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The weathering of rocks by chemicals is called chemical weathering. Sometimes rainwater is naturally acidic because it contains carbon dioxide. This is caused when fossil fuels such as coal,oil and natural gas are burned, carbon dioxide escape into the worlds atmosphere.

nucleic acid molecules are incredibly complex, containing the code that guarantees the four different nucleotide units comprise dna, the nucleic acid of interest to the genealogist. and one of four nitrogen-containing molecules called nucleotides