Why did the world's climate change?

The appearance of living things changed the Earth's atmosphere, providing the conditions for climate change. The first living things were plant-like creatures. They used the sun's energy to change carbon dioxide and water into sugars, which they used for food, and oxygen, which they released into the atmosphere. Some of this oxygen turned into ozone, forming the layer that now protects us from the sun's ultraviolet radiation.

In more recent times, geologists and paleontologists have been able to make more accurate measurements of the age of ancient rocks. Trees produce a new 'ring' every year, and these can be measured and counted. The width of the ring shows how well the tree grew in any year, reflecting climatic conditions at that time. The rings of even partly fossilized trees buried in bogs can be measured, and these measurements provide accurate records of climate changes over the past 750,000 years. By measuring the radioactivity of once living material, scientists can make accurate measurements up to 40,000 years ago.