Many experts believe that if we continue to use fossil fuels at the rate we are now, we will run out of this natural resource by the middle to end of the twenty-first century. Fossils fuels, the remains of once-living plants and animals, primarily recycle the element and when burned, these fuels add the element back into our atmosphere.

Fossils fuels primarily recycle the element carbon.

Explanation:

Fossil fuels such as oil, coal, and natural gas, are the remains of plants decomposed under anaerobic(oxygen-free)conditions. Fossil fuels take millions of years to form. When humans burn them, carbon is released into the atmosphere as carbon dioxide.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).