Which sentence is punctuated correctly?

Question

1. Scientists know that Earth has been impacted by large asteroids in the past however; what happens if a major asteroid hits Earth now?

2. Scientists know that Earth has been impacted by large asteroids in the past, however what happens if a major asteroid hits Earth now?

3. Scientists know that Earth has been impacted by large asteroids in the past however what happens if a major asteroid hits Earth now?

4. Scientists know that Earth has been impacted by large asteroids in the past; however, what happens if a major asteroid hits Earth now?

Answer 1

The fourth sentence is punctuated correctly: "Scientists know that Earth has been impacted by large asteroids in the past; however, what happens if a major asteroid hits Earth now?"