Calcite in Mats
Written November 5, 2009
[We have web access! I'll update my classification if it continues.]
Three days ago, Dale collected some samples from 19.5 meters (64 feet) in the calcified zone and 10 meters (34 feet) off boulders. The mats all had the mineral calcite in them. Calcite forms when the activities (sort-of like concentrations) of calcium (Ca2+) and bicarbonate (HCO3-) in the water are high. Bacteria change the concentration of bicarbonate in the water when they photosynthesize or respire and organic molecules can absorb or release calcium. Thus, bacterial communities can influence calcite precipitation (see YouTube videos). This calcite is what can turn the microbial communities into fossils.
I spent parts of the last two days cleaning the mat, rock flour, and sand off the calcite. I use tweezers to pull off some of the mat and a pipette to squirt water on the sample to remove other bits of mat, rock flour, and sand. Sometimes I hold the sample with tweezers and shake it in a bit of water. When there is lots of mat, it feels like I’m dissecting an animal. When there is lots of sediment, I feel like an archeologist. In both cases, I go from a gooey mass to interesting bits of hard calcite.
The calcite varies substantially from place to place, reflecting differences in the fossilization process. In some places, there are only a few crystals, barely connected - the fossilization process is just starting. In others, the calcite is in robust rods or sheets forming very rigid structures. These are much closer to fossils that could persist in the rock record. In many cases, there are patches of mat that are highly calcified right next to patches that have no calcite in them at all. Why? What is the difference in the biology and chemistry of these areas? I don’t know yet. Right now, I’m in the process of developing some hypotheses on the differences. I need a model of how calcification varies to direct my observations.
This is one of my favorite parts of science. I have made some observations (the amount and style of calcite varies) and have a question (why?). Now I have to figure out what to observe next to start to answer my question, to refine my question into one that is specific enough to answer. One way to start is to categorize my bits of calcite. To separate things into different groups, you look for similarities and differences. This requires deciding what is important about the bits. For example, some are slightly darker grey than others, possibly because they have more glacial flour mixed with the calcite. Is that feature more important than the shape? Or do I categorize them by both color and shape?
Even in writing these questions down, I’m starting to understand the samples better. The darker grey samples come in only two basic shapes: thin smooth layers and thick knobby discontinuous layers. If I make these two categories, how do they relate to each other in terms of the process of calcification?
This is my scientific process right now. I love it.
[We have web access! I'll update my classification if it continues.]
Three days ago, Dale collected some samples from 19.5 meters (64 feet) in the calcified zone and 10 meters (34 feet) off boulders. The mats all had the mineral calcite in them. Calcite forms when the activities (sort-of like concentrations) of calcium (Ca2+) and bicarbonate (HCO3-) in the water are high. Bacteria change the concentration of bicarbonate in the water when they photosynthesize or respire and organic molecules can absorb or release calcium. Thus, bacterial communities can influence calcite precipitation (see YouTube videos). This calcite is what can turn the microbial communities into fossils.
I spent parts of the last two days cleaning the mat, rock flour, and sand off the calcite. I use tweezers to pull off some of the mat and a pipette to squirt water on the sample to remove other bits of mat, rock flour, and sand. Sometimes I hold the sample with tweezers and shake it in a bit of water. When there is lots of mat, it feels like I’m dissecting an animal. When there is lots of sediment, I feel like an archeologist. In both cases, I go from a gooey mass to interesting bits of hard calcite.
The calcite varies substantially from place to place, reflecting differences in the fossilization process. In some places, there are only a few crystals, barely connected - the fossilization process is just starting. In others, the calcite is in robust rods or sheets forming very rigid structures. These are much closer to fossils that could persist in the rock record. In many cases, there are patches of mat that are highly calcified right next to patches that have no calcite in them at all. Why? What is the difference in the biology and chemistry of these areas? I don’t know yet. Right now, I’m in the process of developing some hypotheses on the differences. I need a model of how calcification varies to direct my observations.
This is one of my favorite parts of science. I have made some observations (the amount and style of calcite varies) and have a question (why?). Now I have to figure out what to observe next to start to answer my question, to refine my question into one that is specific enough to answer. One way to start is to categorize my bits of calcite. To separate things into different groups, you look for similarities and differences. This requires deciding what is important about the bits. For example, some are slightly darker grey than others, possibly because they have more glacial flour mixed with the calcite. Is that feature more important than the shape? Or do I categorize them by both color and shape?
Even in writing these questions down, I’m starting to understand the samples better. The darker grey samples come in only two basic shapes: thin smooth layers and thick knobby discontinuous layers. If I make these two categories, how do they relate to each other in terms of the process of calcification?
This is my scientific process right now. I love it.
