The Rock and Fossil Record Chapter 15 Time Marches On Looking at Fossils Earth’s Story and Those Who First Listened Relative Dating: Which Came First?

The Rock and Fossil Record

Chapter 15Time Marches On

Looking at FossilsEarth’s Story and Those Who First

ListenedRelative Dating: Which

Came First?Absolute Dating: A Measure of Time

Terms You Must Know• Uniformitarianism• Catastrophism• Paleontology• Relative dating• Superposition• Geologic column• Unconformity• Absolute dating• Isotope• Radioactive decay• Radiometric dating• Half-life

• Fossil• Trace fossil• Mold• Cast• Index fossil• Geologic time scale• Eon• Era• Period• Epoch• extinction

Earth’s age =4,600,000,000 or 4.6 billion years old

Grand Canyon: history revealed

Reading this rock book shows:

periods of mountain buildingadvancing and retreating shallow seasevolution of faunas

Nearly 2 billion years of history are preserved in the rock layers of the Grand Canyons 2 km depth.

• The relative geologic time scale has a sequence of – eons - largest divisions of geologic time

– eras – second largest division

– periods – third largest division

– epochs – fourth largest division

– but no numbers indicating how long each time frame occurs occurred

Relative Geologic Time Scale

• Large divisions based on characteristics of fossils

• Paleozoic Era – early life dominated by invertebrate animals

• Mesozoic Era – middle life dominated by reptiles

• Cenozoic Era – recent life dominated by mammals

Geologic Time Scale

What marks the close of one geologic time frame and the dawn of another?

Either there is a mass extinction or a higher order life form

begins to dominate or both events occur!

Extinction = there is a death of every member of the species – they are permanently gone!

• The discovery of radioactivity near the end of the 1800s allowed absolute ages to be accurately applied to the relative geologic time scale

• The geologic time scale is a dual scale– a relative scale (near accurate)

– and an absolute scale (accurate)

Geologic Time Scale

• The concept and measurement of geologic time has changed through human history!

• James Ussher (1581-1665) in Ireland – calculated the age of Earth based on recorded history and genealogies in Genesis•he announced that Earth was created on October 22, 4004 B.C.

•a century later it was considered heresy to say Earth was more than about 6000 years old

Changes in the Concept of Geologic Time

• During the 1700s and 1800s Earth’s age was estimated scientifically– Georges Louis de Buffon (1707-1788) calculated how long Earth took to cool gradually from a molten beginning •used melted iron balls of various diameters

•he estimated Earth was 75,000 years old– Others used rates of deposition of various sediments and thickness of sedimentary rock in the crust •gave estimates of <1 million •to more than 2 billion years

– Or the amount of salt carried by rivers to the ocean and the salinity of seawater •John Joly in 1899 obtained a minimum age of 90 million years

So what is today’s date?

• Today is the ____ day,• __first__ month,• __second__ decade,• __21st__ century,• __third__ millennium,• __holocene__ epoch, • __quaternary__ period, • __cenozoic__ era and the __phanerozoic__eon.

Why did the dinosaurs all die?

Ideas: meteor hit, asteroid strike, volcanic eruptions, earthquakes, wildfires, drought, flood, famine, sea level rise, glacial advance, continental drift/climate change, boredom, over hunting…

*We only have theories and fossils to guide us!

Fossils – remains of dead plant or animal that have

been preserved• Fossil facts:

• -they are rare due to rock cycle and mining processes

• -they are usually found in

sedimentary rock• -casts are made for museums & sale

• Casts are made from a hollow

mold• -vertebrates make the best fossils (have

hard body parts)• -invertebrates,

have too many soft body parts

Types of Fossils• 1. Plain fossils are Mother Nature’s cast copy of a formerly living organism made from layers of sediment that have turned into stone = sedimentary rock!

• 2. Imprint fossils are flat carbonaceous films of a formerly living organism such as a fish or plant. They are 2D.

• 3. Frozen fossils are nearly whole organisms preserved in glacial ice. Little decay occurs due to freezing temperatures and few bacteria. These are 3D.

• 4. Petrified fossils used to be bone or wood that has been replaced by layers of sediment to create a stone copy of the once living species. The process is known as petrification.

• 5. Amber is hardened tree sap or rosin that has mineralized with heat, pressure and time. Organisms trapped in the tree sap are perfectly preserved. They are usually small creatures like insects, lizards or frogs.

• 6. Trace fossils are those fossils that are naturally preserved evidence of some animal activity such as footprints, burrows and coprolites. They are not the organism itself.

