What wiped out 90% of living coral in the 1970’s

Which of the follow describes a disadvantage secondary sources have compared to primary sources?

Ascientist wanted to formulate a pill to attack a specific type of bacteria that infects the throat. which biological component would be best to use as a model for the pill's function? bacteriocytes phagocytes complement antibodies

What is any method of measuring the age of an object or event in years, such as using atomic half-life?