Why I'm Going...
As a professor, my job is to learn things that no one else has known before and to share that knowledge with others, especially students. It's the best job in the world. As a geologist, I try to learn new things about the earth and its history by making observations of the natural world, doing experiments, analyzing samples, and developing computer models.
One of the unknown questions I am most interested in right now is how photosynthesis evolved. We know that bacteria were the first to do it, and the bacteria that release oxygen (O2) are called cyanobacteria. (Plants and algae adopted cyanobacteria, incorporating the cyanobacteria into their own cells. The chloroplasts in plants and algae started off a billion years ago as free-living bacteria, and they evolved with plants and algae to become the chloroplasts. We know this from similarities in the genes in chloroplasts and cyanobacteria.) Based on the chemistry of rocks, we also know that oxygen first accumulated in the atmosphere about 2.4 billion years ago. Since photosynthesis is the only major source of oxygen for the atmosphere, we can reasonably conclude that cyanobacteria were around on earth, releasing oxygen prior to 2.4 billion years ago. What about before then? Could there have been cyanobacteria but just not enough for them to change the chemistry of the rocks? We don't know the answer to these questions, and I'm trying to find out.
So what does this have to do with a lake in Antarctica? I'm getting there...
There are certain types of fossilized communities of bacteria preserved in rocks that are 2.5 to 3.0 billion years old. I want to know if these fossils were originally cyanobacteria. One way I'm trying to figure this out is to see what sorts of fossils modern communities of bacteria might make. Are they similar? How are they different? Can you tell the difference between fossil cyanobacterial communities and communities of other types of bacteria? Unfortunately, today, there are lots of worms, bugs, and fish that like to eat cyanobacterial communities. This changes the way they would look if they became fossils. But if you go to a place where there are very very few worms, bugs, and fish, maybe the communities of bacteria will look more like they did 2.5 billion years ago.
Lake Joyce in Antarctica has 6 meters of ice covering it all year round. It's too cold for bugs and fish to live so there aren't any to eat the bacteria, but there might be some tiny worms. (We'll find out!) Thus, it's a good place to go look for communities of bacteria that might be similar to those that lived 2.5 billion years ago. Also, the communities of bacteria have the mineral calcite forming on them in some parts of the lake. This is the first step to becoming a fossil, so we can also study how a living community changes as it becomes a fossil.
Here are some of the questions our group hopes to answer that no one has answered before: 1) What types of cyanobacteria live in Lake Joyce? 2) What do their communities look like? Dale has some photos of them from 10 years ago, but we'll have much more time to describe their morphology this time.
3) How do they change the chemistry of the water? They produce oxygen and use up carbon dioxide. By removing carbon dioxide, they make the pH of the water higher. 4) Do these chemical changes affect how they are fossilized? If pH gets higher, the mineral calcite is more likely to form. Are they changing pH enough that they are fossilizing themselves by making minerals form? An alternative hypothesis is that the chemistry changes because ground water seaps into the lake where the calcite forms.
There are many other questions as well. We will also learn unexpected things. Discovering things no one has known before is really exciting. It adds to my Antarctic adventure!
One of the unknown questions I am most interested in right now is how photosynthesis evolved. We know that bacteria were the first to do it, and the bacteria that release oxygen (O2) are called cyanobacteria. (Plants and algae adopted cyanobacteria, incorporating the cyanobacteria into their own cells. The chloroplasts in plants and algae started off a billion years ago as free-living bacteria, and they evolved with plants and algae to become the chloroplasts. We know this from similarities in the genes in chloroplasts and cyanobacteria.) Based on the chemistry of rocks, we also know that oxygen first accumulated in the atmosphere about 2.4 billion years ago. Since photosynthesis is the only major source of oxygen for the atmosphere, we can reasonably conclude that cyanobacteria were around on earth, releasing oxygen prior to 2.4 billion years ago. What about before then? Could there have been cyanobacteria but just not enough for them to change the chemistry of the rocks? We don't know the answer to these questions, and I'm trying to find out.
So what does this have to do with a lake in Antarctica? I'm getting there...
There are certain types of fossilized communities of bacteria preserved in rocks that are 2.5 to 3.0 billion years old. I want to know if these fossils were originally cyanobacteria. One way I'm trying to figure this out is to see what sorts of fossils modern communities of bacteria might make. Are they similar? How are they different? Can you tell the difference between fossil cyanobacterial communities and communities of other types of bacteria? Unfortunately, today, there are lots of worms, bugs, and fish that like to eat cyanobacterial communities. This changes the way they would look if they became fossils. But if you go to a place where there are very very few worms, bugs, and fish, maybe the communities of bacteria will look more like they did 2.5 billion years ago.
Lake Joyce in Antarctica has 6 meters of ice covering it all year round. It's too cold for bugs and fish to live so there aren't any to eat the bacteria, but there might be some tiny worms. (We'll find out!) Thus, it's a good place to go look for communities of bacteria that might be similar to those that lived 2.5 billion years ago. Also, the communities of bacteria have the mineral calcite forming on them in some parts of the lake. This is the first step to becoming a fossil, so we can also study how a living community changes as it becomes a fossil.
Here are some of the questions our group hopes to answer that no one has answered before: 1) What types of cyanobacteria live in Lake Joyce? 2) What do their communities look like? Dale has some photos of them from 10 years ago, but we'll have much more time to describe their morphology this time.
Here is a picture that Dale took ~10 years ago of some of the communities in Lake Joyce with a diver wearing a dry suit in the background.
3) How do they change the chemistry of the water? They produce oxygen and use up carbon dioxide. By removing carbon dioxide, they make the pH of the water higher. 4) Do these chemical changes affect how they are fossilized? If pH gets higher, the mineral calcite is more likely to form. Are they changing pH enough that they are fossilizing themselves by making minerals form? An alternative hypothesis is that the chemistry changes because ground water seaps into the lake where the calcite forms.
There are many other questions as well. We will also learn unexpected things. Discovering things no one has known before is really exciting. It adds to my Antarctic adventure!
