How can it be possible that scientists do not currently have fossil evidence for every organism that once lived?

How can you know what happened millions of years ago if no one was there to see it? Evidence and observation are the building blocks of all scientific inquiry; ... of the fossil record, geological formations, and genetics attest to change having taken ... clues together into a cohesive explanation of the diversity of living things. Because of the specialized and rare conditions required for a biological structure to fossilize, many important species or groups may never leave fossils at all. Even if they do leave fossils, humans may never find them—for example, if they are buried under hundreds of feet of ice in Antarctica.

Explanation:

it is very expensive

explanation:

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.