What gas important to life was absent from earths earliet atmosphere a methane b. nitrogen c. oxygen d. carbon dioxide

What are four key elements of the study of economics?

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area

Which of the following determines the specificity of a dna probe? a. type of radiation b. level of enzymatic activity c. number of neutrons d. complementary base pairing