Exobiology, also known as astrobiology, is a field of science that focuses on the study of life beyond Earth. It aims to understand the origin, evolution, and distribution of life in the universe. Option 1, extinct forms, is not the correct answer because exobiology specifically deals with living organisms and their potential existence outside of Earth. Option 2, life in other planets, is similar to the correct answer but does not encompass the broader concept of life in the universe. Option 4, life in marine habitat, is not directly related to exobiology as it specifically focuses on life forms in Earth`s oceans. Therefore, option 3, life in outer space, is the correct answer because it encapsulates the study of life beyond Earth`s atmosphere and planetary boundaries.