BIOL 215 Lecture Notes - Lecture 2: Pyrimidine, Selective Breeding, Murchison Meteorite

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BIOL215 Lecture 2 Notes
See timescale of "Chronological History of Earth"
Origin of Earth, approximately 4.6 b.y.a
Between 4.2 - 3.8 b.y.a, RNA world, the time period where RNA molecules had ability to store
information, and catalyze their own replication (evolved)
3.5 b.y.a (based on fossil remains) was first living organisms
The Big Bang Theory occurred between 10 - 15 b.y.a. and in 10-40 seconds, the world appeared. The
textbook states BBT occurred precisely 13.73 bya
Within 100 seconds of the Big Bang, quarks formed protons and neutrons = Hydrogen and Helium
The massive amount of hydrogen and helium which under gravity, caused expansion, condensation,
formation of protostars
Protostars burn producing heavier elements (up to Iron) as it loses fuel
Protostars explodes as supernova - forms our solar system (4.6 bya) where our sun was created
See diagrams (Figure 03) in textbook in regards to formation of Big Bang Theory and the solar system
The Earth was initially molten, and only after cooling much later is what we see today. The Earth is
believed to consist of a solid iron core, surrounded by an iron-sulfur liquid layer, followed by a mantle
before our oceanic crust. See Figure 04 in textbook
The continental crust is composed of various rocks in plates floating on top of the mantle. Rocks are
constantly created and destroyed as tectonic plates constantly bump into each other. This is
especially true in places where there is high volcanic activities
Earth was initially molten and composed largely of 4 elements: iron, magnesium, silicon, and oxygen.
This formed the major mass. Other elements made up smaller quantities, but were essential for life
especially when many of them are used as catalyst
We know that the Earth formed 4.6 bya because we are able to date some minerals that were created
during the initial stages of Earth's formation. Zircons (ZrSi mineral), when formed, incorporates some
impurities in their structures and sometimes include some U238 (unstable, decays to Pb206). Using
half-time, we can estimate Earth dates back to 4.6 bya
The Earth's crust formed 4.2-4.1 bya as Earth cools down. No traces of life could have occurred before
Earth's crust cooled because liquid rock kept forming and being destroyed, thus no life occurred
See Figure 05: Rock Cycle in the textbook
Liquid magma, when cooled, will crystalized into igneous rocks (which is what they used to uranium
trace)
It wasn't until igneous and metamorphic rocks eroded, which caused sediments and through
lithification, become sedimentary rocks
Since sedimentary rocks contain layers of different rocks and also contains fossils, we can use them to
find out the history of the Earth
We know that 250 mya that a supercontinent, Pangaea, existed. Various landmass pulled apart as a
result of tectonic plate shifting continuously
Meteors and comets bombard Earth 4.5 - 3.8 bya (supply lighter elements and frozen gases) - heavy
bombardment period
Atmosphere generated by volcanic out-gassing (80%) and impact bodies (20%)
CO2 (100-1000 times greater than present atmosphere levels), N2, and H2O plus trace amounts of
H2, S gases, ammonia, methane
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Document Summary

Between 4. 2 - 3. 8 b. y. a, rna world, the time period where rna molecules had ability to store information, and catalyze their own replication (evolved) 3. 5 b. y. a (based on fossil remains) was first living organisms. The big bang theory occurred between 10 - 15 b. y. a. and in 10-40 seconds, the world appeared. The textbook states bbt occurred precisely 13. 73 bya. Within 100 seconds of the big bang, quarks formed protons and neutrons = hydrogen and helium. The massive amount of hydrogen and helium which under gravity, caused expansion, condensation, formation of protostars. Protostars burn producing heavier elements (up to iron) as it loses fuel. Protostars explodes as supernova - forms our solar system (4. 6 bya) where our sun was created. See diagrams (figure 03) in textbook in regards to formation of big bang theory and the solar system. The earth was initially molten, and only after cooling much later is what we see today.

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