Sunday, September 16, 2012

What Do We Want??

by Stacy Carolin
Time to get started! Just a reminder, this is our goal:

BIG GOAL: Prove that we've got a stalagmite that formed over 125,000 years ago!

Why? That was the last time that the earth was in an "inter-glacial" state similar to today's (aka no glaciers covering large parts of North America, Europe, and Asia). Right now we are in a geologic epoch called the "Holocene," and have been for the past 12,000 years. Remarkably, the climate has been incredibly stable during the Holocene, which coincidentally encompasses the Agriculture Revolution and thus rapid increase of human populations across the globe. Oppositely, climate during the earth's most recent (and much more common over the past few millions of years) GLACIAL period (pre-12,000 years ago), includes MANY abrupt climate changes (in some cases regions in northern high latitudes shifted temperature several degrees celsius over just a few decades!)

Because the last time the earth was in an "inter-glacial" period similar to what we are in today was over ONE HUNDRED THOUSAND years ago, not many records have been produced to explain what THAT period's climate was like in different regions across the globe, and many mysteries still remain. Luckily, stalagmites are a perfect tool for the job, especially for the tropics.

When a stalagmite forms from dripwater, the chemistry of the rock stores information about the chemistry of the rainwater from which it formed, which has been proven to be related to the average amount of regional tropical rainfall. So, a stalagmite that formed during this last climate period we're interested in (between about 130,000 and 115,000 years ago) is essentially a time capsule for variability in rainfall amount over the maritime continent during that period (since ours were collected in Borneo).

A stalagmite grows in layers that pile on top of each other as the water drips on it-- the stalagmites I work with usually take about 100 years to form 1mm, so a foot-long stalagmite would have taken about 30,000 years to form. The best way to understand when exactly the stalagmite did form is to determine the age of the bottom (oldest section) and top (youngest section) of it.

We will be using what's called the "U-series" dating technique to determine the age of our samples-- which I will discuss a lot more later on. All we need to know for now is that in order to do this, we need to calculate ratios of Uranium (U) atoms and Thorium (Th) atoms out of our samples. So, the VERY FIRST STEP is to actually produce samples (again, one at the top and one at the bottom) OUT of our collected stalagmites that we found fallen on the cave floor.

Let's go! Time to get out the giant rotary saw! Yessss.... :)