Interpreting the PastInterpreting the Past

Part 1Part 1

More Chapter 17More Chapter 17plus Chapter 18plus Chapter 18

To interpret the geologic pastTo interpret the geologic past

• History of Earth and its life can be read as a sequence of events

• Geological record events can be interpreted by a study of the present– The principle of uniformitarianism:

• Developed by James Hutton• “the present is the key to the past”• Championed by Charles Lyell in his book

Principles of Geology • Changes can be gradual or sudden

Sometimes, however, catastrophes occur.

Beginnings of relative datingBeginnings of relative datingTo make sense of the data, geologists

constructed the geologic time scale– It records major geologic events– It notes appearances, and disappearances, of

varied forms of life

The sedimentary recordThe sedimentary record

• Formed by familiar surface processes• Sediments 75% of surface-exposed rock• Sediment sequences record environments

where they accumulated• Different sequences represent different

times and places:– Evidence of past mountain belts and

coastlines, seas, rivers, lakes, etc.– Some give information about past climates

Sedimentary FaciesSedimentary Facies• Individual rock types are not specific to just a

single environment of deposition• Example: Sand that eventually becomes

sandstone may be deposited in river channels, sand dunes, beaches, a shallow ocean shelf, or a deep ocean landslide (a turbidite), etc.

Sedimentary Rock InterpretationSedimentary Rock Interpretation

• To identify the depositional environment for a sedimentary rock body, we must consider:

• Sedimentary structures• Fossils & the “niche” of modern

counterparts - define• The relationships to other sedimentary

rock units both above and below and laterally i.e. the sedimentary facies

StratigraphyStratigraphy• The study of sedimentary rock sequences

• Layering of sedimentary rock is the

result of grain size or grain composition changes during deposition

• The changes record:

(a) Tectonic activity

(b) Rising or falling sea level

(c) Climate changes

(d) Variations in sediment type deposited

Division of stratigraphic sequencesDivision of stratigraphic sequences

• We need discrete units to define lateral and vertical rock relationships “lithostratigraphic”

• The most commonly used stratigraphic unit is the FORMATION:– A rock body distinguishable from rocks above and

below it– A rock body large enough to be shown on a map

• It may contain one sedimentary facies over a wide area, for example a widespread limestone

• OR it may contain several time related facies: alluvial fan conglomerate, point bar stream deposits, lake mudstones.

Names of rock formationsNames of rock formations Bloomsburg Formation named for

Bloomsburg, Pennsylvania

• “Formation” as second part of name if rock types are diverse

• Correlated with similar rocks in, for example, the Delaware Water Gap area, there called High Falls Formation.

You will hear me call it “High Falls Bloomsburg”

Names of rock formationsNames of rock formations

• Or, a rock formation may be named for a single rock type

• Navajo Sandstone

• Redwall Limestone

Correlation of strata in southwestern United States

Some are named “Formation”Others sandstone (“Ss”) orLimestone (“Ls”)

Subdivision of formationsSubdivision of formations• A formation may be divided into members

• For example, the red “Passaic Formation*” outside can be divided into members, e.g. the Perkasie member, Graters member, etc.

*Formerly called the Brunswick Formation

Groups of FormationsGroups of FormationsTwo or more vertically adjacent formations can be

combined into a group. For example, the Late Triassic and Early Jurassic rocks around here form the Newark Group.

• Included are the Passaic Formation, the Lockatong Formation, the Stockton Sandstone.

• Related groups can be combined into a Supergroup• These formed in a rift valley, eventually flooded, opening

the Atlantic

Role of Tectonic Forces - 1Role of Tectonic Forces - 1

• Uplift may control distribution of sedimentary facies:

• Uplift increases stream gradients and velocity, rate of erosion of sediments into basin. Streams faster, erosion greater.

• Example: Continent-Continent collision

• Causes thick sedimentary clastic wedges

Clastic wedgesClastic wedgesThick and coarse-grained close to source area, thinner and more fine-grained further from source area

Shallow water deposition in a basinShallow water deposition in a basin

Crust deforms as weight increases. Basin floor stays at about the same depth.

