Case Study: What Lies Beneath?

Mars Exposed

A group of students exploring Google Earth discovered that they could use it to view the surface of Mars just as they would their own planet. Unlike Earth, however, they found no roads or houses, no rivers or forests and no oceans. What they did find was the entire exposed surface of rocks and soils. It was a geologist's dream come true! Every dune, crater and outcrop was visible from the air. The images were awesome! Very quickly they began to find geologic features that resembled some they had seen while viewing the Earth's landscape.

Scientists can use features like those seen on the Martian surface to reconstruct its geologic past. To date, many formations that have glacial origin have been observed on the Martian surface. One of the biggest limitations to those studies is the relatively low resolution of the images. In simple terms: you can only see really big features. One such glacial feature also found here on Earth is the mega-scale glacial lineation.

Landsat Images and Mega-Scale Glacial Lineations

Since they were first observed in Landsat images of northern Canada almost twenty years ago, mega-scale glacial lineations (MSGL) have been hypothesized to be the result of fast-flowing paleo-ice streams associated with the retreat of the North American Ice Sheet (Clark, 1993). These geologic features are massive waveforms in the landscape running parallel to ancient ice flow. Typically MSGLs range from 8 to 70 km in length with widths of 200m to 1300m and spacing ranging from 300m to 5km (Clark, 1993). There is broad agreement that mega-scale glacial lineations are direct evidence of the extent and flow direction of grounded ice during the Last Glacial Maximum.

Like its Martian counterparts, each of these features can be used to make inferences about the past behavior of glaciers. But even here on our home planet there is a catch: unlike Mars, the Earth is largely covered with water! This means that to study these formations we need special tools. In this chapter, you will be tracing the route that ice sheets moved thousands of years ago by mapping mega-scale lineations found on the sea floor.

Before you begin, however, you will need to better understand how scientists "see" the bottom of the sea. Before you continue on to the Step-by-Step instructions, take time to review and discuss the two attached articles: