Exobiology, also known as astrobiology, is the branch of science that focuses on the study of life beyond Earth. It explores the possibility of life on other planets and in outer space. Option 1, which suggests that exobiology deals with the external characters of living organisms, is incorrect. While exobiology does involve studying the characteristics of organisms, it specifically focuses on those found beyond Earth. Option 2, which states that exobiology is concerned with life on the surface of the Earth, is also incorrect. Exobiology is primarily interested in life that exists in extraterrestrial environments. Similarly, option 3, which suggests that exobiology is concerned with life in the outer layers of the Earth`s atmosphere, is not accurate. The correct answer is option 4, which accurately states that exobiology deals with life in other planets and space.