Planet Earth-Lecture 7.docx

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18 Apr 2012
Lecture 7
Rocks and minerals
Quiz mostly based on lecture
Petrology: rock, study rocks and look on mineralogy
Rocks: are the only record we have of old environments on Earth
Moon rocks: valuable rocks. A lot are missing. 3 sources: US Apollo missions, soviet union missions
(on land missions) and meterorites: crater impact on moon, enter earth’s gravitational field. 400 kg
of rock have been brought back from the moon (basalt and anorphosite-similar to what makes up
Earth’s crust). Theory that Moon originated from our planet by huge impact which detached part of
our crust and mantle.
The rock cycle: three main groups of rock: sedimentary (result of weathering and erosion of older
rocks that produce sediments, loose sediments like clay, sand and boulders. They get deposited in
sedimentary basins (Lake Ontario-sedimentary basin, Hudson Bay, Atlantic ocean). They get buried
and go through lithification (turn something into rock). Many environments that sediments are
moved and deposited.
Type of sedimentary: can tell ancient environment in which it was deposited in (like picture post
cards). Rocks can undergo change due to heat and pressure to turn into metamorphic rock (change
in appearance). Difficult group of rock to deal with and difficult to identify parent type because
process of transformation can be profound. Low grade to high grade metamorphic rock. Igneous
rock: two broad subdivisions: intrusive (never see light and cool underground, cool slowly,
component crystals and component mineral have time to grow, they are intruded into other rocks,
they are coarse grained). Second type is magma (cool quickly, fine grained, make it to earth’s surface).
Because of plate tectonics, all rocs can be uplifted, eroded, weathered and that produces sediments
and whole cycle starts again. Process does not always happen this way because sedimentary and
metamorphic rock can be uplifted.
Quartz (metamorphic rock): can undergo several cycles
Poly cyclic grains: go through more than one cycle
Acasta nice: famous rock and oldest in Canada (4 billion years old). Tells us that rock cycle was
operating 4 billion years ago. Component grains give OLDER ages. So poly cyclic grains already by 4
billion years ago
What drives whole process? Mantle convection, radioactive decays. When mantle breaks down,
produces heat and that in turn produces earth’s magnetic field (creates protective shield). (All
processes happens because of uranium decay in mantle)
Once process stops, what will the only process be? Incoming meterorites.
How long will process keep going: for another 4 billion years. Earth’s life cycle half way through
Paleo environmental reconstruction: how were rocs deposited? What latitudes? What water depth?
What organisms?
Veins run through limestone. Black patch: oil. Rock has pore spaces and that’s where oil
accumulates. Create oil reservoirs.
Petroleum geologists
A rock is a naturally formed, consolidated material composed of grains of one or more minerals
A mineral is a naturally occurring, inorganic, crystalline solid that has a specific chemical
composition. They are the building blocks of rocks (have specific shape)
Minerals (4500 different types). The most important group are silicate minerals containing silicon
and oxygen and accounts for 90% of all minerals. A few silicate minerals dominate: quartz (silica
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