lecture_notes_11_28_07

lecture_notes_11_28_07 - Lecture Notes 11-28-07 History of...

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Lecture Notes 11-28-07 History of Life on Earth How Old is the Earth? Geological Observations: The Law of Superposition Radioactive Decay Radioactive isotopes decay in a regular pattern, changing to another element or to a stable isotope of the same element 14 C has a half-life of 5,700 years and decays to Nitrogen 14 40 K has a half-life of 1.3 billion years and decays to calcium 40 and argon 40 in a known proportion. By comparing the ratio of the amount of the parent isotope present to its daughter product, the age of rocks can be estimated. There are many such isotope systems in use Current Estimate: Earth is 4.5 to 4.8 billion years old
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Major Physical Changes in the Earth 1. The earth is cooling, loosing heat generated when it was formed. The radioactive furnace at its core is weakening. 2. The crust of the earth is made up of plates that are approximately 40 km thick. The plates float on a fluid mantle, propelled by the heat generated by the radioactive decay of the earth’s core. Plate Tectonics When the plates collide, mountains are formed. When plate slide past one another, earthquakes can result. The plates have moved around the earth over time, resulting in the coalescing or separation of landmasses—continental drift. As the plates move together or drift apart, the oceans become deeper or shallower, and the climates of the landmasses change, thus changing environmental selection pressures.
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With the cooling of the earth’s core, the movement of the plates of the crust of the earth is slowing. 3. The climate of the earth has fluctuated between warm-humid and cool-dry periods, in part due to changes in the earth’s orbit. The cool-dry periods are characterized by repeated glaciations. Some climate changes occurred in as few as 5,000 years. 4. The oxygen level of the earth has increased through time, and an ozone layer has developed in the atmosphere, due to the activities of photosynthetic organisms 5. Meteor strikes.
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This note was uploaded on 04/29/2008 for the course BIOCORE 301 taught by Professor Howell during the Fall '07 term at Wisconsin.

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lecture_notes_11_28_07 - Lecture Notes 11-28-07 History of...

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