Final answer:
The formation of iron in the core of a massive star results in a Type I supernova by causing the star to contract, generate shock waves, and eventually explode. This explosion produces elements heavier than iron, leading to the dispersal of these elements into space.
Step-by-step explanation:
When a massive star's core is primarily composed of iron-nickel metal, fusion reactions involving iron require energy instead of releasing it. This lack of outward pressure from fusion reactions causes the star to contract under the force of gravity, which heats the core and generates expanding shock waves within the star. The combination of the core's high density and temperature, along with the shock waves, leads to a rapid collapse and explosion, resulting in a Type I supernova. During this explosion, elements heavier than iron are produced, and both these elements and the remnants of the star are ejected into space.