Chapter Menu Lesson 1:Relative Ages of RocksRelative Ages of Rocks Lesson 2:Absolute Ages of RocksAbsolute Ages of Rocks Click on a hyperlink to view the corresponding lesson.

uniformitarianism rock cycle clast lithification stratum superposition relative age 7.1 Relative Ages of Rocks

The Beginning of Modern Geology James Hutton was the first person to realize that one process formed rock and another process tore it down. 7.1 Relative Ages of Rocks

The Principle of 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. 7.1 Relative Ages of Rocks Scientists can observe the processes that are active today, and interpret what happened in the past.

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 7.1 Relative Ages of Rocks Metamorphosis

The Rock Cycle (cont.) 7.1 Relative Ages of Rocks How are materials from the earth broken down?

The Rock Cycle (cont.) 7.1 Relative Ages of Rocks

Three Major Types of Rocks Igneous rocks –produced when magma solidifies Metamorphic rocks –any rock that is put under extreme pressure or heat Sedimentary rocks –form from compacted and cemented sediments 7.1 Relative Ages of Rocks

Sediment Formation and Layering Sedimentary rocks form from preexisting rocks. Four steps in the formation process: –Weathering –Transportation –Deposition –Lithification 7.1 Relative Ages of Rocks

Weathering Weathering is the physical or chemical breakdown of rocks into smaller pieces. –Physical weathering breaks down rocks without changing the mineral composition. –Chemical weathering changes the mineral composition of rocks. 7.1 Relative Ages of Rocks

Weathering (cont.) 7.1 Relative Ages of Rocks

Transportation Transportation occurs when sediments move downhill to lower areas and come to rest. Clasts, different-sized sediments such as large boulders to microscopic bits of rocks that require different amounts of force to move them. 7.1 Relative Ages of Rocks

Deposition Deposition occurs when sediment being transported by water, wind, or a glacier slows down or stops. 7.1 Relative Ages of Rocks This usually happens in low areas called depositional environments. Two characteristics are parallel, horizontal layers, and sorting.

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. 7.1 Relative Ages of Rocks

Superposition and the Fossil Record Layers of rocks are called strata. Four principles help geologists study strata and interpret the rocks’ history. –Superposition –Original horizontality –Original lateral continuity –Cross-cutting relationships 7.1 Relative Ages of Rocks

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. 7.1 Relative Ages of Rocks

Remaining Principles Original horizontality: –Rock layers are originally deposited in horizontal, or nearly horizontal, layers. Original lateral continuity: –Sedimentary rocks form layers that cover large areas. Cross-cutting relationships: –A layer or feature that cuts across other rock layers is younger than the layer(s) being cut. 7.1 Relative Ages of Rocks

Remaining Principles (cont.) 7.1 Relative Ages of Rocks

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. 7.1 Relative Ages of Rocks

Lesson 1 Review 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

Lesson 1 Review 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

Lesson 1 Review 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

End of Lesson 1

isotope radioactive decay half-life 7.2 Absolute Ages of Rocks

What is Earth’s Age? Scientists discovered and used a natural “clock” to date the age of Earth, meteorites, and the moon. 7.2 Absolute Ages of Rocks Scientists used this natural clock to determine the age of bog bodies.

Atoms and Isotopes Atoms are the microscopic building blocks of all matter on Earth. 7.2 Absolute Ages of Rocks

Atoms and Isotopes (cont.) An isotope is the term for atoms of an element that have the same number of protons, but a differing number of neutrons. Carbon isotopes—carbon-12, carbon-13, carbon-14—have 6, 7, or 8 neutrons. 7.2 Absolute Ages of Rocks

Radioactive Decay Radioactive decay occurs when an unstable nucleus changes into another nucleus by emitting particles and energy. 7.2 Absolute Ages of Rocks

Parent and Daughter Isotopes The isotope that undergoes radioactive decay is the parent isotope. The stable form of the element that forms is the daughter isotope. 7.2 Absolute Ages of Rocks

Half-Life Parent isotopes decay into daughter isotopes at a constant rate—the decay rate. The half-life of an element is the calculated length of time it takes for half a specific amount of a parent isotope to decay. 7.2 Absolute Ages of Rocks

Half-Life (cont.) 7.2 Absolute Ages of Rocks

Radiometric Dating Scientists use radiometric dating to calculate absolute ages of rocks and minerals. –Comparing the amount of parent to daughter material determines the number of half-lives the material has been through. –Igneous rock is most commonly used for radiometric dating. 7.2 Absolute Ages of Rocks

The Absolute Age of Earth Rock grains from continental shields— where the oldest rocks on Earth occur—are estimated to be 4.0 to 4.4 billion years old. 7.2 Absolute Ages of Rocks

Meteorites and the Moon Scientists used radiometric dating to determine the ages of meteorites and the Moon. The closeness of calculated ages of Earth, the Moon, and meteorites helps confirm that the entire solar system formed at the same time. 7.2 Absolute Ages of Rocks

Lesson 2 Review The isotopes of an element have a different number of what? Aprotons Bneutrons Celectrons Datoms 7.2 Absolute Ages of Rocks 1.A 2.B 3.C 4.D

Lesson 2 Review What important feature of radioactive decay has allowed geologists to date Rocks? Athe isotopes of an element may be stable or unstable Bthe nucleus gains or loses protons Cparent isotopes decay into daughter isotopes Dthe decay occurs at a constant rate 7.2 Absolute Ages of Rocks 1.A 2.B 3.C 4.D

Lesson 2 Review What do scientists use to measure the absolute age of a rock? Aradiometric dating Bamount of carbon in the rock Cabsolute dating Drelative dating 7.2 Absolute Ages of Rocks 1.A 2.B 3.C 4.D