If an element has a half-life of twenty million years and there is 30% remaining in the rock, how old is the rock?

1. why does the same side of the moon always face earthc.the rotational period of the moon is equal to one revolution around earth2. which is greater the moons period of rotation or its period of revolution  b.the moons revolution period around earth3.what was the major accomplishment of the apollo missions  c.sending the first human into space4. which of these space missions involved the deployment of lunar roversa. voyager 15. which scientists are going to explore next on kepler-186fd. evidence of existence of life6.which mission is not going to explore the outside of the solar  systemb.safir7.which technology limit the future of space explorationb. scientist must first develop certain technologies before missions can be completed.

The law of conservation of mass states that a mass of an object or the amount of matter composed inside an object or thing will not change unless it is added or removed of the matter that is contained in the object itself.