Mold vs. Cast• Cast – object created when sediment fills mold

• Mold – hollow cavity created by fossil cast• Latex molds are used to create fake cast fossils for museum displays, schools, stores…

Fossil type Advantage Disadvantage

Plain fossil 3D, see size dimensions, near exact copy

Mineral replacements, hard body parts only

Imprint See perfect size dimensions, flat copy

2D

Frozen fossil 3D, real organism Thawing would destroy fossil

Petrified fossil 3D, see size dimensions, near exact copy

Rock copy, not the real deal

Amber 3D, real organism, gemstone value

Cutting/breaking open would destroy fossil and valuable gemstone, only small organisms

Trace fossil Tells us about their activity

Not the organism itself

• 1. Uniformitarianism – the notion that the geologic processes actively forming Earth today are the same that have been active in the past and are unchanged– Two main processes are erosion and

deposition– developed in 1788, by geologist James

Hutton– Studied rock formations for 30 plus years

in England and Scotland– Now a widely held principle today, in part

thanks to the addition of Charles Lyell’s research and writings in the 1830’s

Uniformitarianism

• 2. Catastrophism – opposing idea to Hutton’s – states that the Earth’s features were created suddenly through catastrophes

– Proposed by Georges Cuvier (1769-1832)

– Dominated European geologic thinking

– Biblical events were referenced– Was used to explain extinctions

Catastrophism

People To Know• James Hutton• Charles Lyell• Georges Cuvier

Siccar Point• Hutton’s theories sparked

a scientific debate• In Hutton’s time, people

believed that the Earth was only a few thousand years old.

• What Hutton proposed could not happen in just a few thousand years

• He formed his theories by observing the geologic processes at Siccar Point

• Deposition and folding were observed

Idea of Modern Geology???

• Modern scientists like Stephen Gould have challenged Lyell’s uniformitarianism.

• Today scientists believe that catastrophes do at times play an important role in shaping Earth’s history.

• Most geologic change is gradual and uniform but catastrophes have caused geologic change.

• Ex. Craters formed due to asteroids and comets

Unconformity• 3. Unconformities – are

irregularities found in a geologic column of soil, these irregularities are due to either erosion or missing deposition.– Unconformity is a break

in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.

Unconformity at Siccar Point

Unconformity

• When a geologists finds an unconformity, they must question whether the “missing layer” was never present or whether is was somehow removed

• Nondeposition- stopage of deposition when a supply of sediment is cut off

• Erosion can create unconformities.

3 Types of Unconformity

• Disconformities– Most common– Part of a sequence

of parallel rock layers is missing

• Nonconformities• Angular

unconformities

A. Disconformities – occurs when erosion carries away deposition, which stops for a while, then deposition begins again

What’s missing?

Disconformity

• Disconformities are much harder to recognize in the field, because often there is no angular relationship between sets of layers. Disconformities are usually recognized by correlating from one area to another and finding that some strata is missing in one of the areas.

B. Nonconformities – non-layered igneous intrusions (lava) are pushed up from inside the Earth and are eroded in the upheaval, while deposition occurs on top, hiding the top eroded area

What’s missing?

Nonconformity

• Nonconformities occur where rocks that formed deep in the Earth, such as intrusive igneous rocks or metamorphic rocks, are overlain by sedimentary rocks formed at the Earth's surface. The nonconformity can only occur if all of the rocks overlying the metamorphic or intrusive igneous rocks have been removed by erosion.

Nonconformity

• Notice that there is an "intersection" of a vertical rock butting up against a horizontal sock. In an unconformity, it is two of the same type of rock (e.g. sedimentary & sedimentary). A nonconformity is two layers of different types (e.g. igneous & sedimentary).

C. Angular unconformities – occurs when rock layers have been tilted or folded and then eroded before more horizontal deposition happens on top

What’s missing?

Angular unconformity

• Angular unconformities are easy to recognize in the field because of the angular relationship of layers that were originally deposited horizontally.

Example of an Unconformity

• Tilted sandstone and siltstone below, conglomerate above

www.geology.sdsu.edu/visualgeology/geology101/erosion6.htm

http://http://www.wwnorton.com/college/geo/egeo/flash/10_2.swf

Class Activity:

Listen for unconformities in this Queen hit from 1975!

Use the Vis-à-vis to denote changes in “layers” of the song (geologic column). Use a star to denote the unconformity!

http://www.kovideo.net/music/video/Queen---Bohemian-Rhapsody/24.html

Important things to remember:

A. Law of superposition - states that the older rocks lie beneath younger rocks and fossils in undisturbed areas

B. Geologic column - a section of rock layers pieced together using the law of superposition and filling in the mysteries of geologic time

C. Index fossils – fossilized organisms that are used to help date surrounding organisms and rock layers, they are known reference points in the geologic time scale

Two ways to date rocks & fossils

• 1. Relative dating•Using a set of principles to put rocks in their proper

sequences of formation• 2. Absolute dating

•Using radioactive decay to determine the exact age of rocks

• Apply:Law/Principle of Superposition– Oldest on

bottom, youngest on top

Relative-Dating Principles

Chattanooga Shale, TN

Relative dating is any method of determining whether an event or object is older or younger than other events or objects.

