The Earth was first considered habitable when we discovered that it was Microbial organisms that started the process. I would go with D.
Three
different ways the relatedness of species could be assessed is through:
<span>1.
</span>Their genotype. Similarity in DNA between the species is a good
indication of their relatedness.
<span>2.
</span>Their phenotype. If the two species have similar body form and function,
then there is a good possibility that they are related.
<span>The presence of intermediates, either living
or in the fossil record, can show relatedness between two species.</span>