Feathers are an apomorphy for birds. Many plants are aquatic, including seaweeds . Many animals are arboreal, including the sugar glider. An arid area is dry and hot, with little rainfall and few plants. An asteroid is a large rock or small planet orbiting the Sun.
Most asteroids lie in a belt between Mars and Jupiter .
An asteroid impact with the Earth may have caused the K-T mass extinction. The atmosphere is the mixture of gases that surrounds the Earth. The Earth's atmosphere is mostly nitrogen. Everything is made up of tiny atoms. An atom is the smallest part of an element that has the properties of that element.