Relative Dating

Relative datingCan only be used when

the rock layers have been preserved in their original sequence

Helps scientists determine whether one fossil is older than the other

Disturbing Forces• Not all rock formations

are arranged with the oldest layers on the bottom.

• Natural forces can fold, tilt, break, or remove parts of the rock layer

• Geologists use a geologic column to help them

• Relative dating assumes that if rock layers are not horizontal, then something must have disturbed them after they formed.

• A dark-colored dike has intruded into older light colored granite: the dike is younger than the granite

Cross-cutting

Relationships

North shore of Lake Superior, Ontario Canada

• A small fault displaces tilted beds: the fault is younger than the beds

Cross-cutting Relationships

Templin Highway, Castaic, California

Absolute Dating:any method of measuring the exact age

of an event or object in years Most common:based on Radioactive

DecayParent daughter

Why does it work?

1. The decay rate is CONSTANT, independent of external conditions in the earth.2. The daughter/Parent ratio can be precisely measured.

Radioactive Decay• The process in which a

radioactive isotope tends to break down into a stable isotope of the same element or another element.

• Sounds great but what is an isotope?

• An isotope is an atom that has the same number of protons (atomic #) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass)

How does it work?What does this have to do with the age of

rocks?• Unstable isotope is

called parent isotopeparent isotope• The stable isotope

produced by radioactive decay is the daughter isotopedaughter isotope.

• Decay is constant!Decay is constant!• The more daughter

isotope- the older the rock!

Radiometric datingRadiometric dating• A method of

determining the age of an object by estimating the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope

• Really just a ratio of parent material to daughter material.

Half-life – the time required for one-half of the radioactive nuclei in a sample to decay

Types of radiometric dating• Potassium-argon method

– K-40 half-life 1.3 billion years– Decays into argon and calcium– Used to date rocks older than 100,00 years old

• Uranium-lead method– U-238 half-life 4.5 billion years– Decays into lead-206– Used for rocks more than 10 million years old

• Rubidium-strontium method– Rb-87 half-life 49 billion years– Decays into strontium-87– Used for rocks more than 10 million years old

• Carbon-14 method

Dating with carbon-14Dating with carbon-14 (radiocarbon dating)

-Half-life of only 5730 years-Used to date very recent events-Carbon-14 is produced in the upper atmosphere-Useful tool for anthropologists, archeologists, and

geologists who study very recent Earth history• -Carbon-14 is continuously created in the atmosphere by

cosmic radiation. -Plants absorb C-14 directly through their leaves in the

form of carbon dioxide• -Animals take in C-14 indirectly when they eat plants• -When an organism dies, it stops absorbing new C-14 and

its radiocarbon “clock” is set.

• http://www.bcscience.com/bc10/pgs/quiz_section7.2.htm

• In radioactive decay, during each equal time unit, one half-life, the proportion of parent atoms decreases by 1/2

Geometric Radioactive Decay

• Radiometric dating is the most common method of obtaining absolute ages– calculated from the natural rates of decay of various natural radioactive elements present in trace amounts in some rocks

• Other methods?– Tree ring counting (use overlapping layers from several trees)

– Varves (annually produced layer of sedimentary rock)

– Ice cores

Absolute Dating

• In cross-dating, tree-ring patterns are used from different trees, with overlapping life spans

Tree-Ring Dating Method

• Closed system is needed for an accurate date– neither parent nor daughter atoms can have been added or removed from the sample since crystallization

• If leakage of daughters has occurred – it partially resets the radiometric clock and the age will be too young

• If parents escape, the date will be too old

• Most reliable dates use multiple methods

Sources of Uncertainty

• Dating techniques are always improving– Presently measurement error is typically <0.5% of the age, and even better than 0.1%

– A date of 540 million might have an error of ±2.7 million years or as low as ±0.54 million

Sources of Uncertainty

Mass Spectrometer

www.mines.unr.edu/isotope/gallery.html

Natural Selection and the Theory of

Evolution-some scientists believe the Earth is older than previously thought because of the fossil record-the English naturalist famous for his voyages and studies is Charles Darwin

-in 1831, at the age of 22, Darwin took a five year voyage on a ship known as the HMS Beagle; he was the ship’s naturalist-Darwin continued taking mapping and collecting expeditions to the Galapagos Islands

Galapagos Critters!

