Notes: Relative Ages of Rock Chapter 7, Lesson 1

Modern Geology James Hutton was the first person to realize that one process formed rock and another process tore it down.

Uniformitarianism Scientists can observe the processes that are active today, and interpret what happened in the past.

Uniformitarianism Uniformitarianism states that the same Earth processes have been at work for a very long time. Geological processes that are at work today were also at work in the past. Geological processes are so slow that direct observation is not possible.

The Rock Cycle The rock cycle is a series of processes that make and change rocks through: heating melting cooling uplift weathering burial increasing pressure

The Rock Cycle

Three Major Types of Rocks Igneous Rocks - produced when magma solidifies

Three Major Types of Rocks Metamorphic Rocks - any rock that is put under extreme pressure or heat

Three Major Types of Rocks Sedimentary Rocks - form from compacted and cemented sediments

Sediment Formation and Layering Sedimentary rocks form from preexisting rocks. Four steps in the formation process: 1.Weathering 2.Transportation 3.Deposition 4.Lithification

Sediment Formation and Layering

1. Weathering Weathering is the physical or chemical breakdown of rocks into smaller pieces.

1. Weathering Physical weathering breaks down rocks without changing the mineral composition.

1. Weathering Chemical weathering changes the mineral composition of rocks.

1. Weathering

2. Transportation Transportation occurs when sediments move downhill to lower areas and come to rest.

2. Transportation Clasts are different-sized sediments (from large boulders to microscopic bits of rock) that require different amounts of force to move them.

3. Deposition Deposition occurs when sediment being transported by water, wind, or a glacier slows down or stops.

3. Deposition This usually happens in low areas called depositional environments. Two characteristics are parallel horizontal layers and sorting.

4. Lithification Lithification occurs when older sediment layers become compacted beneath younger layers. Mineral-rich liquids seep into the pore spaces between the sediment grains. The water evaporates and the minerals are left behind to cement the grains together.

Superposition and the Fossil Record Layers of rocks are called strata.

Superposition and the Fossil Record 4 principles help geologists study strata and interpret the rocks’ history: 1.Superposition 2.Original horizontality 3.Original lateral continuity 4.Cross-cutting relationships

1. Principle of Superposition In a stack of undisturbed sedimentary rock layers, the layers on the bottom were deposited before the layers on top.

1. Principle of Superposition Relative age tells how old something is when compared to something else.

1. Principle of Superposition

2. Principle of Original Horizontality Rock layers are originally deposited in horizontal, or nearly horizontal, layers.

3. Principle of Original Lateral Continuity Sedimentary rocks form layers that cover large areas.

4. Principle of Cross-Cutting Relationships A layer or feature that cuts across other rock layers is younger than the layer(s) being cut.

Principles

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.

Fossils and Relative Age

With relative age, we compare the age of one rock to the age of other rocks. Example: “This rock is older than that rock.”

Fossils and Relative Age With absolute age, we know the number of years since a rock formed. Example, “This rock is 1 million years old.”

Fossils and Relative Age Certain fossils, called index fossils, help geologists match rock layers. Index fossils are useful because: 1.They are widely distributed. 2.They tell the relative ages of rock layers in which they occur. 3.They represent a type of organism that existed only briefly.

Index Fossils

What principle states that processes at work today are the same processes that occurred in Earth’s past? Asuperposition Brelative age Coriginal lateral continuity Duniformitarianism 7.1 Relative Ages of Rocks 1.A 2.B 3.C 4.D

What type of rock is formed when put under extreme pressure or heat? Aigneous Bmetamorphic Cstrata Dsedimentary 7.1 Relative Ages of Rocks 1.A 2.B 3.C 4.D

What process slows or stops sediments in low areas of the landscape? Adeposition Blithification Cweathering Dtransportation 7.1 Relative Ages of Rocks 1.A 2.B 3.C 4.D

What term describes the physical or chemical breakdown of rocks into smaller pieces? Adeposition Berosion Clithification Dweathering 1.A 2.B 3.C 4.D

What principle states that the bottom layers of sedimentary rocks were deposited before the top layers? Alithification Buniformitarianism Csuperposition Doriginal horizontality 1.A 2.B 3.C 4.D

What process includes heating, melting, cooling, uplift, weathering, and increasing pressure? Asediment formation Bmetamorphic rock formation Cigneous rock formation Dthe rock cycle 1.A 2.B 3.C 4.D

What does the principle of original lateral continuity state? Alayers on the bottom are deposited before layers on the top Bsediments are deposited horizontally Csedimentary rocks form layers that cover large areas Dsediments always remain horizontal SCI 4.c 1.A 2.B 3.C 4.D

Which type of rock is the most useful for relative dating? Aigneous Bsedimentary Cmagma Dmetamorphic 1.A 2.B 3.C 4.D

The relative age of something is _____. Aits age in relation to Earth Bits age in comparison to other things Cits age since it was discovered Dits age since it died 1.A 2.B 3.C 4.D

Igneous Sedimentary Metamorphic