Here's why:

* Closed System: A closed system exchanges energy with its surroundings but not matter.

* Earth's Matter: While the Earth receives energy from the sun (radiation) and loses energy to space (infrared radiation), it doesn't gain or lose significant amounts of matter. The same atoms and molecules that are on Earth today have been here for billions of years, constantly cycling through different forms.

However, it's important to note:

* Minor Matter Exchange: The Earth does experience extremely small amounts of matter exchange with space. For example, meteorites fall to Earth, and some particles from the atmosphere escape into space.

* Human Impact: Human activities, such as launching satellites, can also result in a very small amount of matter leaving the Earth.

* Open System for Energy: While closed for matter, the Earth is an open system for energy. The planet constantly receives energy from the sun and loses energy to space.

So, while the Earth is essentially a closed system for matter, it's not entirely "closed" due to these minor exceptions.