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?

What is the correct answer to the question from the following choices?
Pick from:
+ liquid forming valleys on Mars.
+ hundreds of active volcanoes on Io.
+ rock and ice forming the core of Neptune.
+ ice covering the entire surface of Europa.
hundreds of active volcanoes on Io