What is some evidence that makes plate tectonics is such a firmly believed idea?

Some life "rode" on diverging plates, became isolated, and evolved into new species.

Explanation:

your answer is "the 1950's"

the diploid number of chromosomes is sometimes represented by the symbol 2n. for the fruit fly, the diploid number is 8, which can be written as 2n = 8, where n represents twice the number of chromosomes in a sperm or egg cell.