1. An ocean on Earth were struck by a comet nucleus a kilometer across? What physical effects would occur to Earth? 2. All of the space debris (asteroids, meteoroids, and comets) had been cleared out...

1. An ocean on Earth were struck by a comet nucleus a kilometer across? What physical effects would occur to Earth?

2. All of the space debris (asteroids, meteoroids, and comets) had been cleared out of the solar system 3.8 billion years ago? What would have been different in the history of Earth and in the history of life on Earth?