Troposphere
The troposphere starts at the Earth's surface and extends 8 to 14.5 kilometers high (5 to 9 miles). This part of the atmosphere is the most dense. Almost all weather is in this region.
Sources
NASA, 2013. Earth's Atmospheric Layers. https://www.nasa.gov/mission_pages/sunearth/science/atmosphere-layers2…. Accessed 30 June 2021.