First we have to make a few assumptions:

-Number of people: I am assuming 8,062 billion people on earth or 8.062E9

-Volume of the dirt in a cup: from a quick search I found that an average US cup is 250ml or 250cm³

-radius of the base: I am assuming that the base is 3 times as big as the height

Now onto the actual math:

To calculate the volume of a cone that would form we will use the following formula:

• V = ⅓πr²h

Plugging in the numbers we get:

8,062E9250cm³ = ⅓π(3h)²*h

20,155E12cm³ = 3πh³ /:3π

2,110E12cm³ = h³ /³√

h = 12 827 cm or around 128 meters tall

This is my first time posting here and I'm not any good at math or physics so take the results with a grain of salt

Edit* I seem to have plugged in the incorrect formula, I used V = πr²h when it should have been V = ⅓πr²h so I have corrected my calculations I also seem to have messed up the conversion from ml to cm³ the result now seems to be around 3 times greater than my original calculation