Researchers in Florida and Washington have published research in that suggests a new theory on the extinction of the dinosaurs, putting it down to space dust in the earth's atmosphere and changes in the planet's orbit. Experiments in space have shown that the Earth picks up about 30,000 tonnes of space dust a year. They did calculations spanning 1.2 million years to prove that the amount of dust drifting about in space can vary in a 100,000 year cycle. This dust, they argued could alter climate. Changes in Earth's orbit, causing it to move closer or further away from the sun can also cause small changes in climate. This effect could be accentuated when cooler periods overlapped increased dust levels, and together they could have caused sufficient change to have started a gradual extinction of dinosaurs which in turn reached a final and definitive conclusion with an asteroid or cometary impact.