“If you put dirt into water, it turns into muddy water,” said Quinn Symington, one of nine children who gathered at the Blue Hill Library recently to learn all about dirt.
When the children did just that, layering pebbles, silt and sand in a plastic bottle, first tapping on the side of the cup, then adding water and shaking the bottle, they discovered a phenomenon that helps explain the rocky coast of Maine—the larger and heavier pebble material “rose” to the surface in both instances.
Scientist Dave Hollenberg explained how in the outside world, smaller particles are carried by motion like wind and by water down into the soil.
“The rocks seem to move up,” he said. Then he dug for some deeper knowledge from his audience: “How do we go from rock to sand, silt and clay?”
The budding geologists were ready with answers: the wind, the water and decay.
Hollenberg agreed, and expanded on their answers. Weather, through freezing and thawing temperatures and abrasion-causing wind, results in physical disintegration of rocks. Chemical reactions, like acid rain and natural breakdown of material, or decay, causes chemical decomposition of rocks. The process takes “hundreds, thousands, and sometimes hundreds of thousands of years,” Hollenberg said.
The earth is made of layers of dirt: soil, laterite, saprolite and, finally, bedrock.
“In Maine, we call it ledge,” Hollenberg said.
Lucy Lawther, of Blue Hill, knew how the big rocks of Maine appeared. “Some of the rocks were dropped off by glaciers,” she said, and Hollenberg agreed.
He also informed the young crowd that just as Maine has a state bird, it also has a state soil, called “chesuncook,” found in mid- and northern Maine and good for growing trees.
Soil itself is 25 percent water, Hollenberg said, 25 percent gases, 45 percent minerals that come from crushed rock, and 5 percent organic matter, which Hollenberg defined as “anything that is living or at one time lived.” Soil is also full of all kinds of bacteria—one ton per acre.
The different kinds of soil—silt, sand and clay—are of increasing degrees of fineness, with clay particles “so small you can’t even see them in a microscope,” Hollenberg said.
Further experiments measured the chemicals in dirt from a flowerbed. Children added water, shook the dirt-and-water mixture up, and then filtered out the water to test its pH balance.
While waiting for the results, Hollenberg riffed on the hydrologic cycle, which the children were familiar with. Water in lakes and oceans evaporates into clouds, which release it back to the earth and ground water in the form of rain. “This cycle keeps going,” said Hollenberg.
Water is found in the ocean (96.5 percent), in glaciers (1.7 percent), in groundwater (1.7 percent) and in the air (.001 percent).
“What do we call that?” he asked of water found in air.
“Humidity,” came the quick reply.
When water freezes, it expands, occupying 9 percent more volume than as a liquid. Ice builds from the “top down because it’s less dense,” Hollenberg explained. “That’s why ice cubes float in your soda and pond ice forms on top.”
“If you turn into ice you die,” Dimitri Taras added, and everyone agreed.
The soil test results, measuring potassium and phosphorous, were then ready to read; it came up as a pH 6.5, a little on the acidic side, Hollenberg said.
“This is what soil scientists do,” said Hollenberg, concluding his session with a little quiz:
“What have you learned about soil?”
“If you want to make good soil, you have to have water,” replied Iris Kimball of Brooksville.
Taras summed it up: “Soil is an essential in life.”