Rebecca Morelle.  Science Correspondent, BBC News

The Anthropocene - a new geological time period that marks the "Age of man" - began in 1610, a study suggests.
Scientists believe that the arrival of Europeans in the Americas had an unprecedented impact on the planet, marking the dawn of this new epoch.
The findings are published in the journal Nature.
Others say that the industrial revolution or the first nuclear tests better signal the start of the Anthropocene.
While some believe the exact date for a new epoch can only be determined with the benefit of thousands or even millions of years of hindsight.
An international Anthropocene Working Group is currently reviewing the evidence and will announce its favoured start date next year. Read full story