Why can we find gold, platinum and other heavy elements on Earth?

We know they exist and we know that their value is very high: gold and platinum are probably two of the most well-know metals, especially for their money value, and we know they're not so common too. All right, but... where do they come from? How they are created? This are 2 questions that aren't made often, but it's interesting to comprehend.

Easy.. they come from the Universe: you never must not to forget where we live. Yes obviously, on Earth, but, more precisely, in the Universe. In the Universe something strange always happens: a black hole could "eat" a star, stars that never had a nuclear fusion, "life-nominated" planets hundreds of light-years far, great explosions and much more.

...yes, so?

So, we start from stars: a star evolves. It "borns", "lives" and , as all, "dies". How does it "die"? A star burns hydrogen, commuting it in Helium for the 90% of its life. This nuclear reaction "products" energy, that allows life at the right distance from the star. But what happens when hydrogen ends?

A star "lives" in a hydrostatic equilibrium, balancing the nuclear-reaction pressure and its gravity. When hydrogen ends, there is no more pressure coming from the reaction (hydrogen ends--reaction ends), so gravity is major and the star gets smaller. But a star is full of gas (helium, do you remember?), and when you compress a gas, it warms up. When the temperature rise enough, until 100 millions K, the nuclear-reactions stars again, burning Helium, if the mass of the star is great enough to support this 

Normally, in greater-mass stars, the reaction continues burning the gas has been produced before: Hydrogen to Helium.. to Carbon...to Nitrogen... to Neon....to Oxygen.... increasingly heavy metals. And which are these heavy metals? Yes, right!! From Oxygen to... Silicon... to IRON!! Here's the point

When a star reaches to IRON, nuclear-fusion-process is not more exothermic, but ENDOTHERMIC. It needs energy to process again! At this point, nuclear-fusion-pressure can no more contrast the gravity, that "crush" the mass of the star until it bursts!!

During this process, neutrons collide themselves generating heavy metals like gold, silver, platinum, copper,lead and even zirconium

The explosion releases in the Universe approximately the 70% of star mass, containing the metals (in the form of gas) that "travel" through the Universe hitting some nebulas, which other stars born it. 

This is why we can find this metals on Earth