Describe how the 20 amino acids are similar yet different in their structure

They are different in structure because of their side groups because this is what makes each of the amino acids in our body, which will point out their own difference towards one another. Their similarities and what they have in common is they all have chemical structures in their amino acid molecules.

relative dating involves things like higher layers are most recent than rocks lower in the sequence. this can be extended to the known sequence of fossils. rocks containing rabbit fossils are later than those containing dinosaur fossils.  

absolute dating methods mainly use radioactive elements that have known rates of decay and produce recognizable products. for example potassium 40 decays to produce argon. once a rock has solidified the argon is trapped. by measuring the argon and potassium0 you can get an accurate number for the age.  

some other methods are good for archaeological ages. dendrochronology involves recognizing the sequence of tree rings. the orientation of magnetized particles in baked clay can be used to date a fire.

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d. planting trees

the trees take in carbon to make oxygen.