The Mississippi River has served as the major drainage basin for North America for millions of years, depositing layers upon layers of sediment. When they die, millions of tiny organisms such as nannoplankton and faraminefera can become trapped and buried in this sediment and become fossils. Geoscientists use these fossils to describe the original depositional environment, water depth, and when the sediment was deposited in geologic time.
A basic geologic principle tells us that the older layers, or “strata” are found below younger layers. From this principle, we can determine the “relative age” of of a fossil. A fossil found in deeply buried sediments is relatively older than a fossil found above it. Sophisticated dating techniques can tell us the absolute age of a fossil. For example, one fossil became extinct 2.2 million years ago.
Geoscientists use sound waves or seismic energy to image the subsurface. Sound bounces off the many strata, allowing geoscientists to create maps and models of the layers below the earth’s surface.
Geologists travel the world to study rock outcrops to compare to the present-day GOM. The desert in the Guadalupe Mountains was once deep underwater during the Permian period (250 million years ago). Fieldwork all over the world enables geoscientists to examine rocks similar to those reservoir rocks now buried deep in the GOM.
Methane gas and water can form frozen crystals deep on the ocean floor. These crystals called gas hydrates that form under great pressures and cold temperatures. When these crystals mix with seafloor sediment, they can form thick, solid layers or mounds.