A biome is a large naturally occurring community of flora (plants) and fauna (animals) occupying a major habitat (home or environment).

The crust is the Earth's outermost layer and is divided into oceanic and continental types. Oceanic crust is 3 miles (5 km) to 6 miles (10 km) thick and is composed primarily of denser rock. Continental crust is 20 to 30 miles (30 to 50 km) thick and composed primarily of less dense rock. The crust makes up approximately one percent of the Earth's total volume.

In contrast to the solid terrestrial planets, the outer planets (Jupiter, Saturn, Uranus, and Neptune) consist of hydrogen and helium gas and water.

Like decomposers, scavengers also break down the dead bodies of plants and animals into simple nutrients. The difference is that scavengers operate on much larger refuse and dead animals (carrion). Decomposers then consume the much smaller particles left over by the scavengers.

The four planets closest to the Sun (Mercury, Venus, Earth, and Mars) are called terrestrial (Earth-like) planets because, like the Earth, they're solid with inner metal cores covered by rocky surfaces.