In my oppinion we all are immortal.
Everything is made out of small small particles. The particles creates cells that joined together creates a human brain. These particles will live forever. Because of this every human brain consists of a little part of some other brains from way back in history. When one person dies and are buried in the soil on one place on the earth, the soil takes the particles from the corpse and creates food for the remaining living beings on that place. These living beings often becomes food for OTHER living beings, often humans since we are positiones quite high on the food chain.
Thus if some particles manages to stick together as a cell, and if this cell contains some memory, every human can remember some parts of history as if they themself had been there to witness it. And in fact, they have. This of course includes memories from animals as well
The fact that we only use about 20 percent of our braincapacity may be the reason why we dont know about these memories. If we could use the absolute max of our brains i am sure that the humans are of a single mind with about the same memories and thoughts. The reason why our thoughts are so different is just a result from the fact that we use different 20 percent of our brains. As time goes by we will become more and more of a single mind until, some time in the future, we are.
Well thats about it. Summary: We are all immortals, we all are connected(and that includes EVERYTHING on earth), and nothing that we may do are going to change this fact. If someone are positively sure that i am wrong, that the small small particles can NOT hold memories, if together, for a very long time and so on, please feel free to enlighten me. Until then i will live my life to the fullest and do as i please, because i am truly immortal.