Earth's first atmosphere 4.6 billion years ago was most likely comprised of hydrogen and helium (two most abundant gases found in the universe!) Through the process of outgassing, the outpouring of gases from the earth's interior, many other gases were injected into the atmosphere. These include: water vapor (produced rain - rivers, lakes, oceans) carbon dioxidenitrogenAs outgassing occurred over a period of millions of years, the atmosphere evolved to its current state
Life and Evolution Diverse Ordovician Sea-Life Video Clip
Any __________ or ______, must be younger than all rocks through which it cuts. Simply put, the body of rock that is cross-cut had to be there first in order to be cut by an intruding igneous body or fault.
The following diagram represents a cross-sectional view of a portion of Earth’s crust. What is the relative age of the igneous rock? The igneous rock is older than the … The igneous rock is younger than the …
Which fossil would make the best index fossil? Found in only 1 layer (short lived) Found in all samples (widespread)
Another way of correlating layers by time is through ___________________ Volcanic ash falls
These ash falls are very ________ events. A single layer of ______ can be found over a large area, this allows geologists to make a__________________ from one location to another at the position of a common ash fall. brief ash time correlation
Igneous and metamorphic rocks work excellent for radioactive dating because at the time of crystallization (or recrystallization), a specific ratio of stable and radioactive isotopes are incorporated into the crystals.
On the other hand, sedimentary (clastic) rocks do not work well because they are composed of older, pre-existing rock fragments.
Imagine a rock forms with zircon mineral grains containing U 238 and no Pb 206 .
Basic Facts on this Isotope
Half Life of Uranium-238 (U 238 ) = 4.5 * 10 9 yr
U 238 decays to become Lead-206 (Pb 206 )
How does this Technique Work?
Decay of U-238 If this rock were to be found today, and contained a 1:1 ratio, equal quantities of both U 238 to Pb 206 , it would be concluded that the rock formed 4.5 b.y. How old would the sample be if it had a 1:3 ratio of U-238 to Pb-206?
The following diagram represents a cross-sectional view of a portion of Earth’s crust showing sedimentary rock layers that have not been overturned. The letters identify the specific layers. Which rock layer is the oldest? Youngest? DO NOW
DO NOW Please take out your Absolute Dating Lab
Do Now Clear your desks and get ready for the Quest!!!
Decay and Growth Curve of Isotopes Take out your HW! Notes Packet, p. 13 - Radon decays into radioactive solids - Half -Life of 4.5 days - Generated during the decay of Uranium - Inhalation of Radon or decay products may cause lung cancer Radon Facts
Explain how radioactive isotopes are used to find the absolute age of a rock, bone, fossil?
Practice Geologic Profiles Look at the geologic profiles, write down what you think is the correct sequence of events. Then click the mouse to advance the presentation. Repeat this process for each of the profiles.
What are the characteristics of a good index fossil? (You must know 2)
Explain why volcanic ash deposits make good index layers for rock correlation?
Fossils of organisms that lived for a short period of time over a wide geographic area Volcanic ash deposits cover a large geographic area in a relatively short period of time You and your neighbor need to be able to complete these questions. Use your notes to help (p. 14-15)
What is longer unit of time, a geologic era or a period?
What geologic period of time are we in today? Epoch?
_ __ Take out your ESRT (p. 8-9) and complete the following questions with your neighbor... An Era is larger and they are broken up into Periods Quaternary Period, Holocene Epoch
Which geologic period ended with the extinction of many kinds of marine animals, including trilobites? Which orogeny was caused by the collision of North America and Africa along a transform margin creating Pangaea? The Permian Period The Appalachian (Alleghanian) Orogeny _ __ Use your ESRT to complete the following Questions
The Devonian aged siltstone shown in the photograph below occurs as surface bedrock in Hamilton, NY. What does the presence of the fossil suggest about the environment of Hamilton during the Devonian? _ __
_ __ Use your ESRT [p. 8-9] to complete the following question
_ __ Mr. Gill's Baby Picture Please take out your ESRT
The table below gives information about the radioactive decay of carbon-14. Part of the table has been deliberately left blank for student use. After how many years will 1/128 of the original carbon-14 remain?
What is the correct order of development from the original (oldest) stage to the most recent (youngest) stage? DO NOW Work with a partner
Constructed Response Questions State one method used to correlate rock layers… State one piece of evidence why the limestone is the most resistant rock layer in the outcrops. Comparing rock texture / composition, looking for index fossils, examining sequencing of strata The limestone unit extends the furthest out of the outcrop (cliff)
Constructed Response Questions What does the discovery of Ordovician aged fossil corals in the surface bedrock of NYS cause you to infer? Parts of NYS were once in a shallow, warm marine envrionment