Lecture: Cambrian Explosion: Narrator: Listen to part of a lecture in a geoscience science class. Professor: Okay any more questions about plate tectonics? Female Student: Yeah. I noticed that, our textbook readings seem to imply that plate tectonics played a big part in the evolution of some of the earliest complex life forms. Professor: They only implied this because the connection between plate tectonics and early evolution isn't very well understood yet, but there are a lot of hypothesis and a couple of new ones are very interesting. Male Student: Is there any time to talk about them today? Professor: Sure I can do that now, but we need to begin with what's known from the fossil record. The fossil record indicates that there was a huge increase in the kinds of organisms that live in the earth continents starting around five hundred and thirty million years ago, um, when there used to be only simple life forms, then quickly emerged a wide variety of complex multicelluar forms. Um, this time period five hundred to six hundred million years ago, it's called the Cambrian period which is why we call this proliferation of new species, the species diversification, the Cambrian Explosion. Now one pretty intriguing and I think quite logical scenario to explain all this has been proposed by group of Australian researchers a few years ago. They believe that the Cambrian Explosion was probably fueled by a massive influx of nutrients into the ocean. Nutrients as you know, are substances that organisms must have in order to like iron calcium potassium and so on. And this idea makes sense to me because, anytime in Earth's history, when there was a rapid increase in new species, it's always associated with an increase in availability of nutrients of food. Female Student: So what caused the influx during the Cambrian period? I mean where did all the nutrients come from? Professor: Well according to the hypothesis, the source of the nutrients was a gigantic mountain range, the erosion of a gigantic mountain range I should say. The researchers called this mountain range the Gondwana Supermountain. The Gondwana Supermountain would be in Gondwana, a super competent in the southern hemisphere made up of present-day America Africa India Australia and Antarctica. The Gondwana Supermountain formed during the early Cambrian era by "formed". I mean plate tectonics caused smaller continents to solely crash into each other, to create one giant continent and stresses of the collisions could form the Gondwana Supermountain. Female Student: So that how the Himalayan is got lifted when India crashed to the Asia? Professor: Southern Asia, right. And that's the beauty of this hypothesis. It is based on currently available geological evidence. So imagine this giant mountain range, eight thousand kilometers long and a thousand kilometers wide, the largest ever near the equator weathering and eroding. Remember that weathering refers to the breakdown of rock into soil, primarily by physical and chemical forces that occurs most quickly in the tropics where the heavy tropical rainfalls would carry countless tons of the weathered supermountain and all that nutrient-rich soil within it downhill into the ocean. Male Student: So how about those nutrients get into the food chain and and affect species diversification? Professor: They would have first been absorbed by simple marine plants like algae, then by the microorganisms that ate the algae, and then by the larger organisms that ate the microorganisms and up on the line. At each level populations were quickly expanded, diversified and in just five to ten million years evolved into, increasingly complex species. For example with infusion of calcium and molecules containing calcium we get the widespread appearance of the first shell animals and first animals with skeleton, to develop in a range of species. Female Student: But what evidence does these researchers in Australia have to prove that the Gondwana Supermountain naturally exists? Professor: Well there are certain sandstone deposits in the southern continents. Remember sandstones are very common sedimentary rock made up of small particles of rock remnants. Um, the sandstones as the researchers collected contain a variety of minerals including Zircon. Male Student: Zircon? That's not a nutrient is it? Professor: No, but Zircon is important to the hypothesis because it can be dated. The age of Zircon samples collected in Australia, closely match those in the Zircon samples from Africa and India and from other continents that were once part of the Gondwana. This similarity in age suggested that Zircon crystals and sandstone deposits that were found all erode from the same source, the Gondwana Supermountain.