Here are some examples:
* Atmosphere: The layer of gases surrounding the Earth.
* Biosphere: The part of Earth where life exists.
* Hydrosphere: All the water on Earth.
* Lithosphere: The Earth's rigid outer layer.
The prefix "sphere" can also be used to indicate a specific area of activity or interest:
* Sphere of influence: An area where a person or group has power or influence.
* Sphere of knowledge: A particular area of expertise or study.
Therefore, "sphere" is a prefix that signifies roundness, a specific area, or a domain of activity.