other for pollutants

Some known problems cannot be addressed by humans on Earth, and include:

• The eventual exhaustion of hydrogen in the Sun and the star's transformation.
• A sudden appearance of a black hole that could consume our planet.
• A burst of gamma rays from a close supernova tha...

• The first refrigerators contained flammable, toxic, and highly reactive liquids and gasses.
• Most refrigerators use hydrofluorocarbons (HFCs), which are safer than Chlorofluorocarbons (CFCs). CFCs are known to be harmful to the ozone layer.
• Refrigerators should be set at a ...

Most natural UV light comes from the sun. Only 10 % of sunlight is UV, and only one-third of it gets through the atmosphere.

Of the solar UV energy that reaches the equator, 95% is UVA, and 5% is UVB. No measurable UVC from the sun gets to the Earth's surf...