Geologic Time Tutoring Session: Lessons 1 and 2

Lesson 1 Geologic Time

What is the “Geologic Time Scale”?

Huge sections of time are broken down into smaller groups of time: Geologic time scale: Huge sections of time are broken down into smaller groups of time:

Geologic time scale: Huge sections of time are broken down into smaller groups of time: Eons, Eras, Periods, and Epochs

Geologic time scale: Huge sections of time are broken down into smaller groups of time: Eons, Eras, Periods, and Epochs Eon is the largest time block (kind of like what we would think of as years). Era is a little less time (like months) Period would be shorter time (like weeks) Epochs are even shorter (like days) (**No different then when we take years and divide them into months, weeks, and days.)

Precambrian Period (the beginning)

(next after the 1st period) Paleozoic Eon (next after the 1st period)

(later – this is the time of the dinosaur) Mesozoic Eon (later – this is the time of the dinosaur)

Cenozoic Era (NOW!!)

What to do for Lesson 01:

Cont.: What to do for Lesson 01: Don’t forget your “reflection questions”!! GREAT job!!! Turn this into your teacher now!

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Lesson 2 Relative and Absolute Time

Objectives for this lesson:

Fossils What are they??

Fossils “Fossils are rocks that formed from the remnants (what’s left) of once-living things. All living organisms, under the right conditions, can be fossilized.”

Fossils Can you name different types of fossils?

Fossils Freezing Mold Petrification Crystallization “Fossils are rocks that formed from the remnants (what’s left) of once-living things. All living organisms, under the right conditions, can be fossilized.” Crystallization Freezing Petrification Mold

Casts Molds When something is filled with sediment (rocks) and makes it look 3-D. An imprint of something that was once living.

Petrification When something is filled with atoms of rock material; this makes them very hard (rock). *Commonly found with wood.

Freezing Crystallization When a living organism gets stuck in something sticky (like sap) the sap and the organism harden and get preserved. Freezing An organism gets frozen and the super cold temps prevent it from decaying; therefore preserving it. Crystallization

Trace Fossils: What is this (trace fossil)? Can you give me an example of this?

Trace Fossils: The remains of an organism's activities but not of the organism itself.

Trace Fossils: The remains of an organism's activities but not of the organism itself. EXAMPLES: -broken eggshells from a dinosaur's nest are trace fossils. -footprints from an organism -chewed section of a plant -”coprolites” fossilized dung or feces (meaning: poop)

What are the two types of dating which geologists can use to make the timelines?

relative dating and absolute dating. There are two types of dating which geologists can use to make the timelines: relative dating and absolute dating. Relative dating does not give an exact age (in years) to rocks or geologic events…

Instead, relative dating puts the events in sequential order; the oldest comes first, and all the rest of the events follow after, on the “relative dating timeline”. Example of relative dating (putting events in sequential order):

Geologic Assumptions: Since there weren’t scientists around during the formation of the Earth (or for any of the geologic history of Earth) they (scientists) need to rely on carefully recorded observations, so they can make assumptions about these things. These types of assumptions are called principles, and in these cases, observations made by the scientific community, over time, have repeatedly supported the assumptions. Geologic Assumptions:

Geologic Assumptions: Since there weren’t scientists around during the formation of the Earth (or for any of the geologic history of Earth) they (scientists) need to rely on carefully recorded observations, so they can make assumptions about these things. These types of assumptions are called principles, and in these cases, observations made by the scientific community, over time, have repeatedly supported the assumptions. Geologic Assumptions: 1. Uniformitarianism 2. The Principle of Superposition 3. The Principle of Original Horizontality 4. The Principle of Faunal Succession

By studying the rocks on Earth, geologists (people who study rocks) can make a chart that outlines the geologic periods of time when rocks were formed.

Uniformitarianism What is it? What can they assume with this?

Uniformitarianism What is it? The belief that all of the processes (things) that are shaping the Earth today were the same processes (things) at work in the past; (also that these processes occurred at the same rate and in the same way as they do today). What can they assume with this? Geologists can study how fast a process is occurring today, (like formation of sedimentary rock layers or erosion), and make then they can make assumptions about how the processes occurred in the past. Doing this can help them form relative time lines for past events.

The Principle of Superposition What is this one? What can they assume with this?

The Principle of Superposition What is this one? In layers of rock that have been undisturbed, (or as geologists say, "un-deformed,“) the lowest layers formed first, then the next, and the next, and so on up to the top layer. What can they assume with this? That the oldest layer is on the bottom and the layers get younger and younger as you go up.

Original Horizontality The Principle of Original Horizontality What is this one? What can they assume with this?

Original Horizontality The Principle of Original Horizontality What is this one? This tells us that when sedimentary rock layers are first formed, the sediments fall in horizontal layers. What can they assume with this? Using this principle, (plus knowing that movements of the crust can bend, fold, twist, break, and move rock layers) we can assume that if we see several layers of rocks that are in any form other than horizontal, they must have been acted upon by a disturbance of the crust of some kind.

The Principle of Faunal Succession With this principle we focus on the fossils found in rock layers. If we can estimate the age of the fossils, we can make assumptions about the age of the sedimentary rock layer in which the fossil is found.

Additional things to consider: The Law of Cross-Cutting Relationships: An igneous rock intrusion is younger than the rocks into which it has intruded. The Law of Unconformity: An unconformity is a place where some of the existing rock layers have been eroded by water or wind or changed in some way causing pieces to be missing. The Law of Deformity: A deformity may be a tilting, faulting, or folding of existing rock layers. Therefore, for the rock layers to be deformed, they must be older than the event that deformed them.

What is the order?

What is the order?

What is the order? An unconformity is a place where some of the existing rock layers have been eroded by water or wind (Hint: if wind is hitting it what layer would it be?) An igneous intrusion is younger than the rocks into which it has intruded (goes through).

More advanced dating techniques have allowed geologists to get more exact dates. SO… Absolute dating is the: The measurement of time in definite periods of time and is measured with something that gives us a definite (exact) time. It assigns specific dates to rocks and geologic events.

Radiometric dating: All rocks contain radioactive material that decays over time. The rate of radioactive decay allows scientists to establish the absolute age of a rock. ** the most common radioactive element is carbon-14 found in all living organisms. Radioactive decay starts with only parent element (an unstable isotope). Because it's unstable, it will decay into a stable daughter element. The time it takes for half of the amount of parent element to decay is constant, (and known as half-life). After one half-life, half of the material is the parent element and the other half is more stable daughter element. After another half life, one-fourth will be the parent element. As the substance keeps decaying, the amount of parent element will shrink, although it will never be completely gone. The substance would then mostly consist of the daughter element.

What to do for Lesson 02: