One method I know of is comparing a sample of the rock to other samples which the scientist already knows the age of. I forgot what this method is called but I know it's used by lazy scientists that use other scientist findings like the age of a rock to compare to their own work
4. Gene Pool is not a mechanism, thus your answer!
Answer:
It effects the body by causing symptoms like muscle aches, low-grade fever, headaches, sometimes rashes, swelling of the lymph glands may also occur, and flu-like illness. These are symptoms after a few weeks of being infected.