Final answer:
Astronomers hypothesize that around 2 million years ago, significant damage to the Earth's ozone layer led to increased ultraviolet radiation, possibly due to extraterrestrial influence. However, the modern degradation has been caused by chlorofluorocarbons and other human-made chemicals, leading to the ozone hole over Antarctica.
Step-by-step explanation:
Approximately 2 million years ago, the Earth's ozone layer may have experienced significant damage, leading to an increase in ultraviolet radiation reaching the surface. This could have caused extensive harm to life on Earth as the ozone layer is crucial for blocking a substantial amount of harmful solar radiation. The cause of this ancient damage to the ozone layer remains speculative but may have involved extraterrestrial events or natural atmospheric changes. It's important to note, however, that more recent depletion of the ozone has been directly linked to human-made chemicals such as chlorofluorocarbons (CFCs), which have had a measurable negative impact on the ozone layer.
In the modern context, the discovery of an ozone hole over Antarctica in the 1980s highlighted the vulnerability of the ozone layer to human activities. Substances that release chlorine and bromine gases, found in aerosols, coolants, and other products, were identified as chief culprits in ozone depletion. Fortunately, global actions like the Montreal Protocol have helped in reducing the use of these substances, leading to a slowdown in the rate of ozone loss. The recovery of the ozone layer is an ongoing process critical to protecting life on Earth from harmful UV radiation.