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Molecular Data

We've had another look now at this event by using sequencing of modern metazoan DNA and they've done this with a number of different genes. There was a paper published last year by my friend Jeff Levington and two other scientists. They analyzed five different genes, genes like 18-S and cytochrome-C, and others. They did a very careful analysis and compared those genes where they may have appeared in the fossil record, got control on them time-wise, and came to the conclusion that metazoans diverged 1.2 billion years ago. Another paleontologist, Simon Conway Morris, examined that same set of data, and said you can't use three or so of these genes, you can only use two of them and that gave him a date of 700+ million years, still 150 or so million years before the time we see the first shelly fossils.

None of this though takes into account the other organisms that I was talking about, the algae, protozoans and so forth. It only considers the metazoans. Let's look at some of these hypotheses. We can sort them into intrinsic and extrinsic factors 64textS.jpg. These are the things that may have affected this great radiation of animals shortly after their first appearance in the Vendian. Intrinsic factors are those that are characteristic of and restricted to a particular group, like animals, because of its biology. For example, the evolution of sex, of regulatory genes, of body size, or habitat. But what I'm trying to impress upon you is that it's not animals alone that radiate--it's also algae, maybe even the bacteria, calcareous algae, radiolarians, foraminifera and other fossils too. Therefore, I can focus on what we call the extrinsic factors, those that are not really part of the biology of the organisms but that would effect all organisms in an ecosystem or in all ecosystems alike, such as sea level changes, temperature fluctuations, glaciation, and many others.

So let's take a look at some of these. Here are some 65text2S.jpg intrinsic causes of these things. None of these really can account for the radiation in all groups. These are metazoan-bound for the most part. When I talk to my metazoan colleagues, they say: "Oh well, those other fossils don't count. They're only single celled". Yeah, but they're pretty complex. So these kinds of things really have been put out as metazoan-bound hypotheses. There are more hypotheses than what I've listed here. You wouldn't be able to read the slide if I put them all up there because there are lots of them. But there are some really interesting ideas. Large-size with primitive skeletons, but we've got radiolarians and foraminifera which are tiny and have minuscule skeletons. The evolution of sex, that's always very important. But foraminifera and some of these algae have sex too. The evolution of regulatory genes, well they have them. Why should they all have happened at the same time? It's a good question.

Let's go on and look at some of the extrinsic causes. 66text3S.jpgThere was an argument for awhile that was quite viable, that larger organisms could not evolve until there was sufficient oxygen available in the atmosphere and most of that came from photosynthesis through cyanobacteria and the algae that existed at the time, and that once everything got oxidized on the surface of the Earth, then free oxygen would accumulate in the atmosphere. That took 4 billion years to happen. So at 0.54 or 0.55 billion years, there was sufficient oxygen around for the radiation of these organisms and making skeletons. A number of other ideas are here as well that we can talk about but that in fact can be dismissed. They all may be linked in a some way, so that although I'm laying out hypotheses here, in fact they all may be related to one another in some big scenario. The one that I particularly like, perhaps because I like to work in the oceans, is an oceanographic scenario that has to do with the production of nutrients in the upper part of the ocean waters, the euphotic zone where sunlight is available to the primary producers. These producers were the algae I showed you pictures of and, surely, lots of others were there too that did not preserve. This kind of production of the primary producers would be able to transgress through all ecosystems and cause all organisms to respond to the flow of trophic (food) resources and energy through different ecosystems. If you can come up with a hypothesis like that, that would account for all of these things, I would be much more satisfied with it than a strictly metazoan-bound hypothesis because that's too limited.

I want to point out that we really don't know the answer to the problem that I'm addressing. Paleontologists use a number of different methods to study these various problems. I have some ideas about how to attack it. One, of course, would be the molecular route; another would be to go and look for more fossils. But I would like to go to this place, 67caveS.jpg Palau, near the Philippine Islands, and study an analogous situation in the modern environment. Maybe it will tell us something. Palau is a raised island group. In the Miocene, only 15 to 20 million years ago, this used to be a reef and it's been lifted up. As you know, if you lived in Florida, when you uplift carbonate rocks, like those forming the ancient reef, rainfall tends to dissolve it and form sink holes, caves and other things. In Palau, 68lagoonS.jpg big sink holes form in the centers of the islands like this one, which is about 400 meters by 100 meters, and there are cracks through the limestone into the open ocean. This hole filled up and became a marine lake. But it's really a unique marine lake. 69jelliesS.jpg It's filled with 1.6 million jellyfish. These jellyfish, called Mastigias, have symbiotic algae in their bells; so they track the sun because those symbiotic algae photosynthesize and supply the animals with all the energy they need. This big wall of jellyfish is because trees shade this part and the jellyfish don't go into the shade. They need the sun for their symbionts.

70jellies2S.jpg The jellyfish are just everywhere, and that's about all there is in this lake except for a few other interesting things that I want to show you. 71diverS.jpg Here's me for scale so you get an idea of how big these things are. But there are some other things in this lake. This is a marine lake; there may be 150 species of a group living outside the lake on the open ocean whereas there are only four or five in the lake itself, like foraminifera. 72anemonS.jpg One of the groups are sea anemones. They live on the rocks and on logs that have fallen in and they catch the jellyfish and eat them as they go by. There are two kinds of jellyfish: Mastigias which lives in the upper part of the water column because it needs to photosynthesize with its algae and Aurelia which lives deeper down, down to about 45 feet. Look at this bottom. Wow, that's what gets me excited. 73jellyS.jpg That's an algal mat living on the bottom. It's all cracked up, it's loaded with bacteria. This is beginning to look like the sediments and the fauna that we see in the Vendian rocks on the White Sea. At least it's tempting enough to go and say let's study this. How did the jellyfish or do these jellyfish ever get preserved? What role did the bacteria play? What kind of preservation do the bacteria have for themselves? We can use a modern study to get at that question of what's going on, we hope.

74bactS.jpgThere's another interesting thing about this lake and that is at 45 feet in depth, as you dive down, you come to a layer of bacteria that's floating in the water column of the lake. The lake is 90 feet deep. So below this layer of bacteria, which absorbs all light and just completely eats up anything that falls into the lake, below it the lake is anoxic, no oxygen at all. It's hydrogen sulfide. You dive down there and then come back out and you smell like eggs, rotten eggs for a couple of days. So you have to be sure you dive with your friends or you won't have any. Now I'm trying to think about getting people like Stan who works on bacteria and people who work on the biology of the jellyfish and people who work on sedimentary processes and how fossils are preserved to go with me; maybe get one of these astrobiology grants from NASA, and say here's an analogous situation alive today that we can go and study that's not unlike what we see at the very beginning of the radiation of animals. Wouldn't that be wonderful?

Incidentally, astrobiology is the wrong term for this program, it should be astropaleontology. Just think about it, how are we likely ever to find a true astrobiological community out there other than ours. You have to hit them at exactly the right time. Most likely we'll find fossils out in space, I think. So it should be astropaleontology. What do you think, Stan? Let's go for it. So that's where we're going to go, I hope. Looking at molecular biology, modern situations, as well as reinterpretations and additional interpretations of existing fossils. The answers are not in, in spite of media like Time Magazine. And I'm sure NBC will get it one of these days!

Thank you very much.


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