Final answer:
The troposphere, the lowest level of Earth's atmosphere, is where living organisms exist. It holds most of Earth's atmospheric mass and supports life because of its temperature and air density characteristics. The ozone layer and components like phytoplankton also play crucial roles.
Step-by-step explanation:
The layer of the atmosphere that contains living organisms is the troposphere. This is the lowest level of our atmosphere, extending up to 12 km above sea level and containing roughly 80% of the earth's atmosphere by mass. The characteristics of the troposphere, including its air density and temperature profile, support living organisms such as humans, animals, and trees.
Moreover, at the microscopic level, phytoplankton, photosynthetic microscopic organisms in the surface waters, capture approximately half of the energy that flows through the Earth's biosphere, contributing to the sustenance and growth of life. The ozone layer in the upper atmosphere is also essential for life on Earth as it blocks a significant amount of potentially harmful solar radiation from the sun.
Learn more about Atmosphere Layers