The geologic column shows a record of how the rocks which form the Earth's crust were laid down over time. Time on a geologic column is measured in hundreds of millions of years.

A geologic column can be used to show important events, like the formation of fossil fuels, in relationship to the present.

During the CARBONIFEROUS PERIOD (280-345,000,000 years ago), much of the earth was covered with swampy tropical forests which were sometimes flooded by shallow seas. Geologists believe that the tiny creatures and plants which lived and died in these seas formed a thick layer of decaying matter which eventually turned to rock.

The climate changed at the beginning of the PERMIAN PERIOD (230-280,000,000 years ago) . The seas dried up and were replaced by deserts. During this time, the continents were constantly moving, crashing and crumpling into each other. The layers of decaying vegetation were covered by rocks, sand and silt. These layers of rock were compacted as more rock, mud and sand were layered on top of them. Great heat and pressure caused the decaying sea creatures to give up oxygen, transforming into hydrocarbons. The rocks in which the hydrocarbons formed are called source rocks, like shale.

The TRIASSIC AND JURASSIC PERIODS (181-230,000,000 years ago) followed with the great development of early reptiles including the dinosaurs. The first true primitive mammals developed along with the first reptile-like birds. There were volcanic eruptions, but the climate was uniformly warm with some dry areas.

Continued movements in the earth's crust and pressure from the rocks above forced the hydrocarbons to slowly rise up through layers of sand, sandstone, and limestone. Dakota Sandstone rock, where most natural gas in the western United States is found, was formed in the CRETACEOUS PERIOD (63-135,000,000 years ago). This was a time of grand mountain making; the chain of the Rockies appeared in western North America. Dinosaurs and other reptile forms dominated for millions of years, but finally ended in total extinction. Snakes, birds and small mammals lived on flowering plants which spread over much of the earth, replacing many earlier types of vegetation.

Native American traditional stories come from oral traditions. Not only were these stories meant to entertain, they were meant to teach. The stories were generally told aloud. As Josept Bruchac also points out, "It is important to remember to listen. There are stories all around you."

Often Native American stories reflected their view of the world which had many layers or levels. It was possible to move between the levels. The storytellers also gave animals, plants or insects "human" characteristics.

Imagine a Native American story to explain the geology of the Earth.