This episode explores how the soil and geology of the Lake Mungo area tells the history of this area for the last 60000 years. The video explains how the plant life has adapted to the soil and climate conditions. Viewers will see different and easy to do experiments to test soils and gain an understanding of the meaning of the results.

Soil and geology (13:58)

Episode 13 – Soil and geology

Warning – Aboriginal and Torres Strait Islander viewers are warned that the following video may contain images and voices of deceased persons.

(Calm music playing)

Daniel – [Daniel Rosendahl, Executive Officer, Willandra Lakes Region World Heritage Area] The World Heritage Area is listed for its unique geological features, which can help us recreate environments from about 150,000 years ago through to the present.

Harvey – [Harvey Johnston, Archaeologist, NSW Office of Environment and Heritage] so, the lunettes, has a series of layers in it that are built up from sand being blown up to the Eastern side of the lake when the lake was full of water. And then when the lake waters dropped and you had a large clay pan clay from the lake floor being deposited into the dune. So, the sedimentation of the dune on the Eastern side of the lunette is made up of alternating clay rich, sand rich, clay rich, sand rich layers and they inform us about wet conditions, dry conditions, wet conditions, dry conditions. So, the geology tells us about the whole Australian climate.

Ivan – [Ivan Johnston, Discovery Ranger, Mungo National Park] Just below us, we got four, four layers of soil at the bottom layer of soil layer known as the Gogol layer of soil. That's very old. We also got the middle layer soil which is the red colour soil, that’s known as the Mungo layer of soil. further up top, the Zanci layer of soil. Each of these layers of soil, we have found extinct animal bones, and also stone tools and all fall places in these layers of soil.

Amanda – [Amanda Ritchie, Science teacher, Southern Cross school of Distance Education] And what is the idea behind the wet conditions, dry conditions? Why was that happening? Why is there clay, sand, clay sand, clay sand.

Harvey – The global climate has gone through a whole series of fluctuations, waxing and waning, some, some major cold phases. Ice ages. Extremely cold and extremely dry and some very warm phases that's been happening forever, really, that climatic change. And so, we are looking here at a pattern, a short period, geologically 40 or 60,000 years in the Orlando, and just looking at that little time. And so, we've got a lake full face at 40,000 wet conditions. And then the lakes dry as the world climate gets colder and more and more of the globes water gets bound up in ice sheets and Glaciers. Sea levels fall and it's just not available water. And that cycle is gone again and again.

[Screen reads: Soil tests with Amanda Ritchie]

Amanda – Hello everyone, I'm standing here at the side of lake Mungo. My name's Amanda Richie, and I am a science teacher at Southern cross DE. And you can see the beautiful landscape, high, vast, and expanse it is. the mean vegetation is Salt bush cause it's really the only type of plant that can survive in this arid environment. Therefore, the flora and fauna need to reflect that and adapt to live here.

[Screen reads: Types of plants are closely linked to soil and geology.
We tested the soil at Lake Mungo to see what we could find out.
Soil test 01 – PH test for soil type 1]

What I'm going to do is, do a very short simple pH test of some of the soils that we find at lake Mungo. so, you can see here today, the soil that we're on is very, very sandy.

[Screen reads: Fact. Soil characteristics are fine, light, granular and sandy soil]

Okay. It's very appealing colour. And it's very small greens and very, very fine. And we can do a very simple test to test the PH of this soil using universal indicator from my little kit and something called barium sulphate and that just helps show up the colour of the indicator.

[Screen reads: Fact. Universal indicator shows if a material is acidic or alkaline by changing colour]

So most soils range from acidic to alkaline, and that really does affect what grows in those soils. And you might remember acids and alkaline, and you might've seen this universal indicator chart before. so, if the indicator is dark red indicates that soil is very acidic or something's very acidic. Acidity lessens as you go through the colours from red, orange and yellow green means neutral. And the other end of the scale is towards alkaline so, if the indicator turns like deep purple or blue, that indicates a lot of alkalinity in this soil.

