Geologic History

This unit will help you develop an

understanding of the history of our planet

Formation of the UniverseBig Bang Theory—the most accepted scientific theory of the origin of the universe

Def.: Theory that the whole universe began as a dense mass that exploded and expanded outward approximately 13-15 billion years ago

* Still expanding today!!!

* All the gases and dust from the explosion formed everything in the universe

• The Earth is about 4.5 billion years old. That means that approximately 9 billion years went by between the formation of the universe and the formation of the Earth!!!!

Earth began as a big mass of molten material that gradually cooled and hardened

The constant volcanic eruptions gave off a great deal of gas

Outgassing produces early atmosphere consisting of:

• Carbon dioxide

• Hydrogen• Helium• Ammonia • Methane• Sulfur Dioxide• Others

Eventually an atmosphere did form and the gases formed clouds and rain (liquid versions of the chemicals listed earlier) began to fall (cooling the hot planet) and made oceans.

Earth was being bombarded with meteorites too!! One was big enough to cause part of the molten Earth to “splash” off and form the moon—and it was really close to us! It has slowly moved farther away

Microscopic organisms (bacteria) evolved in the oceans 4.1 billion years ago

These organisms eventually evolved the ability to perform photosynthesis (converting sunlight and carbon dioxide into food and giving off oxygen as a waste product)

Cyanobacteria3 billion years ago

Microscopic organisms (bacteria) evolved in the oceans

These organisms evolved the ability to perform photosynthesis (converting sunlight and carbon dioxide into food and giving off oxygen as a waste product)

Colonies of Cyanobacteria are called STROMATOLITES. Fossilized stromatolites have

been found all over the world

Photosynthesis

A few billion years of evolution produced plants and other organisms that turn carbon dioxide into

oxygen through photosynthesis.

Carbon Dioxide

Oxygen

CO2 + sunlight energy (food for plant) + oxygen

This new oxygen production changed our atmosphere and harsh environment into the

earth we live in today!

Geologic Time ScaleMainly on the basis of fossil evidence, geologists have been able to break down geologic time into divisions.

Use the ESRT!!! There is A TON of information crammed onto pages 8 & 9

Also…you must remember that MOST sedimentary rocks form in the water and that MOST invertebrate organisms lived in the water

Fossil -the remains or evidence of something once living

Evolution—by studying fossils, paleontologists (scientists who study fossils) make observations, finding patterns in life forms and theorize that organisms have changed throughout geologic history

Evolution—by studying fossils, paleontologists (scientists who study fossils) make observations, finding patterns in life forms and theorize that organisms have changed throughout geologic history

Sweet Video – A Brief History of Life on Earth

How much time is represented by each of these little boxes?

100 million years

How much time is represented by each of these larger boxes?

500 million years

Tells us how long ago all the events on this timeline occurred.

How long ago was 4600 mya?

4,600 million years ago How many zeroes in a million?

4,600,000,000 years ago

PrecambrianMajority of time on Earth

4,600 - 542 = 4,058 myamya = millions of years

ago

Earth’s beginning

or 4,058,000,000 years

88% of Earth’s history!

What part of the Precambrian is when the oceanic oxygen first entered the atmosphere?Early Proterozoic

The oldest known rocks are from what time period?

Early Archean or early Precambrian

IMPORTANT:

The timeline on the left side of this line is VERY different from the time line on the right side of this line. Please make this line extra dark and bold in your ESRT!!!

Lasted from 542 mya to 251 mya

Indicates the beginning of the Cambrian period

Indicates the end of

the Cambrian

period

The next column (EPOCH) breaks periods down into smaller frames of time.

Cenozoic epochs have names whereas the rest are referred to as early, middle and late.

If it is early in a period does that mean it is the beginning or the end?

Between Epoch and Life on Earth, there is an ENLARGED timeline for you.

The next column gives you an idea of the plants and animals present on earth during each time period.

During which time period were the earliest birds?

Late Jurassic

Bar indicates that there is a complete sediment record for the Quaternary period.

In the Neogene, no bar indicates that there is a missing sediment record. Perhaps sediments never formed OR erosion took place.

Further down the chart the symbol changes to the rock record. Bar indicates that there is a rock record for the END of the Triassic period and the BEGINNING of the Jurassic period.

This next section gives a bar graph of different groups of fossils.

How many periods could you find trilobite fossils from?

About 7

The letters match the pictures at the

bottom of your ESRT.

Where you find the letter on the bar helps you to find the period it

lived.

Just remember that the globes shown here do not go across horizontally!! You must follow the arrows.

Reading the Important Geologic Events in NY column is similar to reading the other columns. Look for what you need then read horizontally across the ESRT to find the information you are looking for (period, era, epoch, or mya).

Time to color your ESRT!

Evolution—by studying fossils, paleontologists (scientists who study fossils) make observations, finding patterns in life forms and theorize that organisms have changed throughout geologic history

Who Dunit?

Relative Dating Vs. Absolute Dating

Relative Dating refers to the determination of age compared to other events.

Absolute Dating refers to determining the actual age of something in years.

Put these pictures into chronological sequence:

oldest

youngest

What you have just done is relative dating! Of course, it’s a little bit more difficult than that for a geologist.

Uniformitarianism—

”the present is the key to the past”—the theory that the geologic processes that are occurring today occurred in the same way in the past.

Law of Superposition—the oldest rocks are deposited first

Youngest rock layer

Oldest rock layer

(Think: laundry basket!)

