Definition of global warming

How do you date a sample of rock that you suspect as being one of the earliest on earth

What type of plant is good for a bioassay and where can i buy it? i only have a month.

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.