Geologic history academic

Geologic History

F SSILS

WHAT ARE FOSSILS?

the remains or trace of a once the remains or trace of a once living thing, usually preserved in living thing, usually preserved in

sedimentary rocksedimentary rock

F SSILS- How are they formed?

ALIVE

F SSILS

DEAD ANDDECAYING

F SSILS

HARD PARTSLEFT BEHIND

Hard parts are the bonesor the shells of an organism

F SSILS

BURIAL ANDFOSSILIZATION

FOSSILIZATION OCCURS WHENMINERALS REPLACEANY ORGANIC MATERIALTURNING IT INTO A FOSSIL (ROCK)

F SSILS

FOSSIL

F SSILSTYPES OF FOSSILS

IMPRINTS

Occur when leaves andOccur when leaves and

feathers leave an feathers leave an

impression in mud that impression in mud that

later hardens into rock.later hardens into rock.


ORGANISMS GET TRAPPEDIN HARDENING TREE SAPAND ARE PRESERVED ASFOSSILS

AMBER


ICE

SOME ORGANISMSMAY BE PRESERVED ASFOSSILS IN ICE


TAR

ANIMALS GET TRAPPED IN TAR PITS AND THEIR REMAINS GET PRESERVED- LA BREA TAR PITS INCALIFORNIA


PETRIFIED WOOD

PETRIFICATION OCCURSWHEN MINERALSDISSOLVED IN GROUNDWATER GRADUALLYREPLACE THE ORIGINALTISSUES OF PLANTS ANDANIMALS

F SSILSWHAT DO FOSSILS TELL US?

APPEARANCEAND ACTIVITIESOF PAST LIFE

FOSSIL TEETH GIVEUS CLUES AS TOWHAT THE ANIMALATE


SPECIES HASEVOLVED ORCHANGED


EARTH’S PASTCLIMATES

NYS

458 MILLION YEARS AGO 250 MILLION YEARS AGO

FOSSIL CORAL = WARM CLIMATE

GE LOGIC TIME

The geologic time scale is based on the

FOSSIL RECORD

LARGETIME

UNITS

SMALLTIME

UNITS

EON

ERA

PERIOD

EPOCH

GE LOGIC TIME

Geologic History of NYS- ESRT p. 8 & 9

Precambrian Eon

Archean Proterozoic

Phanerozoic Eon

GE LOGIC TIME

Geologic History of NYS- ESRT p. 8 & 9

Precambrian Eon

Archean Proterozoic

Phanerozoic Eon

Cenozoic Era Mesozoic Paleozoic

GE LOGIC TIME

Phanerozoic Eon

Cenozoic Era

Quarternary

Period

Mesozoic Paleozoic

Neogene Paleogene

GE LOGIC TIME

Cenozoic Era

Quarternay

Period

EARLY LIFE ON EARTH

Neogene Paleogene

Pleistocene Holocene

GE LOGIC TIMEGE LOGIC TIMEWhy are the sections of geologic time separated

this way?

Major Extinctions Major Climate

Change

Appearance Of new

life

GE LOGIC TIME- Model of Geologic Time

Scale

Name of Era/Eon Millions of Years Ago

Duration Percent of Earth’s History

Cenozoic

Mesozoic

Paleozoic

Precambrian

0 to 65

65 to 251

251 to 544

544 to 4600

65 my

186 my

293 my

4056 my

1.4%

4%

6.4%

88.1%

RELATIVE DATING

What is relative dating?

Determining the age of something compared to

something else

NO NUMBER IS NEEDED!!THIS IS JUST LIKESAYING:

Trilobites are olderthan dinosaurs

Dinosaurs are olderthan mastodonts

We do this to determine howold rock layers are…

RELATIVE DATING

Rules for

Sequencing:LAW OF SUPERPOSITION:

In undisturbed sedimentary rock the oldest layer is on the bottom, youngest on

topYOUNGEST

OLDEST

RELATIVE DATING

Rules for

Sequencing:

FAULTING:

A fault is younger than the layers it

cuts across

Duh!!! Don’t the rock layers need to be therein the first place?