Transgression and RegressionTransgression and Regression• Changing sea level greatly influences distribution of depositional facies

• The process of transgression ( rising sea level): the ocean rises and covers the continental margin

• Shoreline moves towards continental interior

Regression: The process of regression produces lowering of sea levelShoreline migrates away from the continental interiorVery useful for correlation – widespread erosion causes unconformities – Sequence Stratigraphy

•Global sea level changes are called eustatic

Eustatic sea-level changes for the Eustatic sea-level changes for the Phanerozoic EonPhanerozoic Eon

Note how often period boundaries correspond to regressions

These same boundaries often correspond to extinctionsREGRESSION exposes shelf

K\T >Regression at boundary

Pm\TR largest >

extinction, no regression, definite

ash layer

Sauk

Tippecanoe

Kaskasia

Absaroka

Long-term sea level changeLong-term sea level change

• They last tens of millions of years

• Controlled by size of MORs

• Warm, active, buoyant ridges displace ocean waters onto continental margins

(transgression)

• Cold, inactive, dense ridges are smaller and basins have more room for water.

(regression)

Rapid sea-floor spreadingRapid sea-floor spreading

Growing MOR takes up basin volume, sea level rises - transgression

Cessation of sea-floor Cessation of sea-floor spreadingspreading

MOR cools and shrinks, sea level drops - regression

Very short Sea-level CyclesVery short Sea-level Cycles

• Associated with growth and shrinkage of ice sheets

• Last hundreds of thousands of years• Result from removal of water by storage

as glacial ice• Exposed much of continental shelf

surrounding North America• Sea level as much as 140 meters lower

than present

Recall Lowered Sea-level –PleistoceneRecall Lowered Sea-level –Pleistocene

Caused exposed shelfLand Bridge

Recall Sediments controlled by EnergyRecall Sediments controlled by Energy

• Sand deposited at shoreline and in adjacent shallow waterHigh Kinetic Energy – surf, longshore drift

• Mud deposited in calm, deeper water

Low Kinetic Energy lakes in winter, lagoons, bays, very deep ocean beneath the surface

Some time-equivalent sedimentsSome time-equivalent sediments

Differ in energy and distance from source

Facies changes with TransgressionFacies changes with Transgression

• Rising sea level = shoreward migration of sedimentary facies

• Deeper water sediment over shallower• Mud facies is superimposed over sandy

beach facies

• Carbonate Ooze facies is superimposed over Mud facies

• “FINE-ING” UPWARD

Effect of transgression on Effect of transgression on sedimentary faciessedimentary facies

Deeper water sediment over shallower (see center block)Mud facies is superimposed over sandy beach faciesCarbonate Ooze facies is superimposed over Mud facies

Note the wedge

RegressionRegression

• Falling sea level causes landward facies to be superimposed on the seaward facies

• Sandy beach facies is superimposed over muddy lagoon facies

• Shallower water sediment (coarse) over deeper (fine)

• COARSENING UPWARD sequence OR a DISCONFORMITY due to “subaerial exposure” i.e. shelf or inland sea sediments were exposed to erosion when sea-level dropped

Coarsening upward sequenceCoarsening upward sequence

Regression: from deepwater to shallow water over any spot

Fine Muds of Mancos Shale

Coarse Sands of Mesa Verde Group

Regression

Walther’s LawWalther’s Law

• Vertical sequences of sedimentary facies result from superposition of laterally adjacent depositional environments.

• Used to recognize changes in sea-level t-r

• Used to recognize neighboring facies

Walther’s LawWalther’s Law

Vertical sequences of sedimentary facies result from superposition of laterally adjacent depositional environments

Transgression fining (deeper) upward

PaleogeographyPaleogeography

• Reconstruction of past landscapesReconstruction of past landscapes

• Example: Asymmetrical stream ripples Example: Asymmetrical stream ripples indicate flow directions of riversindicate flow directions of rivers

• Gives location of high topographyGives location of high topography

• Paleocurrent indicators in delta deposits:Paleocurrent indicators in delta deposits:

Size of ripples and their formSize of ripples and their form

• Continent positions from PaleomagneticsContinent positions from Paleomagnetics

PaleoecologyPaleoecology

• The reconstruction of past ecosystemsThe reconstruction of past ecosystems

• Example:Example:

• Type and thickness of vegetation near Type and thickness of vegetation near pond, oxbow, lake, or floodplain can be pond, oxbow, lake, or floodplain can be determined from fossil leaves and pollen, determined from fossil leaves and pollen, and fossil soil layersand fossil soil layers

• Niche of modern animals can be related to Niche of modern animals can be related to fossil animals similar in skeleton, teeth.fossil animals similar in skeleton, teeth.

