What is the easiest way to prove that the earth is more than 10000 years old? How do you prove the earth is old in the easiest way possible? If you decide to go with atom decomposition, you have to also be able to show the decomposition rate and the exponential law which describes it. I don't want to calculate its exact age, but prove it is at least as old as 10000 years. A few million years would be nice.
I don't want the historical way of proving it, I want the easiest, just as the Foucault pendulum is the easiest way to prove the earth rotates on itself, even though it was shown centuries earlier by heliocentricism, which was derived from planet trajectories. I don't think the various atom dating techniques are the best way to do it. 
I don't mind people editing my question but please keep its original meaning. 
 A: I doubt if this is a physics question, at least directly, but the physics response might be:
Look at the moon and the worn, smoothed surface craters on it, with the very slow rate of erosion of the lunar surface, these craters must have been formed a long time ago.
The moon has been in orbit around the Earth a long time, as the tidal effects have created the small grains of sand that make up the beaches. That took a while.....
We don't see very many obvious craters on Earth because of weathering processes and ocean coverage, except for comparatively rare examples, such as the well known Barringer crater in Arizona.
There are lots of other examples, but I have a feeling from your post that you may have issues with the accepted age of the Earth, so please tell me if you have any objections to the above.
A: Grandma is likely to be familiar with a map of the World, so you can explain that the continents used to be part of a single super-continent and that you can still see that from the shapes of the current continents, e.g. South America fits well into Africa. The typical rate of a few centimeters per year at which continents drift away from each other is well known but you must then build your argument around this rate. The goal is then to make plausible that it is of the order of a few centimeters per year and not many hundreds of meters per year.
We can read here:

The rate of plate movement along the San Andreas fault, 33 millimeters (1.3 inches) each year, is about how fast your fingernails grow. As a result, Los Angeles City Hall is now 2.7 meters (9 feet) closer to San Francisco than when it was built in 1924.

Now if instead of 33 millimeters per year, the movement were of the order of hundreds of meters per year, then Los Angeles would have moved tens of kilometers closer to San Fransisco and roads would buckle and would be in need of repair constantly.
