For perhaps the third time in the four-and-a-half-billion-year history of the planet Earth, the world is a blank slate on a global scale.

Mountains have pushed up among the huge inland swamps and seas, the nights are cooler than the days, and it is actually colder (though not markedly so) in Siberia and Canada than it is close to the equator. These kinds of seasons have never existed on the planet before.

In the oceans, entire families of molluscs, plankton, and reef builders that had formed the basis of a 200-million-year-old ecosystem are extinct.

On land, the gigantic dinosaurs are gone, all the flying and swimming reptiles are no more, and the huge tree ferns and cycads that formed the tropical ecosystem of most of the Earth have largely disappeared. It is possible that the planet is recovering from an asteroid impact just seven million years earlier.

The stage is cleared for the evolution of the world as we know it, but it won't happen overnight. Instead, enter the world as it was 60 million years ago. Journey to the marshes, lakes, and rivers of what we now know as North Dakota.

Fossils from Wannagan Creek help us understand more about the world of 60 million years ago.

Look at the Geologic Time Scale for a brief overview of the history of the earth.

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