List the four stages of the policy life cycle, and show how the discovery of ozone layer destruction and the subsequent responses to it illustrate the cycle.

The stages of a policy life cycle typically include 1) Problem Identification, 2) Policy Formulation , 3) Policy Implementation and 4) Policy Evaluation.

Now, using the issue of ozone layer degradation, these stages can be identified as follows: \n\n1) Problem identification: The ozone layer destruction was first noticed and reported by scientists. The steady decline in the amount of ozone in Earth's stratosphere (aka 'the ozone hole') was identified as a significant environmental issue. \n\n2) Policy formulation: Responding to the discovered problem, international policies and legislation were formulated to protect the ozone layer. Most notable of these was the Montreal Protocol, which sought to reduce the production and consumption of substances responsible for ozone depletion. \n\n3) Policy implementation: After the formulation of the Montreal Protocol, countries all over the world began implementing it by limiting the use and production of chemicals that harm the ozone layer, such as chlorofluorocarbons (CFCs). \n\n4) Policy evaluation: Researchers and scientists periodically assess the state of the ozone layer to determine the effectiveness of the implemented policies and whether additional measures are needed. Ongoing monitoring suggests that the ozone layer is recovering, demonstrating that policies implemented under the Montreal Protocol have been effective.

In summary, the issue of ozone layer depletion clearly demonstrates the stages involved in the policy life cycle. Identification, formulation, implementation and evaluation are all followed in systematic order. This example, therefore, stands as a testament to the importance of the policy cycle in identifying, addressing and strategizing solutions for serious environmental problems.