Short answers, pulled from the story.
Louis J. Halle, Jr. published an article in Foreign Affairs magazine during 1980 that first explicitly linked space colonization to human safety against global nuclear warfare.
Toby Ord wrote about these dangers in his book titled The Precipice and identified anthropogenic risks as primary drivers for expanding into space.
The Sun will eventually expand into a red giant state approximately five billion years from now while Earth will become uninhabitable by the time this stellar evolution occurs unless humans leave the Solar System long before then.
Researchers at the University of Rochester Medical Center studied how radiation exposure affects cognitive function during interstellar travel and found that radiation levels equivalent to a mission to Mars can cause serious brain damage including cognition problems.
The Spaceguard program represents collective efforts to discover and study Near-Earth objects like asteroids and comets because these large meteoroids pose collision risks if they come close enough to Earth or strike our planet directly.