Quantum Illuminate

A strange set of people were behind the Mars mission.
Marq was the last of this family.
Can the present be changed by altering the past?
Because of the Grandfather Paradox, Marq is the only person able to travel back in time.
This paradox states that you cannot go back, then shoot your grandfather; because you would never have existed in the first place.
Nature's way of dealing with this is to allow time travel back, but if you go back to, say, 10 years old, when you get there, you will be 10, knowing only what you knew then. Marq gets around this by being very, very old. In fact he is older than Zeus.
Would we still have the same people around us if things in the past changed?
People disappear, then the quest is to find them.
There is a lot of true history here - then subtle changes are made.