History of Life of Earth              
                                           
                                 
                                           
          Evolution:
the process by which living things change over a period of time.		          
                                           
    While there is no doubt that living things change over time. However, speciation - one type of organism changing into another type of organism - is very much in doubt.            
                                           
        Like other scientific theories, several people have contributed to the theory of evolution. To understand evolution, you must be familiar with many different terms. Any discussion of the topic is useless without an agreement on these terms.
Even the definition of evolutioncan be debated. 		   
                                           
  Living things change very slowly. While some changes can be observed directly, much what we know about the history of life on earth comes from the fossil record. A fossil is any trace of a long-dead organism. Most fossils are formed when sediment is deposited by wind or water. These sedimentary fossils usually develop only from hard body parts. The soft body parts decompose before they can be replaced by hard minerals. The special conditions needed for the formation of fossils cause the fossil record to be less than complete. Because of this, the fossil record is open to interpretation. Different scientists can look at the same fossil and reach different conclusions about its place in the history of life.  
       
 
Fossil imprint of an organism.
Fossil track of an organism.
  Organism preserved in amber (fossilized tree sap).      
       
     
In 1669, Nicolaus Steno proposed the Law of Superposition stating that successive layers of rock or soil were deposited on top of one another by wind or water. This means that the lowest layers are the oldest, while the top layers are the most recent. This law is still accepted today and allows scientists to give fossils a relative age.
Carbon dating can be used to determine the actual age of an abject. The only requirement is that the object must have carbon in its structure.
     
   
Species:
A group of organisms that mate and produce fertile offspring.
             
                           
       

The morphological concept of species uses the internal and external structure and appearance of organisms to determine a species. These characteristics are easy to observe, making species identification relatively convenient. The morphological concept of species has limitations. All individuals within a morphological species do not look alike.

Humans, for example, do not all look alike. We are, however, all Homo sapiens.

                           
       

The biological concept of species states that a species is a population of organisms that can successfully interbreed but cannot breed with other groups. Scientists who study evolution today do not like this definition because the reproductive compatibility of extinct organisms cannot be tested and the definition is unsatisfactory for organisms that reproduce asexually.
                           
                         
     

Important terms

*Gene pool: the collection of genes for all the traits in a population.
* Allele frequency: the percentage of a specific allele of a gene in the gene pool.
* Genetic equilibrium: allele frequencies do not change from generation to generation.
* Genetic drift: allele frequencies in a population change as a result of events or chance.
* Gene flow: the process of genes moving from one population to another.
* Immigration: the movement of individuals into a population.
* Emigration: the movement of individuals out of a population.

  
 

EOI Question

32. According to the theory of natural selection, a species that lacks the variations necessary to adapt to a changing environment will most likely -

A. become dormant
B. mutate
C. become extinct
D. fossilize

Answer the following Questions.

Head your paper Unit 6 Day 1 History of life.

1. What is speciation?
2. What does the Law of Superposition tell us about rock layers?
3. What is the main limitation of the morphological species concept?
4 . Define "morphology".
5. What is the difference between immigration and emigration?

WRITE A PAPER THAT EXPLAINS YOUR VIEWS OF WHAT EVOLUTION IS AND HOW IT WORKS. USE THE INTERNET TO DO RESEARCH.