RELATIVE DATING

Rules for

Sequencing:

IGNEOUS INTRUSION:

An igneous intrusion is younger than the

rock layers it penetrates

Remember igneous rocks form from magma. An igneous intrusion is when magma seeps up in between rock layersand hardens to form rock.

RELATIVE DATING

Rules for

Sequencing:

CONTACT METAMORPHISM:

The contact metamorphism is younger than the

layers it cuts through

When the magma seeps up between rock layers it is very hot and it bakes the rocks around it. The surrounding rocks do not melt but are metamorphosed.

Duh again!!!! If there were no rock layers there then there wouldn’t be anything to turn into metamorphic rock.

RELATIVE DATING

Rules for

Sequencing:

Unconformity

A “missing” layer of rock. buried erosional surface.

Rocks were deposited, erosion occurred at the surface and then new rock was deposited.

RELATIVE DATING

Rules for

Sequencing:

TILTING:

Tilting or folding of rock layers is

younger than the layers it affects

Relative Dating Instructions

Relative Time:Ages of events are placed in order of

occurrence.

No exact date is identified. Ex. WWI and WWII

"I am the second child in my family."

Law of Uniformitarianism

• "The present is the key to the past."

• or what we see now has almost certainly happened before and therefore can be used for interpreting the past.

Original Horizontality- Rocks are usually deposited flat and level.

• You would say– “Deposition of”

sandstone, limestone, shale, etc.

– This applies to sedimentary rocks ONLY

The law of cross-cutting relationships—an igneous rock is younger than the rocks that it has intruded into. This also applies to faults.

You would say— “Igneous intrusion” or faulting/folding.

4. Faulting3. Deposition of Shale2. Deposition of Sandstone1. Deposition of Limestone

Sequence 1: Uplift & Erosion

• Any time folding or tilting occurs• UPLIFT will occur• If there is uplift – EROSION will

occur

Unconformity

• A “gap” in the rock record where erosion or non-deposition occurred.

• You must include this as a separate step in the sequence of events.

•Layers are formed according to superposition.

Here’s How It Works!Here’s How It Works!

•Something happens to uplift the area- (folding, faulting, etc).

•Erosion wears away the uppermost layers

•Area submerges (or sinks) and deposition begins again.

Other Guidelines for figuring out a sequence:

• Sedimentary rocks are usually formed under water.

• Weathering and erosion usually happen above water (on dry land).

Practice Sequencing

• Turn to page 7 in your notes.

• We will complete #1 together.

• Complete #2-#6 for homework, we will go over them tomorrow.

Practice Sequencing #3

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Rock Correlation

• Want to know what happened in Earth history in widely different locations?

• Rock correlation -- hooks up rocks that look alike

– The key bed – a particular strata that is very distinctive

– Fossil correlation -- hooks up rocks that formed at the same time and relies on the following:

• index fossils • Rock type (color and composition)

Rock Correlation:

Matching up outcrops at different locations

Volcanic TimeMarkers

Index Fossils

Rock layers have:Same color, and

composition

Outcrop 1 Outcrop 2 Outcrop 3 Outcrop 4

Correlating Rock Layers

Index Fossils

Short Lived

Wide Spread

Absolute Age

Examples

--65 Million Years Ago --1990

What is absolute age?

Identifies the exact date of an event

How can we figure it out?

Radio Active decay

Radioactive(parent element):

Atom with anunstable nucleus

that decays

Radioactive(parent element):

Atom with anunstable nucleus

that decays

Carbon 14: CarbonDating

Used to date organic remains(woods, bones) no older than

50,000 years

Half-Life:

Time it takes for ½ of a radioactive element

to decay into a stableelement

Is NOT affected by:

Heat Pressure

Mass

Daughter Element:

Stable element, productof radioactive decay

Technology

Geologic history academic