Which of the following statements best explains why the scientific search for extraterrestrial life generally focuses on looking for life that is at least somewhat like life on Earth?
1: Extraterrestrial life is likely to be completely different from Earth's life.
2: Earth-like conditions are rare in the universe.
3: Earth's life forms are the only ones that can survive in space.
4: It is easier to study life forms similar to those on Earth.