Midterm Review1. The "Big Bang" is our current best model for the origin and evolution of the Universe. Sequentially, starting with the moment of the "Big Bang" very briefly (in bulletpoints if you choose) describe the evolution of the Universe. Address the formation of matter, expansion, cooling and the first cycle of stellar formation- 13.798 billion years ago, there was the Big Bang, where all mass and energy appear to expand from a single point (and has been expanding ever since)- During the first instant, only energy—no matter—was present- Then: within a few seconds, Hydrogen was first formedthey begin to stick together and form HeliumLight nuclei (atomic no. < 5) by Big Bang nucleosynthesis (beryllium, lithium) The Universe expanded and cooledAfter abut 380 000 years of expansion and cooling, atoms began to bond; electrons attached to the nuclei. Hydrogen formed H2molecules—the fuel of starsAtoms and molecules coalesced into gaseous nebulaeBy 100 million years, gravity began to pull together gaseous nebulaeMass in nebulae was not uniformly distributed. Region where mass was concentrated began to pull in gas.The region gained mass and density.Mass compacted into a smaller region and began to rotate.Rotation rate increased, developing a disk shape.The central ball of the disk became hot enough to glow.A protostar was born!
2. Major spreading ridges – especially the mid-Atlantic ridge and the East Pacific rise and spreading ratesmid atlantic ridge spreads slowly,east pacific rise spreads quickly: because it spreads quickly, the ocean depth don’t fall off as quickly from the ridge compared to the mid-atlanticSea-floor spreading progression.Early stageRifting of a continent progresses to mid-ocean ridgeformation.Forms a long, thin ocean basin with young oceanic crust.With time, continuing widening of the oceanMaterial is upwelling at the MOR, it is spreading apart when itfreezes on the surface into the oceanic crust and into the lithosphereThe closer to the ridge, the younger the ocean floorSea-floor spreading opens the axial rift valley. Rising asthenosphere melts, forming mafic magma. Pooled magma solidifies into oceanic crustal rockSpreading rates range from approximately 10–200 mm/yr.Slow-spreading ridges such as the Mid-Atlantic Ridge have spread much less far (showing a narrower profile) than faster ridges such as the East Pacific Rise (wider profile) for the same amount of time Slow-spreading ridges (less than 40 mm/yr) generally have large rift valleys, By contrast, fast-spreading ridges (greater than 90 mm/yr) such as the East Pacific Rise lack rift valleys
3. Cascadia subduction zone off the west coast of Canada: history of events, spreading rate from ridge, collision rateConvergent plate boundary/subduction zones:Lithospheric plates move toward one another.
- Fall '09