Before we learn about the third law, we need review some vocabulary!

Fold—when rock layers are bent/deformed due to tectonic stress (such as plate collisions)

Fault—a crack or break in the rocks along which movement has occurred

Intrusion—when magma cuts through rock, causing contact metamorphism of the pre-existing rock

Extrusion—when magma (lava) cuts through rock and reaches the surface, causing contact metamorphism of the pre-existing rock

“Bent” rock layers are a fold

Intrusion of igneous rock

Fault

Vocabulary Review

Law of Crosscutting Relationships—the rocks were there first before anything altered the rock (such as an intrusion, extrusion, fold, or fault)

Older

Intrusion is younger

Rocks are older

Fault is younger

Using the two laws you just learned, sequence these rocks. #1 is the oldest.

1234

5 is fault XY

6

Law of Included Fragments—the sediments within the rock are older than the rock itself.

Older than the whole rock

Unconformity—a buried erosional surface

unconformity

http://www.classzone.com/books/earth_science/terc/content/visualizations/es2902/es2902page01.cfm?chapter_no=visualization

Unconformity—a buried erosional surface

Deposition of sediments that form rocks

Uplift of the rock out of the water

Erosion

Subsidence—the land sank OR sea level rose so that new rocks could form (repeating the cycle again)

unconformity

Unconformities form by

It is time to practice the laws of geologic history!!

Correlation—matching rocks or geologic events from different places

This is important to figure out the geologic events of an area and locating mineral resources. Important for telling the whole story.

This can be done by:a.) Index Fossils (see next slide)

b.) Volcanic Ash Layers (each volcanic eruption is unique and the chemical properties of the ash are different)

c.) Meteorite Deposits (every impact is different and the composition of the meteorites, asteroids or comets is also different and the chemical properties of the debris can be studied)

Sweet Video

Index Fossil—the fossil remains of an organism that:

1.) lived over a wide geographical area (giving the fossil a large horizontal distribution in the bedrock)

2.) lived for a relatively short period of time (giving the fossil a small vertical distribution in the bedrock)

MEMORIZE THESE

Which fossil could be used as an index fossil?

This fossil can only be found in one layer (small vertical distribution) and can be found in all 4 locations (large geographic distribution)

This one is found in all 4 locations

This one is found in too many layers of rock

STUDY FOR TEST!

Test covers :ESRT pages 8 & 9Evolution of the Earth

(how planet transformed into the one we have today)

LAWS! (Superposition, Crosscutting, Included fragments)

Correlation Index Fossils

What is the difference between relative dating and absolute dating?

Absolute Dating (exact age)

Radioactive Decay—an unstable atom releases particles and electromagnetic energy thus changing into atoms of other isotopes and elements

Isotope: Atoms with the same number of protons, but differing numbers of neutrons.

Isotopes are different forms of a single element.

Radioactive decay can be used during radioactive dating to determine the age of a rock or fossil

http://science.discovery.com/videos/100-greatest-discoveries-shorts-radiometric-dating.html

Half-life—the time required for half of the atoms in a given mass of an isotope to decay.

Half life is not affected by environmental factors such as temperature, pressure, or chemical reactions

Parent isotope is unstable and changes into the stable daughter product

A list of isotopes is found on page 1 of the ESRT

Used for dating:• carbon 14 - Fossil wood, shell, bone, fabric and ash between 1,000

and 70,000 years old.

• potassium 40 – certain minerals more than 100,000 years old

• uranium 238 -Uranium ores and granitic rocks more than 10 million years old.

• rubidium 87 - Some granitic rocks, sandstones, igneous, sedimentary and metamorphic rocks more than 10 million years old.

When an animal first died, it contains all of the Carbon-14 it will ever have (100%). Then after one half life, or ____________ years…

100% Carbon-14

Key: = C-14

Hint: Use ESRT pg 1

After one half life, or 5,700 years—use ESRT page 1, there will be 50% C-14 and the rest of the C-14 will decay into Nitrogen-14.

100% Carbon-14

50% C-14

and

50% N-14

Key: = C-14 and = N-14

1 half-life

After a second half life, or a total of 11,400 years, there will now be 25% C-14 (cut it in half again) and then N-14 will increase to 75%.

100% Carbon-14

50% C-14 and

50% N-14

Key: = C-14 and = N-14

25% C-14 and

75% N-14

1 half-life 1 half-life

If this process continues, will there ever be 0% C-14 and 100% N-14?

Radioactive decay will continue for a long time, but the numbers will keep getting smaller and smaller & eventually will become so small that it will be too hard for scientists to measure.

No, because you cannot divide a number in half to get zero.

unstable stable

Half-life

Percent parent vs. daughter

grams # of years

fractions

You have to know the half life before you can figure out the rest!

A paleontologist finds a fossilized bone and wants to determine the age of the bone. After further studies, he discovers that the bone contains 1/8 C14 and 7/8 N14.How many half-lives have gone by?

How old is the bone? Use the ESRT to

determine the half-life of Carbon-14.

A paleontologist finds a fossilized Elliptocephala and wants to determine the age of the bone.

Should the paleontologist use Carbon-14? Why or why not?

Using radioactive decay, a bone has been dated to be 388 million years old.

Which geologic period is this bone from?

Which geologic era?

Which animal(s) could this bone belong to?

Devonian

Paleozoic

Fish, amphibian, ammonoids, or sharks