  The study of planets outside our solar system may lead to major advances in
our understanding of the Earth, and provide insight into the universal set of
rules by which planets form and evolve. To achieve these goals requires
applying geoscience's wealth of Earth observations to fill in the blanks left
by the necessarily minimalist exoplanetary observations. In turn, Earth's many
one-offs, e.g., plate tectonics, surface liquid water, a large moon, and life -
which have long presented chicken and egg type conundrums for geoscientists -
may find resolution in the study of exoplanets possessing only a subset of
these phenomena.
