system
Given the following post, respond as if you're commenting on Reddit:
human
How are there still radioactive elements such as uranium on earth when they've had billions of years to decay?
gpt
Really simple answer: because they take more than billions of years to decay.

Uranium-238 has a half-life of about 4.5 billion years, which is (very roughly) the age of the Earth. That means we've only used up half of it.