. 14 June 2007 <http://www.bbc.co.uk/schools/gcsebitesize/img/bifinches.jpg>.

Prokaryotes
Eukaryotic Cells
Some guiding questions to help you write your page:
Describe the changes in the atmosphere of the earth since it condensed from the remnants of the Big Bang.
Explain how these changes occured.
What role did cyanobacteria play?
What evolutionary changes either caused our atmosphere to change, or were caused by the change in atmosphere.
NB: you can check the philiosophy, instructions and assessment criteria for this exercise.
URL of pages used: (cite later)
http://www.palaeos.com/Earth/Atmosphere/oxygen.htm

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Introduction
{http://www.randomhouse.com/catalog/covers/9780385468091.gif} The Sixth Extinction is a novel (picture on right) written by one of the world's most famous paleoanthropologist, Dr. Richard Leakey, and co-authored by science jounalist and author Roger Lewin. In this novel, Dr. Richard Leakey and science writer Roger Lewin argue that a Sixth Great Extinction of life on Earth is currently occurring. After examining The Five Mass Extinctions that have taken place before, and drawing parallels between these evolutionary crises and mankind's destruction of 50,000 species per year in the present due to several factors, they have drawn up one massive conclusion: life on Earth is in the midst of a Sixth Extinction.