* Natural Abundance: Some elements are naturally occurring but incredibly rare. Finding them in nature is extremely difficult.
* Artificial Production: Many elements are not found naturally because they are radioactive and have very short half-lives. These elements are only created in laboratories.
Generally, we can say:
* About 90 elements are found naturally on Earth. These include everything from hydrogen and oxygen to gold and uranium.
* The remaining elements (around 20) are synthesized in laboratories. These are often referred to as "synthetic elements" or "transuranic elements" because they are heavier than uranium.
So, while a precise number is difficult, there are approximately 20 elements that are not found naturally on Earth.
