Scientists found stone tool specimens in a cave in africa. using potassium–argon radiometric dating, they discovered that the tools contained 25 percent radioactive potassium-40. how old are the tools? (you must show your calculations to receive credit.) *the half-life for potassium-40 to argon-40 is 1.25 billion years.

The organelle pictured is found in cells of and is theorized to have once been an independent organism.

What were the main components of earth’s earliest atmosphere? oxygen and ammonia hydrogen and helium oxygen and nitrogen hydrogen and nitrogen

Study the picture of the ocean. which is the best example of an organism’s niche shown in the picture? a. the environment contains several of the same species of coral. b. the shallow area of the ocean meets the needs of the coral and the fish. c. the ocean has fish and coral that live in the same area. d. the coral take in food from the water and provide shelter for the fish.