So let's test a small sample. so, we have a little white porcelain tile. I'm just going to scrape some of the soil into there.

[Screen reads: Fact. The indicator pipette should not make contact with the sample. It contaminates the universal indicator and you can no longer use it]

And the next thing we want to do is just add a few drops of the universal indicator. And as I said, that's an indicator that will change colour depending on the acidity or alkalinity of the soil. As you can see already it is turning a green colour. Okay.

[Screen reads: Question. What does a green pH reading mean?]

And if we use our chart before we put our barium sulphate on, you can already see that it seems to be indicating somewhere between pH 7 pH 8. Okay. so, pH 7 is neutral pH 8 would be slightly alkaline, so, it's been wet. And now with the universal indicator we just need to add a light dusting of barium sulphate.

[Screen reads: Fact. Barium sulphate (BaSO4) reduces the colour change created by soil particles that can cause an inaccurate pH reading]

I'll use the other end of the spatula. And just sprinkle a little bit of barium sulphate that just helps the colour of the indicator to come out. And mix that together. (Playful music) See it's changing slightly lighter green with the barium sulphate. All right.

[Screen reads: Question. What does the indicator turning lighter mean?]

This just helps to minimize the colour impact of the other minerals in it. So, if we compare it to the indicator paper, I know it looks quite dark on the universal indicator chart, but it is very much green. so, at the moment, without any further tests, we would say that this sandy soil is a mainly neutral soil if slightly acidic or slightly alkaline, sorry, according to our tests. And that's it for a simple pH sample of this soil.

[Screen reads: Fact. Sandy soils are often acidic and chalky and contain calcium carbonate which are often alkaline. so, we could infer that this type of soil is a mixture of sand and calcium carbonate soils.]

[Screen reads: Soil test 02 – How to test your pH kit]

Amanda – Hello everyone. just want to show you how you can test if the universal indicator is in fact indicating if a soil or a liquid or something you're testing is acidic, alkaline or neutral. Okay. And what you really need to do is get something of known acidity.

[Screen reads: Question. What household items are acidic? What are the characteristics of acids?]

Even if, you know, if it's acidic or for example, water should be neutral, especially distilled water and or something alkaline like detergents or bleaches or something like that.

[Screen reads: Question. What household items are alkaline? What are the characteristics?]

So, to show you very briefly, I have hydrochloric acid here that was in my soil testing kit.

[Screen reads: Fact. Acids are compounds that contain hydrogen in a form that is released when put into water. pH is a relative measure of how many hydrogen ions they release]

So, I know that that should be acidic and using a universal indicator. And according to my chart, I would expect it to be towards this end of the spectrum. so, definitely orange, if not very red, because it's very high in acidity.

So, all I do is I have my porcelain tile I previously used this section to test a bit of the Sandy soil in this area. All I need is one drop of HCL, hydrochloric acid, and one drop of universal indicator. Makes sure the end of the pipette does not go into the solution or it will contaminate your entire bottle of universal indicator. so, you just drop it from above and you can see it very quickly turned an orangy red colour. And according to your universal indicator chart, that shows it's a very strong acid.

So, our universal indicator is working correctly and therefore from our previous samples, we can trust the colour of the indicator. Okay. so, that's a top tip when you're doing some tests on pH Thank you

[Screen reads: Soil test 03 pH Test for soil type 2]

Amanda – Hi, everyone. Just going to show you another Ph test a slightly different soil type.

[Screen reads: Fact. Soil characteristics: sandy, fine, light, red]

So, this soil is still very sandy based. It's very fine, very coarse, very light, but slightly different in colour. so, we're going to do same as we did before. We just need a small sample into the porcelain tile, we add one or two drops of universal indicator. Make sure that the pipette does not touch the soil because we don't want to contaminate the dropper.

