What’s the oldest thing you

have ever touched?

Evolution of Landforms and

OrganismsContinued – Part Two

Geology – Study of the Earth

Geologic Terms

Chemical Weathering

Mechanical Weathering

Age of Earth

Absolute dating Trilobite Age of rocks

Relative dating Ice core Fossils

Radioactive dating Index Fossils Eons

Law of superposition

Geological Time Scale

Eras –Periods -Epochs

Unconformity

Age of Earth?thousands - millions - billions trillions

4.6BillionYears

old

How is the Age of the Earth Determined?

Relative AgeAbsolute Age

Relative Age or Absolute Age“No Ordinary Family”

Absolute Age and Rocks• Absolute age tells the actual age of a rock. • Radioactive Decay or Radiometric Dating is one

method that gives the age of a rock by comparing the amount of radioactive material in the rock with the amount that has decayed

Parent Isotope Stable Daughter Product Currently Accepted Half-Life Values

Uranium-238 Lead-206 4.5 billion years

Uranium-235 Lead-207 704 million years

Thorium-232 Lead-208 14.0 billion years

Rubidium-87 Strontium-87 48.8 billion years

Potassium-40 Argon-40 1.25 billion years

Samarium-147 Neodymium-143 106 billion years

Radioactive Dating - Carbon Dating• The half-life of a radioactive

element is the time it takes for half of its atoms to decay into something else.

• For example, the half-life of radium-226 is 1600

• Therefore, in 1600 years, one gram of radium-226 will turn into half a gram of radium-226 and half a gram of something else

• After another 1600 years have elapsed, only a quarter of a gram of the original radium-226 will remain.

• Finding the ratio of parent to daughter elements

• Carbon-14 is an isotope that has a half life of 5,700 year old.

• Half-life – The time it takes for half of the atoms in an isotope to decay

• Radiometric Decay – Process that uses properties of atoms in rocks and other objects to determine their ages.

• Radioactive Dating – calculating the absolute age of a rock by measuring the amounts of parent and daughter materials in a rock and by knowing the half-life of the parent material

Every living thing contains Carbon -14• It has been used to date

fossils such as frozen mammoths, pre-historic humans, plants and animals that lived up to about 50,000 years ago.

• It’s half-life is only 5,700 years so it can’t be used to date ancient fossils or rocks.

Carbon dating tells when this mammoth died

Elements Used in Radioactive DatingRadioactive

ElementHalf-Life (years)

Dating Range (years)

Carbon –14 5,770 500-50,000 Potassium – 40 1.3 billion 50,000-4.6 billionRubidium –87 48.8 billion 10 mill – 4.6 billThorium – 232 14 billion 10 mill – 4.6 billUranium – 235 713 million 10 mill – 4.6 billUranium – 238 4.5 billion 10 mill – 4.6 bill

Calculating Half Life• Carbon-14 decreases by half every 5,700 years. • A sample of 1g of carbon-14 will decrease by half to

0.5 after 5,700 years• How much carbon-14 will there be in 17,100 years?

a. 0.125 gb. 0.8 gc. 0.1 gd. 0.025 g

5,700 is 3 times more than 17,100

1.Divide 5,700 / 17,100 = 32.1g X 0.5 = 0.53.0.5 X 0.5 = 0.254.0.25 x 0.5 = 0.125g

Determining the Absolute Age of Rock LayersRadioactive Dating

A technique for measuring the age of an object or sample of material by determining the ratio of the concentration of a radioisotope to that of a stable isotope in it; for example, the ratio of carbon-14 to carbon-12 reveals the approximate age of bones, pieces of wood, and other archeological specimens.

Blocks

Which block is the oldest ?Which block is thy youngest?

• Stack the blocks • Do not stack according to size

Law of Superposition• In undisturbed

sedimentary ROCK, the oldest layers are deeper down, at the bottom and the youngest layers are closer to the top.

• Kids are younger & come after parents & grandparents.

• Kids• Parents

• Grandparents

• Great-grandparents

Law of Superposition – Rock Layers• This law states that if a rock

layer has not been disturbed then;– Older layers of rock lie

beneath younger rock layers

– This should make sense• The oldest sediments

must be laid down before the younger ones can pile up on top.

Rock Layers

Blocks

Which block is the oldest ?Which block is thy youngest?

• Tilt the blocks to at an angle.• What happens to the rock layers

when they are tilted?

Blocks

Which block is the oldest ?Which block is thy youngest?

• Continue tilting the blocks until the layers have reversed positions.

• Now….

