Time Shark

            Pop!  Three men and a woman appear in the water in the middle of the ocean, all wearing fancy wetsuits with shiny light-up panels.  They discuss how they guess they have come back too far, and laugh a bit until they realize that they are being circled by a shark with a bone ridged fin.  The woman takes a few pictures using a camera built into her suit, but then the shark turns to attack the group.  They briefly mess with matching bracelets that they all wear, and with a pop they disappear.

            In the present, the group appears on the beach at an island research facility.  We learn that they are temporal archivists who are mapping the past, and that they believed this island might be the geographical point where life began.  They go out into the water to place chrono-tracking devices and all is going well when suddenly one of the men is eaten by an enormous shark.  Another of the men lays chase to the shark to get revenge but suddenly the shark disappears.  The time jump bracelet in its stomach is auto-skipping back through time.

            Now the remaining three archivists must chase the time shark into the past, using the resources of each regressive era to hunt the beast.  The potential crisis:  If the shark continues to skip back through time, it could feasibly eat the creature that first crawled out of the sea, and thus end life on Earth as we know it.  As they fail to capture the creature in each century, the archivists come up with one last ditch effort.  If they can find a way to pit the time shark against its own distant ancestor, maybe they can effectively erase it from existence and save mankind.