The world would be unrecognizable.
I was first brought to this by a single answer, but there are a lot of answers that fail to recognize just how much a LITTLE change that far back would make for today, or even a hundred years after you moved the rock.
Let’s ignore, for the moment, that you actually touched the rock, and could have left genetic material or even some virus or bacteria on it. Let’s even ignore that you were there, and were somehow able to move the rock without being physically present.
The rock may have caused a creature that would have been unobstructed to now take a different course, or maybe they can now go straight since the rock isn’t in their way anymore. Now, every creature that they would have interacted with, or that they interact with which they wouldn’t have before, now have their own paths changed.
These changes will move outward at least at the speed of the fastest animal, but could be up to the speed of light in some instances (a prey animal seeing a predator that it wouldn’t have noticed before, and moving from the area).
As this expanding circle grows, any creature conceived after that moment is probably a creature that wouldn’t have been conceived before. In a hundred years, entire herds would be in different areas, populated with individuals which wouldn’t have existed in the original timeline.
By modern day, there’s a good chance that humans wouldn’t exist, having been supplanted by whatever other species became dominant. Maybe there never was an intelligent species at that point.
To explain this in simpler terms… If I wanted to go back in time and remove a person from existence, going back and killing your father is the lazy solution (as well as being far too visible to any ‘time police’ out there). If I wanted to be subtle about ending your existence, I would just go back to the day of your conception and play the radio loudly.
What will that do? Well, if your father enjoys music, he may sway his hips along with it. This mixes up his internal juices just enough that a different sperm will win the race later that day. Thus, you’re never born. Instead, a possible brother/sister is born in your place.
Now, extrapolate that same situation over a billion years of animals tripping over that dang rock, and you’ll realize just how dangerous time travel could be.
I’m going to be a contrarian here, but for a subtle reason. Picking up and moving the rock won’t do much. But leaving behind bacteria, skin cells, and viruses from your hand, along with whatever you tracked in on your feet… that might make a huge difference.
A billion years ago, no modern animals and plants existed, just bacteria. So what you left behind — if it had a chance to reproduce and spread — might change the future in a drastic and unpredictable way.
So the time period is Proterozoic and you take great care that your only effect on the world is to move a single rock.
There are two ways of answering your question.
First, within a timeline, would a minor change have big ramifications? No, only the potential for big ramifications. You could also make a major change and have the potential for zero long term ramifications.
The butterfly effect addresses the compounding/cascading series of events from initial conditions where a small change could have large effects in chaos theory.
Second, what is the nature and effect of changing something in the past.
Let’s consider a single predestined timeline where you are powerless to have an effect.
When you go back 1 billion years and make a change (large or small) it will have absolutely no effect on the world you know. Whatever you do already happened to create the world as you know it. You going back in time was a part of that world already.
Next let’s consider a split time line.
This time (bah dum tss), you go back and the moment you emerge onto the scene 1 billion years ago, you splinter time. There’s the original version you know where your time travel never happened, and the new version you created where it did.
This has two possible outcomes when you return.
- Your machine returns you to your own “Original Present” timeline (no changes whatsoever) at the moment you left. One could go a step further that this is now an altered timeline where you exist with knowledge of the world 1 billion years ago vs the pristine original you that never went back in time.
- You are sent into the altered timeline of the “New Present”. Depending on your thoughts, you may say that #2 is the only possibility because #1 has now been destroyed by your meddling.
#2 presents a problem where a version of you may already exist in the altered timeline. Perhaps you become that person with no memory of your previous self, perhaps you replace that person and retain your identity, or maybe (more likely) you both exist.
Last model, everything everywhere with every possibility of everything you could have done already exists.
Billions of realities every moment containing every potential outcome for every potential action. In this final scenario, your time machine allows you to travel and visit any of these timelines and tour trillions of different consequences to your rock relocation.
