Aim: How do Scientists Read Rocks? Do Now: In your notes, answer the following question. Of the three types of rocks we have discussed (Igneous, Sedimentary and Metamorphic), which one do you think would be able to hold clues to Earth’s past? Why?
Aim: How do Scientists Read Rocks? Do Now: In your notes, answer the following question. Of the three types of rocks we have discussed (Igneous, Sedimentary.
Dec 29, 2015
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Aim: How do Scientists Read Rocks?
Do Now:
In your notes, answer the following question. Of the three types of rocks we have discussed (Igneous, Sedimentary and Metamorphic), which one do you think would be able to hold clues to Earth’s past? Why?
Outcrop – section of rock exposed at the surface that shows a geologic sequence.
I. Reading Earth’s History• Uniformitarianism - processes we
observe today are most likely the same processes that occurred millions of years ago.
When in Earth’s
history does this painting
show?
Devonian ~360 mya
Today (2014)
Triassic ~200 mya
• Relative dating - tells us the sequence in which events occurred.
*Does not tell us the actual age or use numbers to express time.
II. Rules for Relative Dating:
A.Law of Superposition - sedimentary layers are created flat and
even first.- the oldest layers are at the bottom.
B. Law of Original Horizontality - folds disturb these layers after they are lithified .
How did the sequence change in picture below? What
caused this?
C. Law of Cross-Cutting Relationships- layers can be cut afterwards by intrusions and faults.
How did the sequence change in
picture below?
- Intrusions are layers of magma that melt through pre-existing rock.
- Contact Metamorphism – occurs as intrusion touches and metamorphosis's the surrounding rock.
Can you cause the metamorphism of layer that does not exist yet?
Which comes first, the rock being metamorphosized or the magma?
NO
The rock being metamorphosized
III. Important Features
• Volcanic Eruptions –
occur at one specific time and leaves a layers of ash which marks the time eruption.
K-T ash Boundary which marks the end of the Cretaceous Period and the beginning of the Paleogene Period. This layer is 65 million years old and below this layer, scientists find fossils of dinosaurs. Above this layer, there are no dinosaur fossils.
Do not copy
•Unconformity (UNC)-
- a gap in thesedimentary rockrecord.
- caused by erosion
VIDEO 1
Closure 1: Place the letters in relative order from oldest to youngest.
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