Genetic engineering occurs when

scientists make an exact copy of an organism
scientists remove genes from a cell to study them
scientists turn genes on and off in order to change a characteristic
scientists make two animals mate in order to produce offspring with desired traits

Which statements explains what the fossil records indicates? check all that apply. a) earth is 4.5 billion years old b) many organisms have become extinct c) mammals have always existed on earth d) mass extinctions have occurred several times on earth e) the amount of water on earth has decreased over time?