8 th Grade Science Name: _______________________________________Geologic History Guided Notes - Uddo

I. FossilsFossils - preserved ___________________ __________ _______________ of living things, found in sedimentary rock **For fossil to form we the organism NEEDS to have __________________ ________________ ex. ________________, __________________, teeth, seeds woody stems

How does this process work?1.) The organism _________________2.) It is ___________________ by sediment3.) The sediment hardens into _________________ and preserves the ________________ of the organism4.) _________________, weathering and erosion _______________the fossil

**Many organisms that become ___________ live in or near quiet _____________ (___________, lakes or shallow seas)

Draw a diagram in the box below illustrating the process of fossil formation

Types of Fossils• Molds and Casts (most common)

• Molds -_______________ area in sediment in the shape of an organism, organism is buried then decays

• Cast -solid _______________ of the shape of an organism, formed when water deposits minerals in a mold

Mold Cast • Trace Fossils- provide _____________ of the _____________ of ancient organisms

• ex. ___________________, trails, burrows, ________________, eggs and nests, burrows• Preserved Remains-

• Sticky ______________• Tree resin produces ____________ (hardened tree sap) which traps organisms **Think Jurassic Park• ____________________

Fossils help explain Earth’s History• Show how life _______________________ over time• Show how Earth’s ____________________ has changed

• Marine fossils found on the top of ________________________• Show how _______________________ has changed

• ___________________ ___________________ fossils found in northern part of US• Show how ______________ _______ ______________ of past life has changed

• __________________ give clues to what animals ate• Bones give clues to how animals ___________________

II. Relative DatingRelative Age-__________________________________________________________________________________________________ Principle of Uniformitarianism- ____________________________________________________________________________________________________________________________________________________________________________________

***Think about people who wear a uniform – nurses, students, police officers à they all look the__________

Law of superposition -____________________________________________________________________________________________________________________________________________________________________________________

**More simply—the oldest layer is on the ____________ and the ____________ is on the top

Draw a picture illustrating the principal and law below below:

Index Fossils- layers with matching ____________________ fossils are the __________________ age

To be an index fossil, the species must 1.) Be geographically _________________________2.)__________________ for a _________________ period of geologic time

Principle of Original Horizontality- __________________________________________________________________________________________________________________________________________________________• Sedimentary rocks NOT in _________________ _________________ have been altered after they

were deposited.

Anything that disturbs sedimentary rock layers, has to be __________________than the layers it affects

o Disturbances include: _____________________________ _____________________________ _____________________________ _____________________________

• This means that if rocks are tilted or folded, they have been deformed ___________ deposition

Principle of Cross Cutting Relations- ____________________________________________________________________________________________________________________________________________________________________________________

Fault- a _________________ in Earth’s crust due to forces inside Earth which causes movement of the rock on opposite

A fault is ALWAYS ________________ than the rock that it cuts through

Folding- sedimentary rock layers are bent ____________ or downwards from their original ______________ position

Folding is __________________ that the youngest rock affected Sometimes forces inside Earth fold layers so much that the layers are

over turnedo The youngest layers might end up on the bottom

Extrusion - lava that hardens on _____________ ____________ and forms igneous rock

Intrusion-magma that pushes into rock layers and cools as igneous rock _____________ ____________ surface

Contact Metamorphism: Occurs when magma (an intrusion or extrusion) ____________ and heats up existing rock layers. This alters the rock into _______________ _____________.

**Represented by __________ marks around intrusion/extrusion.

Draw a diagram of an intrusion and extrusion, draw and label the contact metamorphism

Unconformity-_________________________________________________________________ **It is represented by _____________ ____________ • When rock layers ______________ away, an older rock surface may exposed, they may

erode then _____________________ begins again building new rock layers **Due to __________________, most of the geologic rock layers and _______________ in them has been lost

Procedure A:Using cross sections below determine the sequence of events and order them from oldest to most recent. In addition to determining the relative age of the different strata, you need to determine the relative age of unconformities (erosion), cross-cuttings (faults), and intrusion (w/contact metamorphism and w/o).