[Screen reads: Fact. The main components of a universal indicator, in the form of a solution, are thymol blue, methyl red, bromothymol blue, and phenolphthalein.]

The soil is very dry, so, I'm just adding a few more drops to let it soak in now you can see it's went a deep green type of colour. And now we haven't added our barium sulphate onto it yet. Ill add a bit on, there's a little ant trying to get in on that action. You can see already if it's in the green section, we’re presuming it's neutral. If not slightly alkaline.

All we need is a light dusting of barium sulphate. Try and mix it through a little. The barium sulphate is just absorbing some of the universal indicator and, trying to reduce the impact of the colour of the soil on the colour that it's indicating.

You can see it has changed colour quite dramatically from a deeper green more to a yellowy green. See sometimes it can be quite difficult with the colour of the soil to truly reflect the PH so, really, it's lightened up that deeper bluey green. And it's more, it's quite difficult to see, but it's more of a yellowy green, really. so, for me, this is indicating that it is neutral, but almost slightly acidic possibly, but in order to make any firm conclusions, I would suggest that we repeated this a couple of times to improve reliability, but that's what the results show us.

[Screen reads: Fact. The most accurate common means of measuring pH is through a lab device called a probe and meter, or simply, a pH meter

Soil test 04 Sediment composition]

Amanda – Hello everyone. What I did with a sample of soil was I added distilled water to a small sample of soil so, that we had a, we call it a two to one ratio. so, we've got about two sections of water to one section of the soil sample. And I shook it up once the lid was on and allowed it to settle. And hopefully what you'll be able to see is we're looking at how the sediment has settled down at the bottom. so, this is all just cloudy water. We're not that interested in that, but what you might see is clay will settle at the top.

[Screen reads: Fact. Sediments settle according to their size and weight]

So, you can see this deep grey clay at the top. And then you can see the rest of the sediment looks quite like sand, and we can use this to work out rough estimates of the percentage of clay to sand.

[Screen reads: The sand-clay sediment layers provided the conditions suitable for fossil formation]

And that can tell us about, the sandy soil, and it can indicate what might be able to survive there. What other minerals are in the soil, et cetera. so, that's another test, simple test that we can do

[Screen reads: Soil test 05 Carbonates]

Amanda – Hi, everyone. I just wanted to show you a simple test for carbonates.

[Screen reads: Fact: Carbonate minerals are those minerals containing the carbon ion]

What I have is a sample of sandy soil in a small test tube. I added two thirds of water to it and shook it up and allowed the sediment to settle. And I just decanted off the water at the top. And the test for carbonates is to add hydrochloric acid. so, I've got hcl.

[Screen reads: Fact. Carbonate + Hydrochloric acid = Carbon dioxide + Water + Chloride]

We want a two to one ratio. So, we want to apply twice as much acid to the soil. And we're going to say if a reaction occurs. so, we expect some fizzing and the more fizzing and the faster, the reaction suggests that there's a higher level of carbonates in the soil. And vice-versa so, if there is a much reaction, that's okay. There just isn't many carbonates present. so, we're going to add the hcl

You can see, I don't even need to add the two to one ratio. We've got evidence of a reaction. I can hear bubbling. I can see bubbles forming it's fizzing. so, what that tells us is there is in fact carbonates present in that sandy soil sample.

(cheerful music)

List of sources and acknowledgements

  • Image: Lunette formation from 40,000 years ago to present. Source provided by Professor Jim Bowler

  • Video: Forces shaping Willandra Lakes. Provided by National Parks and Wildlife

  • Image: Water level curve of Willandra system spanning 50,000 years. Source provided by Professor Jim Bowler

  • pH Scale facts. Facts about what makes a substance acid and what the pH scale measures can be found here

  • Narration. Voice over by Amanda Ritchie, Southern Cross School of Distance Education.


NSW Government Public Schools, Learning Systems, DART connections, Southern Cross School of Education. Virtual Excursions 2017.

End of transcript

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