You would find plants and animals in the troposphere. This is the lowest layer of the atmosphere, extending from the Earth's surface up to about 7-17 kilometers (4-11 miles) high. It's where all weather occurs, and it contains the air we breathe, along with most of the atmosphere's mass.

While some organisms can survive in the stratosphere (the layer above the troposphere), they are primarily microscopic and not the kinds of plants and animals we typically think of.