If I Die A Death

The earth,after its existence has seen millions of centuries.Species that were present before our birth and many generations that will come.From the extinction of species like dinosaurs to the modern human race everyone has to taste death.
but problem is that no one knows why?
what is death and what happens afterwards.
different religions and believes have explained this phenomena in their ways but the problem is which one to believe.
what if we are just an experiment placed in a situation to see how we perform?
To see the abilities how we survive?
what if life don't end after death?
what if we have to see another place and another place like earth after death?
No one knows!