SedimentologySedimentology• Interpret sediments deposited in past by

comparison to sediments in modern environments

• Energy decreases with depth• Fine-grained sediment indicates deep water• So: Fining-upward sequence of sediments

indicates decreasing energy (deeper water - Transgression)

• And: Coarsening-upward sequence of sediments indicates increasing energy (shallower water - Regression)

PaleoclimatologyPaleoclimatology

• Certain types of sedimentary rocks are Certain types of sedimentary rocks are good indicators of paleoclimategood indicators of paleoclimate

• Evaporites indicate dry regionsEvaporites indicate dry regions

• Coals indicate swamp conditionsCoals indicate swamp conditions

• Dunes and desert pavement semi-arid Dunes and desert pavement semi-arid to arid regionsto arid regions

• Tillites, striated rock surfaces, loess Tillites, striated rock surfaces, loess etc. record very cold glacial conditionsetc. record very cold glacial conditions

End of Part 1End of Part 1

Importance of FossilsImportance of Fossils

• Many early philosophers (including Aristotle) Many early philosophers (including Aristotle) recognized fossils are remains of ancient liferecognized fossils are remains of ancient life

• Importance of fossils to geology realized Importance of fossils to geology realized laterlater

• Wm. Smith – Mapping in Wales and England Wm. Smith – Mapping in Wales and England developed Principle of faunal successiondeveloped Principle of faunal succession– Different-aged rock layers contained different Different-aged rock layers contained different

fossilsfossils– Allowed formulation of the geologic time scaleAllowed formulation of the geologic time scale

Fossil Wooly MammothPleistocene and Cold

Part 2Part 2

• Mostly Chapter 18

Index fossils vs. Long RangingIndex fossils vs. Long Ranging

Wm. Smith: used fossils to correlate rocks far apart and establish relative age

Short range“index fossil”

Long range useless for correlation

Domains of lifeDomains of lifeJohn Ray (1680) Grouped organisms according to similarity

Carl von Linne’ ,1760, called LinnaeusCarl von Linne’ ,1760, called Linnaeus Binomial Nomenclature Binomial Nomenclature (Genus and species)(Genus and species)

Species based hierarchy of relationships

Similar species grouped together in a Genus (capitalized) each with a unique species name (lower case). Example lion Felis leo, African wild cat Felis silvestris

Note plural of species is species. Plural of genus is genera. Similar genera grouped into families, families into orders, orders into classes, etc. Mnemonic

• Knew of similarities among diverse organisms, Naturalist on Beagle 1831-1836, saw changes in fossils through time.

• Knew of Artificial Selection by farmers

• Was aware of Malthus (1798) essays on population, “more individuals are born than

food supply can support.”

• Read Lyell’s Principles of Geology- supports Hutton’s uniformitarianism/gradual change

• Suggested Natural Selection

Darwin’s RoleDarwin’s Role

http://www.aboutdarwin.com/voyage/voyage01.html

Evidence: Homologous structuresEvidence: Homologous structures

Homology: Same anatomy to make different structures. Why, if not related?

Darwin’s Idea: Natural SelectionDarwin’s Idea: Natural Selection

• Organisms produce more young than 2

• There is competition for food and mates

• There is variation in characteristics (types) essential to survival and reproduction

• Some individuals (types) survive to reproductive age, mate and have progeny more frequently than others. This is “success”.

• “Successful” individuals pass on their characteristics to the next generation

InheritanceInheritanceIndividuals vary, but we look like our parentsHow does variation get passed on?• Jean Baptiste de Lamarck (pub.1801)

– Acquired Traits are inherited - WRONG– Giraffe strains to reach high leaves, offspring

have longer necks – failed idea

• Johann Gregor Mendel (pub.1866) Established rules of inheritance in peas. – Traits controlled by genes – Genetic traits are inherited - RIGHT

http://anthro.palomar.edu/mendel/mendel_1.htm

http://www.ucmp.berkeley.edu/history/lamarck.html

Mendel 1865 -1866Mendel 1865 -1866

Prevailing idea was that the characteristics of an Prevailing idea was that the characteristics of an organism were due to the blending of the traits from organism were due to the blending of the traits from each parent (blending inheritance). each parent (blending inheritance).

