Please choose the correct answer to the question: Scientists study the current conditions of many solar system objects to gain insight into conditions early in the history of Earth. Which phenomenon most closely models current theories of early Earth?

Answer1: liquid forming valleys on Mars Answer2: hundreds of active volcanoes on Io Answer3: rock and ice forming the core of Neptune Answer4: ice covering the entire surface of Europa

Answer format: answer1/answer2/answer3/answer4