Encompass our life experiences. These types of memories often have an emotional component. As such, the role of adrenalin has been investigated to this end.
If the hormone is present in the bloodstream during a highlgy emotional event, then it might enhance the encoding of the event.
If adrenalin is released in high amounts during a learning experience, the result can be very helpful. For example, if the emotion is fear-based, and rational, then this can be very helpful (i.e. in times of danger).
However, it can also be very problematic as is the case for individuals with PTSD. For these people, when adrenalin is released, it often activates Flash Bulb Memories.