The ancient Egyptians had a conception of zero, and used a herioglypical symbol for zero. China had a counting rod system, with an empty space being a zero and Mathematical Treatise in Nine Sections had a round symbol being used for zero. Other authors were familiar with the concept of negative numbers.
These are alll before Indian "invention" (probably be discovery) of zero.
Lets say you are a hunter gatherer, you hunted a pig in the forest. You and your fellow cave mates had a good meal. Another cave mate arrives an hour later. Asks how many pigs you hunted, your reply 1, asks how much is left, given you had everything, and nothing is left, what answer would you give?
Congratulations you just invented zero in 100000 BC.
What you are defining is zero as quantity. Thats not that difficult. What is brilliant is zero as a place holder which practically made counting to big numbers a breeze.