Unconformity• Plate movements can fold, tilt or turn rock layers

• An unconformity is a “missing” rock layer• This sometimes makes it difficult to age rock

layers• An unconformity is a buried erosion surface separating

two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval of time before deposition of the younger, but the term is used to describe any break in the sedimentary geologic record.

UnconformityIgneous or metamorphic rock is a nonconformity. The boundary

represents a nonconformity. Igneous or metamorphic rock may be uplifted to Earth’s surface by crustal movements. Once the rock is

exposed, it erodes. Sediments are deposited on the eroded surface.

Angular UnconformityThe most obvious kind is the angular

unconformity. Rocks below the unconformity are

tilted and sheared off, and rocks above it are level. The angular unconformity tells a clear story:

• First a set of rocks was laid down.• Then these rocks were tilted, then

eroded down to a level surface.• Then a younger set of rocks was laid

down on top.

Angular UnconformityAn angular unconformity forms when rock deposited in horizontal layers is folded or tilted and then eroded. When erosion stops, a new horizontal layer is deposited on top of a tilted layer. When the bedding planes of the older rock layers are not parallel to those of the younger rock layers deposited above them, an angular unconformity results.

Water Causes Mechanical and Chemical Weathering

Iron oxidation

water expands when it freezes

Chemical WeatheringThe main agent of chemical weathering is

WATER

Rocks react with water, gases and solutions(may be acidic); will add or remove elementsfrom minerals.

Why is the Statue of Liberty Green?

The statue is made of copper. Copper is naturally the color of a shiny penny. But, when copper is exposed to rain it tarnishes. This is chemical weathering. The rain contains copper carbonate, maybe sulfuric acid which gives it the green color. It turns the statue into copper oxide and other elements due to “oxidation”.

Mechanical Weathering• Thermal expansion – heating and cooling of rocks

– heat causes expansion; cooling causes contraction.

• Freezeing –Thawing action of water in the cracks of rocks

water expands when it freezes

Mechanical Weathering• Animals can

burrow beneath the ground and break up rocks and soil

• Plant roots can grow and crack and break up rocks and soil

The salts in our oceans is a result of weathering of rocks and soil.

• One way minerals and salts are deposited into the oceans is from outflow from rivers, which drain the landscape, thus causing the oceans to be salty.

Rain contains some dissolved carbon dioxide from the surrounding air. This causes it to be slightly acidic. The rain physically erodes the rock and the acids chemically break down the rocks and carries salts and minerals into the oceans

Weathering Created the Grand Canyon

Ice Cores• Studying ice cores helps in• understanding how climate has

changed - warmer and/or colder• Ice forms layers similar to rock

layers • We have also learned about the Ice

Ages by discovering fossils that are missing in rock layers.

• The layers record amounts of gases and elements present in the atmosphere and water at a particular time in history

Ice Core

PaleontologistsPaleontologists study fossils theyfind embedded in “sedimentary”rocks. They use the informationto determine what the earth and life was like in the past.The fossil record explains aboutlife in the past and how it andthe environment has changed over time.

The rest of ANSWER # 17 is on another slide - Put your pencil down

Fossils are our window to the past. They show us what life was like millions of years ago.

FossilsThey are evidence of once-living things.They show how species have changedover time and how some species are related to one another.

Fossils can give us evidence of past lifeFossils suggest that birds evolved from dinosaurs.

A fossil is a rock!

• Most fossils are formed of sedimentary rock.

• They are formed by compacting and cementing together layered sediments.

Most Fossils form in What Kind of Rock ?• Layer upon layer of

sand, mud, dead plants and animals and other small pieces build up and their weight compacts and cements the layers together.

Fossils form Slowly• It takes

about 1 million years to form a sedimentary fossil.

Deposition + Time + Erosion =

Fossils

ANSWERS for # 17 - Fossils Facts• They give us evidence of past life• Most fossils are found in sedimentary rocks• Fossils form slowly• Only the hard parts of an organism is preserved• An organism has to be buried quickly in order to

become fossilized.• They give us clues about the size, shape, growth

patterns and structures of extinct organisms.• They show us how organisms have changed over

time• They show us how organisms are related to one

another.

Preserved Tracks • Tracks give us evidence of the size, weight

and stride of the animal. If several tracks are found that can be evidence of lifestyle: social grouping an interactions among species.

