What exactly are sedimentary rocks?
Sediments begin as solid fragments suspended in water or some other liquid. They are made of heavier materials than the surrounding liquid and they tend to sink to the bottom. However, sediments tend to settle more slowly when the liquid is turbulent. Tea leaves sink to the bottom of the pot, and so do gritty grains of come. These dregs are sediments that have settled down because they weigh more than liquid tea or coffee. If you shake the pot, they tend to float around. But as the liquid becomes calm, they settle down again. This sedimentary process goes on in nature on a grand scale. The process is slow but when aided by certain changes in the landscape, it adds massive layers of rock to the crust of the earth. Sedimentary rocks begin as fragmentary solids suspended in lakes and rivers, swamps and seas. Dusty fragments build up silty deposits, especially where rivers meet the sea. All kinds of suspended fragments abound in the ocean and form sedimentary layers as they sift down to se
How do plants and animals get caught in the layers? Make a relative timeline of events for the fossil you dug up earlier. Start when sediment formed and end with taking it to the museum. Read more about Fossils and Rocks, Fossil Succession, and The Numeric Time Scale. Why do scientists sometimes need to adjust the geologic timeline? How does each “law” you’ve learned about describe a sequence of events? Lastly, check out what kinds of geologic changes have happened in your own state by Exploring Time & Space at The Paleontology Portal. First, click on each time period name listed at the top right corner of the screen. Each link will show you where experts think the continents existed in relation to one another during that period. Then, using the map of the United States, look for where the oldest rock layers are found at the surface, then the next oldest, and so on. After reviewing the large-scale sequence, zoom into your state. On a paper outline of your state, draw in the different g
