I don't know how a red giant star comes along.
All stars begin as being made up almost entirely of hydrogen.
Eventually, all of the hydrogen in the star's core is converted to helium and nuclear reactions stop there, while outside the core the reactions continue. The contraction supplies energy to the core, which then gets hot- ter than ever. This causes the outer layers to get hotter too, and to expand enormously. Our oceans will boil away, and everything on Earth will be burned to a crisp. Ph. D., Division Director.