Single-celled eukaryotes arose from prokaryotes. Which organisms later evolved from single-celled eukaryotes?

Consider the classification levels of a human. eukarya ,animalia ,chordata ,mammalia ,primates, hominidae ,homo ,sapiens .which is the most specific taxonomic level in the classification system above? a sapiens b homo c hominidae d primates

In which layer do organisms on earth love?

Several billion years ago which gas was the least prevailant in the atmosphere