We think that an increase in the length of the dry season sometime after 27 million years ago caused the loss of those plant groups on the Ethiopian Plateau.

The loss of Daniel Pearl ... reminded us of how valuable a free press is, and it reminded us that there are those who would go to any length in order to silence journalists around the world.

However, he added: "This is highly sensitive to small changes in the proportionate loss rate because the amount of assets is so big and the length of time that the assets are covered."