Cross Section 1

Cross Section 2

Cross Section 3Word Bank: Limestone, Tilt, Sandstone, Granite, Shale, Conglomerate, Conglomerate, Unconformity, Unconformity, Sandstone

Procedure BUsing the following geologic sequence, create a geologic picture (outcrop) from the sequence given below. Draw the geologic picture using this sequence. Be sure to look at the entire sequence before trying to draw the layers.

Discussion Questions:

1. In a cross section suppose you find older rock layers on top of younger layers. Explain a probably cause for this exception to the Principle of Superposition. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Explain how contact metamorphism on an igneous intrusion can help determine the relative age of the rocks around it. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. Describe the series of events that would create an unconformity. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Correlating Rock LayersHow do scientists correlate rock layers?• Correlating means to ___________________ rock layers from area to another• Correlating is done by establishing the rocks of ___________________ and ______________in

different areas• We use ______________ ________________

Look at the diagram to the right

Which layers can be correlated?______________________o How did you know? __________________________

______________________________________________________________________________________

Which layer was eroded? ________________________________o How do you know? _______________________________

_______________________________________________

What is the correct sequence from oldest to youngest? _________________________________________________________________

Examine the outcrop to the right and determine which layers are the oldest and which are the youngest

Correlating Rock Layers Practice Questions

1.) Base your answer to the following question on the block diagrams of four rock outcrops, A, B, C and D, located within 15 kilometers of each other. The rock layers have not been overturned.

When rock layers at outcrops A, B, C and D are correlated, which rocklayer would be determined to be theoldest?

a. Marbleb. Gneissc. Quartzited. Sandstone

2.) The cross sections below show the surface bedrock in two different locations 20 miles apart. Rock layers are labeled 1, 2, 3, 4 and X. The rock layers have not been overturned.Rock layer X at location B is most likely the same relative age as which rock layer at location A?a. 2b. 3c. 1d. 4

3.) Four rock outcrops, labeled 1, 2, 3, and 4, found within the same plateau, are represented below. Index fossils found in some of the rock layers are shown. The rock layers have not been overturned.

Which layer is the youngest?

a. Sandstone in outcrop 1 b. Breccias in outcrop 2c. Sandstone in outcrop 4d. Conglomerate in outcrop 3

= sandstone = conglomerate = breccia

III. Absolute Dating Absolute Age -_________________________________ that have passed since the rock was formed

_______________________ - Atoms of the same element (so they have the same number of protons) can have different numbers of ______________; the different possible versions of each element are called _____________________________

Example: Carbon -12 Carbon -14

___________________________________- the procedure of calculating the absolute age of a rock or mineral using radioactive isotopes

Radioactive Decay- the process in which the nuclei of radioactive elements _______________ __________________, releasing fast moving particles and energy

• During radioactive decay, the _____________ of one element (parent) break down (change) to form atoms of another ________________ (daughter)

• Radioactive elements occur naturally in _____________________ rock

• Continues at a ________________ ____________, not affected by outside factors

Parent Element - the ____________, unstable, radioactive element, __________ throughout process

Daughter Element - the resulting, ____________, non radioactive product due to radioactive decay, ____________________ throughout process

Half Life- the time it takes for _______________ of the radioactive atom to decay to the daughter element

o The half life for the radioactive element _______________ changes no matter how much the starting mass of the substance is or ________________________

Determining the Absolute Age of Rocks1.) Scientists determine the amount of ____________________ material in rock

2.) Compare the ________________ amount to the _________________ amount

3.) Use the _________________ and the __________________ to determine how old the sample is

Potassium-40 is useful in dating _____________ rocks because of its ____________________ Carbon-14 is used to date _________________ because all living things contain _________________.

o _______________________ be used to date fossils older than 57, 000 years or more than 10 half lives, because the amount of ________________ left is _______________ to measure

Parent/Daughter Element Pairs Half life chart

Let’s see how this works, complete the table and shade the circle showing how the amount changed with each half life passed

Half life's past

% Parent Element % Daughter Element

Lets try some practice problems.

1.) You have a fossil that contains Carbon-14, you know that the total mass of that sample was 40mg. You have determined that there is 30 mg of Nitrogen-14 in the fossil.

Answer the following:a.) How many half life’s have passed?b.) This fossil was formed how many years ago?c.) What percentage of parent element is present?d.) What percentage of daughter element is present?

