LOOKING BENEATH How scientists gather information from sediments

National Science Standards  Science and Technology Standard – 5-8: Abilities of technological design  Earth and Space Science: Structure of the earth system

Law of Superposition  It is like a laundry basket, the clothes are piled in by the day you wore them.  You can dig back a couple of days ago through the days before.  The layers of clothes can tell a story.

Law of Superposition  In sedimentary rocks, deposition creates layers of new “stuff” or material on top of older stuff.  In some places these layers of sediments are compacted over time to make sedimentary rocks.

Law of Superposition  Scientists use this law to look backwards in time at what happened in a area by looking at how they are layered, and what they are made of.  Think of it like explaining of how a Snickers Bar is made. Which comes first, the nuts or the nougat? How do you know? How can you tell if the milk chocolate has been melted at some point, or the wrapper was opened?

How scientists use it  In the ocean or in lakes, a fine “rain” or sediments collects on the seabed or lake bottom.  Depending on what the sediment is made from, how thick it is and what fossils are in it, scientists can tell a lot about an area.

 Scientists can tell what lived there from fossils or shells  Scientists can tell if it was cold or really wet, track changes in water chemistry, and tell if a regular pattern was disrupted by a catastrophic event, such as an underwater landslide or tsunami.

Collecting sediments  There are different ways to collect sediments.  It depends on how deep the sediment is and what they are looking to explore.

Long Cores  Sediment cores that are really big can be collected in tubes.  Long tubes are pushed into the seabed by ROVs or other machines.  These tubes collect sediment much like a straw being pushed into cake.

 The cores are opened by splitting the tube in the middle.  One half is called the working half – this is where scientists take samples and make measurements.  The other is left alone and called an archive half. It is a record of what the core looked like before it was studied.

 Scientists describe the working half of the core, take pictures, scan the images into a computer, run chemical tests on the sediments and look at the type of animals.

 To keep the cores from rotting and growing mold, they are covered with plastic and kept moist in great big refrigerators.

 If a “scoop” of sediment is needed from the seabed, a grab basket might be used.

 Some sediment cores are collected in boxes.  Some cores are collected in slices, like a cake.  Some cores are very tiny.  It depends on how much is needed and where it is being collected from.

Other types of cores -  Tree cores  Ice cores

Design your own:  How could you create a sediment core tool to take a sample of and what do you think it would show-  a cupcake?  a carrot?  ground in your backyard?  a baseball?  a bowling ball?

Bibliography  USGS Menlo Park, CA - most core photos  How do the cycles and modes of the Pacific Ocean affect the water cycle? ecosystem/by-theme/ ecosystem/by-theme/3213  Ice and Sediment Cores ideas/ice-and-sediment-cores/ ideas/ice-and-sediment-cores/