Here’s the Story!• Sometime between 200 and 205 million years

ago a meat eating Eubrontes dinosaur crouched on the shore of lake Dixie. Perhaps it had been eating fish in the nearby deep water. The dinosaur may have been a Dilophosaurus weighing around 1,000 pounds, measuring 6 feet high at the hip and 18 feet long. He sat down leaving the imprint of his feet, heel, pelvis, hands, and tail in the sand. In the process of getting up he shuffled his feet, leaving a second set of impressions. He arose and walked away. For some reason his impressions were buried waiting to be discovered at a later date.

Here’s the

Proof!

Index Fossils• Some species inhabited Earth for

long periods of time without changing.

• INDEX FOSSILS existed for short periods of time, were abundant and were found in lots of different places on Earth.

• Index Fossils have been found in many places throughout the Earth and geologists use them to date the age of rock layers.

Sea Urchin

Ammonite

Ammonites are excellent index fossils, and it is often possible to link the rock layer in which they are found to specific geologic time periods

Geologic Time Scale

Geologic Time ScaleA timeline that organizes the events in Earth’s history.The divisions are based on organisms that existed during that time period and the geologic events that occurred: mountains forming, seas rising, plains forming, etc…

Eon Era Period EpochLargest amount of time in Earth’s history

Pre-CambrianEarly Life

Time when specific animals and plants evolved

Time when specific animals and plants evolved

Lasted billions of years

Paleozoic Age of Fishes

Time when specific mountain ranges were formed

Time when specific mountain ranges were formed

Life evolves MesozoicAge of Reptiles

Example: Jurassic Period

CenozoicAge of Mammals

Organismsthat

existedduring

the CenozoicMesozoicPaleozoic

Eras

Organismsthat

existedduring

the CenozoicMesozoicPaleozoic

Eras

Age of Mammals

Age of Reptiles

Age of Fishes

Quiz

Question 1• Radiometric dating was used in a lab.

What was the scientist investigating?

• Relative age of rocks• Absolute age of rocks• How climate had changed over time• What fossils the rock layer contained

Answer: Absolute age of rocks

Question 2Which of the following would not be a factor in the formation of a fossil?

a.Earthquakesb.Hurricanec.Avalanched.Forest Fire

Answer: Earthquake

Answer:

Question 4• What type of rock are fossils most

commonly found in?• a. igneous• b. metamophic• c. sedimentary• d. rocky or muddy

Answer: Sedimentary

Question 5According to rock records, the Earth is about how old?

a. 4.6 million years oldb. 4.5 billion years oldc. 5.4 million years oldd. 5.6 billion years old

Answer: 4.6 Billion Years Old

Answer: 4.6 billion years old

Question 6A paleontologists discovers a gap of about 2 million years in the rock

layer he is investigating and records this as being…a. An extinction of several fossilsb. Proof of plate tectonicsc. Evidence of volcanic eruptionsd. An unconformity

Answer: Unconformity

Answer: Unconformity

Questions 7 & 8 and 9Could using the half-life of carbon-14 be usedAs a means of dating dinosaurs?

Answer: NONormally, the youngest layer of rock in a rocklayer will be where?

Answer: On the topWhat proof supports this evidence?

Answer: The Law of Superposition

Answer: Relative Age

Questions 10 plusWhat “calendar” shows the history of the Earth?

Answer: Geologic Time ScaleWhat is the main factor that makes each divisiondifferent from one another?

Answer: The organisms that existedWhat is the longest division of time?

Answer: EonWhat is the order of the divisions of time?

Answer: Eon – Era- Period - Epoch

The End

Types of FossilsNot part of 8th grade EOG test

There are 6 basic types of fossils– Cast– Mold– Imprint– Trace– Petrification– Whole Preservation

• Freezing Tar Pits• Peat Bogs Mummification• Amber

Cast

• The fossil formed by filling the shaped space left in rock by a dissolved plant or animal.

• You can think of this as the shape of the jello when it comes out of the mold.

Mold

• A mold is the empty space fossil formed in the outward shape of the dead plant or animal.

• A mold is a shaped hole.

Imprint

• An imprint fossil forms when thin objects like leaves and minnows become trapped in fine mud and make impressions that harden into stone.

Trace

• A trace fossil results from animal or plant activity, such as tracks, trails, burrows or roots.

• These fill with mud that takes their shape and then it hardens into stone.

Petrification

• A petrification fossil is the most detailed type.

• It is the process by which living things are copy-replaced by dissolved minerals. Detail down to the cell level can be seen.

• They have “inside detail”.

Whole Preservation

• Whole preservation is the rarest fossil.

• The entire body of a plant or animal, including the soft parts, is preserved.

• Frozen mammoths, mummies, bog people, tar pit tigers and amber are examples.

Unconformity