Tuesday, May 06, 2008

Making up stories

I was with environmental science students in the campus woods the other day. Big pink granite boulders. The bedrock under the boulders is a green volcanic rock. Where did the boulders come from?

Pretend it is 1840. Two stories explain the granite boulders.

--During the great flood of Noah, when the Earth was covered with water, rock-bearing ice bergs drifted south from the Arctic. As they melted, they dropped their burden. The story nicely accounts for why we don't find these "erratic" boulders much further south.

--At some time in the past, the Earth's climate was colder and large parts of the northern continents were covered with ice. The glaciers moved out from their centers of accumulation, eroding the crust of the Earth, and plucking boulders from the downstream slopes of hills. As the climate warmed and the ice melted, its burden of rock was dropped in place.

Two stories. Both propose an improbable event: an all-engulfing flood, a continent-spanning sheet of ice. Which to believe?

Continent-spanning glaciers exist today, in Greenland and Antarctica. Water for glaciers of greater extent could come from the oceans.

The water for an all-engulfing flood requires a miracle.

The ice theory makes predictions, based on what we see where glaciers exist today. The bedrock should be scratched, and the scratches should all be aligned in the same direction, pointing to the centers of ice accumulation. Here on the Stonehill campus, if we follow the scratches north, we should find a source for the pink granite boulders on the south-facing slope of a hill. In fact, all of the ledges we find on the campus should be on south-facing slopes, and every rock we find should have a source somewhere to the north. And so we go, tramping through the woods, and -- lo and behold -- our predictions are confirmed in every respect.

This is the game of science. Explain the past using only natural agencies that we see at work in the world today. Find the simplest story that explains all of our observations. Be happy when we can find a story that can be as easily falsified as confirmed.

And, on a lovely bright spring day, let the students figure it out for themselves, by placing them in front of the evidence and letting them ask -- and answer -- questions.