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Lecture 5

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Biological Sciences
Rudy Boonstra

LECTURE 5 October 9, 2007 We talked about proxies, evidence that has been mounted to support the claim that there have been major changes. The strongest evidence comes from looking at the small changes in ratios of oxygen. There are various isotopes that we looked at. Scientists looked at small changes of temperatures and the amount of ice in the Antarctic and Greenland. One key organism for about the last 65 years looks like this. They are called Foraminifera or Forams. They have little strands that form and complete a dynamic web. There are 275,000 of these species but each of them forms a test which is the shell of the Foram. You find them in the worlds oceans and other places and when they die they rain down to the floor of the ocean. You have large concentrations of these and each can be identified as species. They are used as bio-indicators. What the environment was and also temperature indicators. They incorporate into their shell calcium carbonate CaCO 3nd the critical bit is the oxygen. WE have known about these tests up to 540 million years ago. So from the start of visible life on the planet we have these guys sitting on the floors of the oceans telling us things. Scientists have isolated the ones that are indicators. In the 1960s you have research vessels that were deep sea drill units that drilled into the floor of the oceans and brought up cores. Then they would bisect the cores to try to understand the pattern and what they told us about the past. They got this information as a by-product as they were originally interested in oil. Going back to the oxygen 18 story, if you look at the ratio incorporated in things like Forams, the ratio between 18 and 16 will tell you certain signatures. The ratio that is incorporated changes depending on temperature of the water that they grow in. So a change of only about .2 partsthousand tells them there is a 1C decline in the surrounding water. This is sufficient to estimate the temperature of the water that the Forams grew in. The colder the water, if you think that the oxygen 18 have 2 more neutrons, the colder the less the vibrational advantages oxygen 18 has. Under cold conditions oxygen 16 and 18 are taken up in a similar ratio. Less 16 is incorporated in warm conditions than under cold conditions. So this is a signature of temperature. They look at oxygen 18 in the calcite in the tests. There is a bit of a hook in that this ratio is good only when there isnt a lot of ice on the planet. Where there are not huge ice sheets it is a good signature of temperature. AS the ice sheet increase oxygen 16 evaporates more than 18 so there is a concentration of oxygen 18 in the worlds oceans. Now it tells you that you are getting a more concentratedenriched ocean environment. So it tells you how much ice volume there is. How much total water on the planet is stored in ice sheets? You can get a good signature of what the planet looks like and that is what they used. BGYC58H3F.October,9, 2007 LECTURE 5 1
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