Principle of Superposition Determining the Relative Age of a Geologic Area

Principle of Superposition In a stack of undisturbed sedimentary rock layers, the layers on the bottom were deposited before the layers on top. Relative age tells how old something is when compared to something else.

Superposition and the Fossil Record Layers of rocks are called strata. Four principles help geologists study strata and interpret the rocks’ history. Superposition Cross-cutting relationships Original horizontality Original lateral continuity

Principle of Cross-cutting Surface Impact Crater Two Basic Rules of Relative Age Dating Cross-Cutting Relationships Principle of Superposition The surface of Mars has been hit with an impact crater. The impact crater and surface of Mars has been cut by another feature called a fracture. The fracture is the CROSS-Cutting feature. Using Relative Age Dating techniques, the surface is the oldest, the impact crater the next oldest, and the channel is the youngest. This is called Relative Age Dating by Cross-cutting relationships. Principle of Cross-cutting

Principle of Superposition Two Basic Rules of Relative Age Dating Cross-Cutting Relationships Principle of Superposition This demonstrates the Principle of Superposition. Crater #1 is partly covered crater #2, so crater #1 is older. Crater #2 is partly covered by crater #3, which makes crater #2 older than crater # 2 older than crater #3. By the Principle of Superposition, crater #1 is the youngest feature, This is known as the principle of Superposition. Principle of Superposition

Principle of Superposition Relative Age Dating Oldest Feature? Younger Feature? Youngest Feature? A = Oldest C = Youngest B = 2nd Oldest Based on the two relative age dating principles (cross-cutting relationships and superposition) let’s interpret the relative ages of the features in this image. We’ll make the inference that the surface is the oldest feature, so we are Relative Age Dating the features A,B, & C Principle of Superposition

Original horizontality Remaining Principles Original horizontality

Sedimentary rocks form layers that cover large areas. Original lateral continuity: Sedimentary rocks form layers that cover large areas.

Fossils and Relative Age Geologists keep track of which fossils came from which strata and apply the principle of superposition. Fossil occurrences in layers are used to confirm or assign relative ages to rock strata.

C original lateral continuity D uniformitarianism What principle states that processes at work today are the same processes that occurred in Earth’s past? A superposition B relative age C original lateral continuity D uniformitarianism Lesson 1 Review

What type of rock is formed when put under extreme pressure or heat? A igneous B metamorphic C strata D sedimentary Lesson 1 Review

What process slows or stops sediments in low areas of the landscape? A deposition B lithification C weathering D transportation Lesson 1 Review

Steno’s Principle page 290 Select one of Nicolas Steno’s four principles of Relative Age Dating Create a drawing that represents that principle. Label your drawing Write a summary explaining your diagram Due Friday Steno’s Principle page 290

End of Lesson 1