-in 1836, Darwin came home for 22 years and studied his findings-Darwin developed the idea that organisms in nature “struggle for existence” (meaning all living things must compete with one another for life, food, shelter, space and mates in order to survive)

-in 1859, Darwin published a book explaining the discoveries of his and fellow scientists (Alfred Wallace) entitled On the Origin of Species by Means of Natural Selection

-some of Darwin’s ideas came from his experiments when he selected the specific traits of offspring and then bred selected farm animals to see the outcomes; this is known as artificial selection.

A mule is the offspring of a male donkey and a female horse (The much rarer offspring of a

male horse and a female donkey is called a

hinny.) They are sterile due to chromosome

differences!Horse (64) + Donkey (62) = Mule

-Darwin thought that a similar mechanism occurred in nature; the mechanism for change in an organism, with favorable variations for a particular environment he termed natural selection (meaning those without “good” genes for a specific environment are more likely to die and not pass on their genes)

The tale of the peppered moths evolution

Examples of how organisms become naturally selected

for:1. They copy the exact look of

another organism – mimicry2. They are colored to match

their environment or can change colors to match their habitat – camouflage

3. They grow structures to avoid predation and/or have for defense – bodily additions

Camouflage Examples

Mimicry Examples

Structural Adaptations Examples

4. They become able to avoid death usually caused by chemicals – pesticide and antibiotic resistanceEx. DDT

http://www.livinghistoryfarm.org/farminginthe40s/pests_02.html

http://bird-habitats.suite101.com/article.cfm/birds_and_pesticides

http://books.google.com/books?hl=en&id=HeR1l0V0r54C&dq=Rachel+Carson's+Silent+Spring&printsec=frontcover&source=web&ots=1r4cRliR4G&sig=nq1G8iequtceTz52Jif8kXW1inA&ei=JqSPSavtIJPHtgfM7OCOCw&sa=X&oi=book_result&resnum=3&ct=result#PPP1,M1

Ex. Penicillin resistant bacteria

http://www.webmd.com/skin-problems-and-treatments/understanding-mrsa-methicillin-resistant-staphylococcus-aureus

1. Don’t demand a prescription of antibiotics from your doctor, unless he or she has diagnosed your affliction as a bacterial infection that requires it.2. Take all of the antibiotics as prescribed, even if the symptoms subside. 3. Never share your antibiotics with friends or family, even if you are 100% sure that they have the same infection. Let your doctor do the exam and write a new prescription.

How to prevent antibiotic resistant infections

Comparing the structural details of features found in different but related organisms reveals a basic similarity. Ex. forelimb of mammals - human arm, cat forelimb, whale front flipper, bat wing. Although function is quite different,

they appear to be so similar structurally

Homologous structures

All vertebrate embryos have segmented muscles, gill pouches, a tubular heart

without left & right sides.

Embryological development

How evolution affects whole populations

http://bcs.whfreeman.com/thelifewire/content/chp23/2302001.html

Lyell and Darwin• Charles Darwin and Charles Lyell were good

friends.• Darwin accepted and supported

uniformitarianism• Darwin had read Lyell’s book Principles of

Geology before his famous 1831 voyage on HMS Beagle

• Despite being friends, Lyell did not embrace Darwin’s theories of natural selection.

• Much later, Lyell finally accepted Darwin’s theories.

Jamey Johnson’s “In Color”

• I said, Grandpa what’s this picture here It’s all black and white and ain’t real clearIs that you there, he said, yeah I was elevenTimes were tough back in thirty-fiveThat’s me and Uncle Joe just tryin’ to surviveA cotton farm in the Great Depression

And if it looks like we were scared to deathLike a couple of kids just trying to save each otherYou should have seen it in color

This one here was taken overseasIn the middle of hell in nineteen forty-threeIn the winter time you can almost see my breathThat was my tail gunner ole’ Johnny McGeeHe was a high school teacher from New OrleansAnd he had my back right through the day we left

And if it looks like we were scared to deathLike a couple of kids just trying to save each otherYou should have seen it in color

A picture’s worth a thousand words But you can’t see what those shades of gray keep coveredYou should have seen it in color

This one is my favorite oneThis is me and grandma in the summer sunAll dressed up the day we said our vowsYou can’t tell it here but it was hot that JuneThat rose was red and her eyes were blueAnd just look at that smile I was so proud

That’s the story of my lifeRight there in black and white

And if it looks like we were scared to deathLike a couple of kids just trying to save each otherYou should have seen it in color

A picture’s worth a thousand words But you can’t see what those shades of gray keep coveredYou should have seen it in color

You should have seen it in color