That Sediment Compacts Into Rock Minerals Enter Into The Bone Within The Rock And Preserve It

WE FIND THE FOSSILS WHEN MORE TIME PASSES AND THE CLIMATE CHANGES TO ONE OF EROSION. ROCK IS SWEPT AWAY, EXPOSING THE FOSSILIZED BONES.

NEXT PAGE: AN ASTEROID OR METEOR IMPACT MAY HAVE DONE IN THE DINOSAURS, THOUGH IT'S TOUGH TO PROVE THAT EVENT WAS WHAT KILLED THE DINOSAURS.

riverbanks fast enough to keep the bones from eroding. Then, slowly, minerals entered into the spaces inside the porous bones and preserved the bones as fossils.

Now all we have to do is find the rock or the sediments in which the dinosaurs were buried. But a lot of different forces have been shaping the earth before, during, and since the time when dinosaurs died. Besides erosion and deposition, earthquakes and volcanoes and the slow shifting of the plates of the earth's crust have changed the shape of the world and everything in it.

We know, for example, that dinosaurs lived in Indiana. But if you poke around the dirt in Indiana, you're digging in sediments that are 300 million years old (except for surface glacial debris that is much younger than dinosaurs). That's a lot older than the oldest dinosaurs.

But in eastern Montana, sediment of the right age happens to be exposed. So we can walk around out there and literally walk on the ground that the last dinosaurs lived on. However, chunks of this dinosaur time are missing. Each of the striped bands in the hillsides of these badlands represents a different time or weather condition when sediment was deposited. A break could mark a time when nothing was deposited, a time when the environment had shifted to one in which ground stopped building up or even started eroding. We have no way of knowing how long these gaps were, how much time was swept away by erosion.

Or the stripes in the rock could come from continuous sediment buildup that changed in form—from stone made from silt to stone made from sand, marking times when flooding brought in coarser sand grains to the site.

Nowadays, eastern Montana is not depositing anything. It is eroding, fast. The environment is dry and windy, with huge seasonal temperature shifts. Gusting winds, and seasonal freezing and thawing, crumble rock quickly. This extreme weather has been around for only a few thousand years, but it has turned this part

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