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Unlocking Puzzles of the Past Core Samples What is a Sediment Core? • A sediment core is a long piece of sediment collected from the bottom of a body of water. • The core is analyzed to reveal evidence of organisms that lived during sediment formation. How is a Core Collected? Pushing the empty tube into the mud Tube containing sediment core is carried out of the pond Researchers push an empty tube into the pond bottom and use suction to pull out a core of sediment How is a Core Collected? Removing a core from the tube The sediment core is removed from the empty tube in one continuous piece How is a Core Collected? Measuring and describing a core Wrapping a core The sediment core is described, carefully wrapped up, and taken back to the lab for study What Can We Find In Cores? • Plant macrofossils are preserved seeds, leaves or other plant segments useful in identifying plants. • Plant microfossils are tiny pollen grains and spores that are also useful, but can only be identified with a very strong microscope. Seed Pollen grains Leaf fragment What Can We Find In Cores? • We also can find signs of human activity such as charcoal from fires or metal from industrial activities Industrial particle Relative Dating ← Top of Core ← Older macrofossils are found at deeper levels ← Bottom of Core Since shallow layers settled later, macrofossils found higher are younger than those found in deeper levels. Relative Dating Relative dating of fossils doesn’t give information about actual age of the fossils but it does allow researchers to understand how the ecological community changed over time. Relative Dating By identifying plant macrofossils throughout the core, it’s possible to tell which plants were present when each sediment layer was formed. Compression The correlation between fossil depth and age is difficult to determine due to several factors including compression. Compression As sediment layers settle one atop another, top layers create pressure on lower layers. The excess weight presses the lower layers tightly together. Sediment compression is exaggerated when the core is pressed into the tube to be withdrawn. Why study Miller Woods? The Miller Woods are home to 150 ponds that are the last remnants of a once extensive pond system. Why study Miller Woods? The ponds formed in rows as glaciers, and Lake Michigan, retreated to the North in a process of melting, stalling and melting 15,000 years ago. Glaciers covered Michigan 20,000 years ago Why study Miller Woods? • Henry Cowles, for which Cowles bog is named, reported upwards of 50 rows of ponds in the area in the early 1900s. Today only a few remain with the rest having been taken over by industry and housing. Why study Miller Woods? • These ponds contain many unique groups of plants and animals that need to be protected. • We need to understand about how and why the plant communities have changed so we can protect them for the future In this set of Activities… • You will collect data from a sediment core to better understand how relative dating is used to track ecological changes. • You’ll compare the species that lived there through time and explore a connection to these changes and the spread of human development. • Finally you will collect a core from a local pond to appreciate the methods involved.