CRATERS!
We talked about dinosaurs and discussed one of the reasons why we think they became extinct: Possibly hit by showers of asteroids.
We placed mini dinosaurs on the sand and then dropped various sized balls from a height into the tin of sand. Each ball created a crater in the sand when dropped. We found out that small marbles create a small crater and large ball creates a much bigger crater.
We saw the imprint of the balls in the sand.