Class Notes (809,749)
Canada (493,782)
Biology (Sci) (2,418)
BIOL 215 (71)
Neil Price (36)
Lecture 2

BIOL215 Lecture 2 Notes.pdf

4 Pages
Unlock Document

McGill University
Biology (Sci)
BIOL 215
Neil Price

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 -40seconds, 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%) • CO 2100-1000 times greater than present atmosphere levels), N2, and H2O plus trace amounts of H2, S gases, ammonia, methane • CO 2s important (strong greenhouse gas), it absorbs IR radiation that is reemitted from the Earth • Water molecules is important as it would have created a blanket that covered the Earth, protecting it from the solar radiation Atmosphere reducing environment • • NO free oxygen (O 2 - important since O 2ould have prevented the build-up of organic molecules See comparison circle graph of atmospheric composition between 4.6 bya and today. To explain the change of atmospheric composition, we need to understand how the biology within the Earth changed As long as the Earth remained hot all volatile compounds remained in the atmosphere Once Earth cooled to <100⁰C, water condensed and formed oceans Large impact bodies would have vaporized the entire ocean, destroying any life Earth had liquid water on surface by 3.9 bya - sedimentary rocks (water to cause erosion, sort the particles, and to allow sedimentary rock types to be deposited) Gases would quickly dissolve in water because of their high solubility: 3- + • CO 2 H2O = HCO + H • HCL + H 2 = H 3 + Cl - • SO2+ H 2 = H 2O 3 These acids then dissolved rocks on land by the process of "chemical weathering" and rivers carried these salts to the ocean making it salty and adding all elements that would be used by organisms Biomarker (Graphite in quartz crystals 3.85 bya) and fossil evidence (bacteria-like fossils 3.5 bya) proves that life existed around 3.8 bya Before we consider how could life have first evolved on Earth, we must define what life is? It is: 1. Organization (into organs, tissues, cells, etc.) 2. Energy use and metabolism 3. Homeostasis 4. Replication/reproduction 5. Response to environment/stimulus Most research on the origin of life is not on fossils, but consists of laboratory research on the kinds of chemical reactions that may have taken place on Earth 4 billion years ago • Step 1 - raw materials (organic matter) • To make the building blocks, we require simple organic compounds • Organic compounds are C-rich compounds with C-C bonded together. (i.e. amino acids, hydroxy acids,
More Less

Related notes for BIOL 215

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.