Why are lichens so important for primary succession?

Are the earth's ocean floor and continents the same age geologically? why or why not?

Which of these substances does not protect against invaders in the nonspecific immune response? a. saliva b. mucus c. tears d. urine

Aragonite shells of clams, snails, or scleractinian corals may be preserved unaltered in cenozoic deposits, but they are generally dissolved or recrystallized in older deposits. true or false