Cycle 16: Rocks and the Rock Cycle

Relative Dating Done in areas with lots of sedimentary rocks Don’t need a geochronology lab Geo Time Scale developed like this before we had radiometric dating to give absolute dates. Relative Dating=sequencing of rock record, life forms and events in the evolution of life

Not just a nice view…

Correlation

“Absolute” Dating Carbon-14 dating Dating with tree rings Dating with “varves” or sediment layers in a stream Radiometric/Radioisotope dating – Measure the ratio between the radioactive parent isotope and the stable daughter product in sample. The more daughter, the older the rock. – If you know the half-life of that radioactive isotope you can get an absolute date of when that rock cooled (igneous) or was metamorphosed (metamorphic)

Class Opener: Look at the volcano diagram and igneous rocks placed on diagram: – What do all the rocks that form deep in the root of the volcanoes have in common? – How are they different than the rocks that are formed near the top/in the air above the volcano?

Crystallization Experiment Which do you think will have larger mineral crystals form? Why?

What are Igneous Rocks? All igneous rocks for from – Cooling & solidifying of magma/lava (hot liquid rock)

Two types of igneous rocks: focus on INTRUSIVE Intrusive and extrusive Igneous rocks that form from magma, underground, are called _____________ igneous rocks and they have __________ mineral xtals Large crystals form during slow cooling as atoms have a chance to move around and get organized into large atomic structures

Intrusive Igneous Rocks Rock Name#Description GraniteLarge mineral crystals. Speckled with more than 50% light colored minerals (white, pink, grey, blue) DioriteLarge mineral crystals Speckled with 50% light 50% dark minerals (green, black) GabbroLarge mineral crystals Speckled 100% dark minerals

Two types of igneous rocks: focus on EXTRUSIVE Intrusive and extrusive Igneous rocks that form from magma, near/at surface, are called _____________ igneous rocks and they have __________ mineral xtals Snall crystals form during fast cooling as atoms DO NOT have a chance to move around and get organized into large atomic structures

EXtrusive Igneous Rocks Rock Name#Description Rhyolitesmall mineral crystals. Speckled with more than 50% light colored minerals (white, pink, grey, blue) Andesitesmall mineral crystals Speckled with 50% light 50% dark minerals (green, black) Basaltsmall mineral crystals Speckled 100% dark minerals

Super-Extrusive Igneous rocks Lava shot into the air cools soooo quickly that there are no mineral crystals…these rocks are made of randomly arranged atoms. Rock Name#Description ObsidianGlassy, black (although can vary) few to no mineral crystals, some gas holes, circular fracture pattern. PumiceLots of holes, color varies from light grey to red to black. So lightweight it floats!

Why does granite sometimes form and gabbro forms other times…both form from magma cooling slowly? Depending on what part of Earth’s crust is melted into magma, it will have a different composition (set of atoms to make minerals) Type of CrustRocks FormedColor/comp Ocean Floordark Continental Crustlight Coastal (both)50%-50%

Check on your experiments Which one had the larger mineral crystals? Why? The faster the magma/lava cools, the _________ the mineral crystals The trial on ice represents… The trial on the hot plate represents…

Class Opener: Review Igneous Rocks How do igenous rocks form? What does the size of the mineral xtal of an igneous rock tell you? What does the overall “color” (percent light to dark minerals) of an igneous rock tell you?

Absolute Dating While early geologists like William Smith could only determine the relative ages of rock layers (sequencing them), today geologists can determine the ______________ age of a rock using ______________________________ of radioactive elements in minerals from ____________________ rocks What minerals are used and why? – Zircons – Because they are common in igneous rocks, resistant to weathering, contain some amount of radioactive uranium

Radioactive Decay What causes an element to be radioactive? – Happens if the nucleus of an atom (protons and neutrons) is “unstable” meaning the force that binds it together is not strong enough so particles are given off – Called radioactive decay What happens during radioactive decay? – Energy and particles released, – produces a different element – Same amount of mass left – Stops when a “stable” nucleus is formed – Rate at which it occurs is logrithmic and measureable

Half-life: – The amount of time it takes for half of the radioactive substance to react and become a different, more stable element.

How much radioactive strontium is there at time 0? How much after 27 years? How much after 54? 108? What is the pattern in decorease of mass? What happens to the mass of strontium as it decays?

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Metamorphic Rocks All metamorphic rocks form from…(one or both of the following)… – HEAT that does NOT melt the rock into magma but allows the atoms that make up minerals to re- arrange into new minerals or grow together – PRESSURE that causes the minerals to re-arrange themselves into new patterns

HEAT & Metamorphism Chemical changes do not happen to minerals below __________. Above ________ the minerals don’t just change, they MELT! Rocks can get these hot temperatures from being near or touching ______________

PRESSURE & Metamorphism Pressure can come from _______________________ or from ________________________and can cause minerals to align into bands or stripes

Foliated Metamorphic Rocks Rock NameRock #Characteristics GneissWavy ands of alternating light and dark minerals SchistSilvery bands SlateLooks like a very smooth shale, breaks into very flat thin pieces

NONFoliated Metamorphic Rocks Rock NameRock #Characteristics Anthracite CoalBlack, lightweight, somewhat soft compared to other rocks QuartziteComes in lots of colors like pink, white, & grey. Glassy looking but pretty smooth feeling. DOES NOT react to acid MarbleComes in lots of colors like pink, white, & grey. Can contain fossils. DOES react to acid.