Lecture 26
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Metamorphic rocks form under?
extremely high temperatures and pressure conditions, like at a continental-continental plate boundary
What are the 3 grades of metamorphic rocks?
slate low-grade, schist medium-grade, and gneiss high-grade
What are the 3 types of metamorphic rocks in NYC?
Fordham gneiss found 1.1 billion years ago, Inwood marble from 450 million years ago, and manhattan schist from 450 million years ago
What are the grades of Manhattan Schist and Fordham Gneiss?
medium, and high grade, as Gneiss is formed at a deeper level and higher temperature
When was much of New England added?
during the taconic and acadian orogenies
What is sedimentary rock?
Rocks that are products of physical and chemical weathering and are generally classified based on the size of the grains (shale, sandstone, conglomerate)
What is weathering?
a process that yields particles and dissolves ions that become raw materials for sedimentary rocks
What are the first 2 steps in making sedimentary rocks?
Weathing where rocks are exposed to the weather and worn down, and transported from the site of weathering to the site of deposition
What are the erosional forces?
water (most common), glaciers (most powerful), and wind
What are the last two steps in making sedimentary rocks?
depositions aka sedimentation, and lithification
What is the rock cycle?
Rocks are created and destoryed in cycles. The rock cycle describes the formation, breakdown, and reformation of a rock as a result of sedimentary, igneous, and metamorphic processes.
What is the geological time scale?
A calendar of Earth history that subdivides geological history into units, which was originally created using relative dates based on fossils
What are the 4 main eons?
The Hadean 4540 millions of years ago, the archean which started 4000 years ago, the proterozioc which was 2500 millions of years ago, and the phanerozic which is where there are lots of fossils
What is an era?
subdivision of an eon, that are then subdivided into periods
What are the eras of the phanerozioc eon?
cenozoic (recent life), mesozoic (middle life), and paleozoic (ancient life
When did the first oceanic crust form?
4.5 billion years ago
What was early earth’s atmosphere vs todays?
Early earth - water vapor, carbon dioxide, nitrogen. Today - nitrogen 78, oxygen 21, CO2 +Argon+others
Why were there no photosynthesizing microbes before 2.7-1.8 billion years ago?
there was little to no free oxygen in the atmosphere <1% of present levels, and at 2.7 Ga it reached 1-5% of today’s levels
How do we know Earth’s early atmosphere was oxygen poor?
Occurrences of minerals that only form in non-oxidizing environments in Archean sediments. Archean rocks are often dark because they contain free C
What evidence is there for free oxygen in the atmosphere?
banded iron formation(BIFs) - 2.6 to 1.8 Ga.
What are BIFs
Sedimentary rock formed by precipitation formed in oceans, that consists of repeated, think layers of black iron oxides, alternating with bands of iron poor shales and cherts, often red in color. Fe is soluble in the absence of O, but insoluble in the presence of O
What was the Grenville Orogeny at 1 billion years ago?
An episode of mountain building where part of the continental collisions involved the formation of Rodinia, the Fordham Gneiss -bed rock, and Rodinia breaking apart 750 million years ago