Mendel proposed instead that an “element” Mendel proposed instead that an “element” determined a particular characteristic of an organism.determined a particular characteristic of an organism.

Called particulate inheritance. The element (now Called particulate inheritance. The element (now called ‘gene’) is the fundamental unit of heredity.called ‘gene’) is the fundamental unit of heredity.

Mendel’s work was not noticed at the time 1865-66Mendel’s work was not noticed at the time 1865-66 Rediscovered by Hugo deVries, Carl Correns, and Rediscovered by Hugo deVries, Carl Correns, and

Erik von Tschermak in the early 1900’s.Erik von Tschermak in the early 1900’s.

Mendel’s (1865 -1866) DiscoveriesMendel’s (1865 -1866) Discoveries Some physical traits are caused by inheritable particles, Some physical traits are caused by inheritable particles,

now called genesnow called genes May occur in two forms: one is dominant (capital letter, May occur in two forms: one is dominant (capital letter,

e.g. R, the other recessive (lower case letter, e.g. r).e.g. R, the other recessive (lower case letter, e.g. r). Every individual gets two copies of each gene, one from Every individual gets two copies of each gene, one from

each parent. Only need one dominant to get normal each parent. Only need one dominant to get normal appearance.appearance.

Ex: Pea flower color, normal is RedEx: Pea flower color, normal is Red Can get RR, Rr, rR, (all red) or rr (white)Can get RR, Rr, rR, (all red) or rr (white) Double recessive rr red gene is broken, no red, flower Double recessive rr red gene is broken, no red, flower

whitewhite

Mendel’s experiments with peasMendel’s experiments with peasFlower color

Some traits (flower color)occur in two forms. One (Red flower R) is dominant.The other (white r) is recessiveFirst generation all Rr

If Red (R) and white (r) parents 3/4 of next generation are Red (dominant)

Parents

1/4 1/4

1/4 + 1/4 = 1/2

Suppose you cross a RR plant with a white plant

Where are the genes?Where are the genes?

• Early 1900s growing suspicion that the inheritance material is in the chromosomes

• Evidence from microscope studies of cell division (Mitosis) versus gamete formation (Meiosis)

Mitosis – cell divisionMitosis – cell division

Two copies of each per cell.One from mother, one from father. Diploid

In Mitosis (cell division) the chromosomes duplicate and separate, then the cell divides, so each daughter cell again has 2 pairs of chrosomes.

But in Meiosis – formation of gametes:But in Meiosis – formation of gametes:

But in Meiosis, gamete formation, an extra division makes cells with one copy of each chromosome, so many possible combinations

Each gamete has, for each chromosome, either version, not both

Sexual reproductionSexual reproduction

One from each parent

How does the genetic material make copies?

Chromosomes contain lots of DNA deoxyribose nucleic acid

Chargaff’’s Rules on DNA components weighed nucleotides

The amount of Guanine (G) equals Cytosine (C) The amount of Adenine (A) equals Thymine (T) Adenine and Guanine are Purines,Thymine and

Cytocine are Pyrimidines

How does the genetic material make copies?

Francis Crick, James Watson (models) Maurice Wilkins, Rosalind Franklin (x-rays) of DNA The Double Helix by James Watson

http://www.pbs.org/wgbh/nova/photo51/

DNA moleculeDNA molecule

Francis Crick, James Watson, Maurice Wilkins, Rosalind Franklin

It has not escaped our notice …It has not escaped our notice …

• Chargaff’s Rules make sense immediately

• Cytosine only fits Guanine (3 H bonds)

• Thymine only fits Adenine (2 H bonds)

• They will bond only to each other, making a perfect copy on the opposite strand

• Parents can pass a copy of their DNA in their gametes

Breaking the Genetic CodeBreaking the Genetic Code

• RNA

• The genetic code UUU (Uracils) => Phenylalanine

• One gene, one polypeptide chain, enzymes

Marshall Warren Nirenberg

Speciation – Geographic IsolationSpeciation – Geographic Isolation

Separated – populations eventually unable to interbreed - definition of “distinct species”