# of Half Life’s past

Time % Parent Element

Mass Parent Element

% daughter Element

Mass Daughter Element

2.) You have a sample of rock with an unknown radioactive material in it, but you have information stating that it was formed 3.9 billion years ago. You know that the parent element is 7.5mg and the daughter element is 52.5mg.

Answer the following:a.) What % is the parent elementb.) What % is the daughter elementc.) How many half life’s have passedd.) What is the parent element, what is the daughter element?

# of Half Life’s past

Time % Parent Element

Mass Parent Element

% daughter Element

Mass Daughter Element

Practice Absolute DatingThe data table shows the mass of a sample of radioactive carbon-14 remaining after each half life.

1.) On the grid, construct a graph by plotting the data for the mass of carbon-14 in the sample for each half-life shown on the data table.

2.) Identify the stable disintegration product of the radioactive isotope carbon-14

____________________________________3.) Determine the number of grams of

carbon-14 remaining in this sample at 17,100 years. _______________________

Use the graph to answer questions 4 and 5

4.) Based on the graph, the half-life of this radioactive isotope is

a. 3 hb. 9hc. 12 hd. 6 h

5.) Based on the graph, what is the approximate number of radioactive atoms in Isotope X that are present when 8 hours of decay has occurred?

a. 90b. 155c. 200d. 115

6.) The age of which index fossil could be determined by using carbon-14?

Early Earth

How did Earth Form?Using radioactive dating, scientists have determined that the oldest rocks ever found on Earth are about 4 billion years old. But scientists think Earth formed even earlier than that.

The Age of EarthAccording to these scientists’ hypothesis, Earth collided with another object. This means Earth and the moon are about the same age. Scientists have used radioactive dating to find the age of moon rocks that astronauts brought back to Earth. The oldest moon rocks are about 4.6 billion years old. Scientists infer that Earth is also roughly 4.6 billion years old-only a little older than these moon rocks.

Earth Takes ShapeScientists think that Earth began as a ball of dust, rock and ice in space. Gravity pulled this mass together. As Earth grew larger, its gravity increased, pulling in more dist, rock and ice nearby. The energy from collisions with these materials raised Earth’s temperature until the planet was very hot. Scientists think that Earth may have become so hot that it melted. Denser materials sand toward the center, forming Earth’s dense, iron core. Less dense, molten material hardened over time to form Earth’s outer layers-the solid crust and mantle.

The AtmosphereEarly Earth may have included light gases such as hydrogen and helium. Then the sun released strong bursts of particles called the solar wind. Earth’s gravity could not hold the light gases, and the solar wind blew away Earth’s first atmosphere.After Earth lost its first atmosphere, a second atmosphere formed. Volcanic eruptions and collisions with comets added carbon dioxide, water vapor, nitrogen and other gases to the atmosphere. A comet is a ball of dust, gas and ice that orbits the sun.

The OceansAt first, Earth’s surface was too hot for water to remain a liquid. All water remained as water vapor. As Earth’s surface cooled, the water vapor began to condense to form rain. The rainwater gradually accumulated and formed oceans. The oceans absorbed much of the carbon dioxide from the atmosphere.

The ContinentsDuring early Precambrian Time, much of Earth’s rock cooled and hardened. Less than 500 million years after Earth formed, the rock at the surface formed continents. Scientists have found that the continents move very slowly over Earth’s surface because of forces inside Earth. Over billions of years, Earth’s landmasses have repeatedly formed, broken apart, and then crashed together again.

Early OrganismsScientists cannot pinpoint when or where life began on Earth. But scientists have found fossils of single-celled organisms in rocks that formed about 3.5 billion years ago. Scientists think that all other forms of life on Earth arose from these simple organisms. Bacteria are probably similar to these early organisms. About 2.5 billion years ago, many organisms began using energy from the sun to make food. This process is called photosynthesis. One waste product of photosynthesis is oxygen. As organisms released oxygen, the amount of oxygen in the atmosphere slowly grew. Some oxygen changed into a solid form called ozone. The atmosphere developed an ozone layer that blocked the ultraviolet rays of the sun. Shielded from these rays, organisms could live on land.