Astronomy 2021A/B Lecture Notes - Fossil, Geochemistry, Half-Life

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Published on 22 Apr 2013
School
Western University
Department
Astronomy
Course
Astronomy 2021A/B
Professor
Astronomy Lecture #4
Search for Life in the Universe
Midterm 25% - starts at 7 PM
40 Multiple Choice
8:15 Lecture #5 begins
TA Monday 1-2, Tuesday 2-3 PAB 49
Or PB 312
Prof Wed 12:30-2:30
The Earth From Space
Earth: The La-Z Boy of the Terrestrial Worlds
Earth’s moon is dry and airless
Mars next best chance for life
Geology
A study of earth” but we mean study of processes and features that shape
our world
o Three meanings to focus on:
Volcanism
Plate tectonics
Magnetic field
Earth has a long history
We can study rocks and fossils
Contain info about when they were formed
The geological record
Arrival, birth and evolution of life on earth
Understand when they formed and what Earth was like when they formed
Types of rocks: Igneous, Metamorphic, and Sedimentary
Igneous
o Solidified rock
o Pure coming from heart of the world
Metamorphic
o Rock that has gone through transformations
Sedimentary
o Useful for revealing history
o Layers
All go through a cycle
Any type of rock is made from different minerals (crystals of certain
elements) like silicates or carbonates
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A silicate would be like quartz, carbonate is like graphite or diamond
Any of these types of rocks could be diff versions of these
o Rock types tell us how it was made, teaches us the history of Earth
Sedimentary Strata
Diff layers of sediment
River deposit some material (minerals) and deposits them in lake head
Over time keeps laying new layers
End up with diff layers
If river carves through the sedimentary layer, you can see it and reveal the
layers
We can find things in the layers like fossils
We can figure out the layers age
So when things appeared
o Few diff layers, two diff hills
o Will have two layers the same = the same age
o Same process, same age
o At the top, most recent
o At the bottom, first layer that was made (ancient stuff)
o This is crucial because we want to determine the age
A rock found above a layer that’s 100 million yrs old and below a layer that’s
10 million years old, must be between 10 and 100 million years old
And we never found fossil that didn’t match (like a dinosaur bone found in a
10 million year old layer)
How to analyze rock
Beyond just type:
o Mineralogical analysis formation temp, pressure
o Chemical analysis what’s it made of
o Isotropic analysis age
Radiometric dating
o Radioactive decay transforms elements into other elements on a well-
known timescale
o Example: potassium-40 decays into Argon-40
A proton turns into a neutron
Potassium has one more proton it changes to neutron
One atom can never measure age of this atom
But can measure age of rock
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Document Summary

Midterm 25% - starts at 7 pm. Ta monday 1-2, tuesday 2-3 pab 49. Earth: the la-z boy of the terrestrial worlds. Mars next best chance for life. A study of earth but we mean study of processes and features that shape our world: three meanings to focus on: Contain info about when they were formed. Arrival, birth and evolution of life on earth. Understand when they formed and what earth was like when they formed. Igneous: solidified rock, pure coming from heart of the world. Metamorphic: rock that has gone through transformations. Sedimentary: useful for revealing history, layers. Any type of rock is made from different minerals (crystals of certain elements) like silicates or carbonates. A silicate would be like quartz, carbonate is like graphite or diamond. Any of these types of rocks could be diff versions of these: rock types tell us how it was made, teaches us the history of earth.

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