Final answer:
The ozone layer, which is located in the stratosphere and composed of ozone (O3), fulfills the functions of regulating temperature, blocking UV rays, and containing oxygen among the Earth's atmospheric layers.
Step-by-step explanation:
The option that regulates temperature, blocks UV rays, and contains oxygen is the ozone layer. The ozone layer is a critical part of the Earth's atmosphere, located in the stratosphere. It is composed of ozone (O3), a heavy form of oxygen with three atoms per molecule, and it serves to absorb ultraviolet light from the sun, protecting living organisms from harmful UV radiation, which can cause skin cancer and genetic damage. Due to its ability to block UV rays and its location in the atmosphere, where it contributes to heat regulation, it performs the functions that the question describes. The other options listed do not perform all these roles: the atmosphere is too broad a term and includes many layers with various functions, the Earth's core is not related to the atmosphere and has no role in blocking UV rays or containing oxygen, and the troposphere is the lowest part of the atmosphere where weather occurs but is not primarily responsible for blocking UV rays.