Tuesday, February 8, 2011

2/8/11 Class Overview


How to tell geologic time using fossils

Macroevolution - large scale evolution (one species turns into another)
Microevolution - minor evolutionary changes

-Fossils in sedimentary rocks show that macroevolution has happened
-Earth's layers show a record of life
-Layers of sediment/fossil dating don't tell exact age... only ballpark/relative
-Layers closer to Earth's surface are youngest
-Deeper down low are older

4 Eras of Time: Precambrian, Paleozoic, Mesozoic, Cenezoic

Radiometric Dating

-Measure how much radiation a fossil releases as they break down
-The amount of radiation as well as level of decay give you exact years
-Half-Life=the amount of time it takes for half of a fossil to radioactively decay
--So if a bat fossil would normally take 100 years to decay, its half-life is 50 years
--Think of the decay period (100 years) as the fossil's life, half of it is 50
-To date very old fossils, paleontologists simply use isotopes with longer half-lives
-Isotope=an atom (like the M&M's in our lab today) with uneven numbers of protons/neutrons

Continental Drift: Pangaea

-The idea that all land in the world used to be one huge piece of land
-It broke apart slowly into the separate pieces of today
-Still breaking apart.... 2 cm/year (Thanks Nick)
-Impacts of land break=extinctions, species isolation according to continents
-Plate boundaries=place where 2 plates meet
-Earthquakes occur at plate boundaries

In-Class Lab: M&M's

Purpose: To learn how radiometric dating and radioactive decay work

-The M&M's represented atoms that were radioactively decaying
-We took 100 and kept decaying them randomly by spreading them out and removing the ones that had no "M" inscribed on top. The removal represented decay~
-Once they decayed to around 50, the half-life was found by seeing how much time it took to get to 50 because half-life is a time period

Quiz on all evolution tomorrow.

Next Scribe: Bridget

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