1. Because it is.<quoted text>
1. Then why do they describe it as accepted by the majority of the scientific community?
2. Fact: In science, an observation that has been repeatedly confirmed and for all practical purposes is accepted as “true”.
2a. Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts.
3. Ya right. Here's an awesome guess:
"Life on Earth evolved from a universal common ancestor approximately 3.8 billion years ago."
2. Repeating what I said still makes your original post wrong.
3. Not a guess, it's what the evidence demonstrates.