Transcript: In the most massive evolved stars, the star has an onion skin layering where heavier and heavier elements are concentrated in layers closer and closer to the core because the temperature and pressure continue to increase moving towards the center of the star. For example, in a fifteen solar mass star the outermost layers will be filled with a cosmic mixture of three-quarters hydrogen, one-quarter helium by mass. The inner four solar masses will be helium at a temperature of about 60 million Kelvin. Inside that is a layer of carbon at 200 million Kelvin. The inner two solar masses will be oxygen and silicon, successively at a temperature of about a billion Kelvin, and at the center is one solar mass of iron at a temperature of 6 billion Kelvin. Not only is there a layering but there’s also a speed involved in the timescale of producing heavy elements. Heavier and heavier elements are produced on faster and faster timescales late in the star’s life.