What is the envelope of gases surrounding the Earth called?

The envelope of gases surrounding the Earth is called the atmosphere. This layer of gases is essential for maintaining life on our planet as it provides the necessary oxygen for respiration and helps regulate temperatures through the greenhouse effect. The atmosphere is composed primarily of nitrogen (about 78%) and oxygen (about 21%), with trace amounts of other gases, including carbon dioxide and argon.

Different layers exist within the atmosphere, such as the troposphere, stratosphere, and others, but collectively, they all form what is referred to as the atmosphere. This layer plays a crucial role in weather patterns, climate, and protecting living organisms from harmful solar radiation.

The other options refer to different concepts: the hydrosphere encompasses all water bodies on Earth, while the stratosphere and exosphere are specific layers within the atmosphere, not the entirety of the gas envelope itself.