Our Changing World
Thursday 26 February 2015, with Alison Ballance, Ruth Beran & Veronika Meduna
On This Programme
- Time Travelling through Mead Stream Gorge
- Unlocking the Secrets of Photosynthesis
- Using a Scanning Electron Microscope
- New Zealand Dotterels on Great Barrier Island
Time Travelling through Mead Stream Gorge
by Veronika Meduna
'In this area, the gorge cuts through a sequence of rocks that span the entire geological history of New Zealand from about 90 million years ago right through to the present day.' _James Crampton
Mead Stream Gorge, about halfway between Blenheim and Kaikoura, is one of New Zealand’s geological wonderlands.
Geologists come from all over the globe to study the exposed rocks and the gorge is possibly the only place in New Zealand where you can travel through 90 million years of geological history in one day.
Geologists and paleontologists from GNS Science have led field work in the gorge for several decades, working closely with the Murray family, who own Bluff Station inland from Kekerengu on the Marlborough coast.
Paleontologist James Crampton says the gorge is one of the most accessible in the region, but also represents the most continuous geological record, spanning from the slow drowning of the Zealandia landmass following its split from Gondwana, through the geological boundary that marks the demise of the dinosaurs, and on to a period of mountain uplift that continues today.
'The rocks lowest down are from a time when there was still tectonic movement going on and New Zealand was breaking off Gondwana, splitting away and drifting into the South Pacific by continental drift. Then, for a long time there was no tectonic activity and New Zealand gradually sank.'
Further up the gorge a layer of huge boulders provides evidence for the start of a new tectonic phase and mountain uplift when the Alpine Fault formed, about 25 to 35 million years, and finally, right at the top of the gorge, is the active Clarence Fault, one of the country’s fastest moving faults.
One of the significant – albeit perhaps least obvious – sightseeing stops in the gorge is the geological boundary layer that marks the end of the Cretaceous epoch and the extinction of the dinosaurs, together with about half of all other creatures that lived at the time.
It was the second largest extinction event of all times, but all that remains of it today is a thin dark sliver of clay, measuring a few centimetres, that marks the moment when a meteorite hit Earth and covered the planet in dust. This layer is commonly known as the K-T boundary (T stands for the Tertiary, and K comes from Kreidezeit, the German term for the Cretaceous).
Chris Hollis, at GNS Science, says the K-T boundary at Mead Stream was very difficult to pinpoint, and represents one of only two places in the world with an unusual signature of the meteorite impact. Two types of evidence usually identify the boundary: a high level of Iridium (an element that is extremely rare in the Earth’s crust, but abundant in most asteroids and comets) and the sudden extinction of microscopic organisms called foraminifera, or forams for short. “This Iridium anomaly in this case is found only in the burrows in the top of the Cretaceous,” he says.
'What’s happened is that the meteroite hit the Earth, the dust cloud enveloped the planet, the Iridium-rich clay settled down through the oceans, fell on the seafloor, filled the burrows and all the things inside the burrows died. Then it was swept clean by some current, possible a tsunami from the impact that swept the surface clean so there’s only normal clay deposited afterwards and all the Iridium, all the evidence of the impact, is actually in the burrows in the top of the Cretaceous.' _Chris Hollis
Further up the gorge, a layer of conglomerates – rocks that are made of lots of cobbles and pebbles – signify the beginning of a new period of tectonic activity and mountain uplift. James Crampton says this marks the instant when the modern plate boundary and mountain uplift started in this area. “Tectonic activity suddenly switched on here, mountains started going up really fast and eroding, and all this gravel was falling into deep water off the edge of the mountains – exactly what’s still happening off Kaikoura today with the Kaikoura Canyon.”
Right at the top, GNS Science earthquake geologist Russ van Dissen studies the Clarence Fault, one of a cluster of active faults that branch off the Alpine Fault and trend northeast through Marlborough and towards the North Island. “It’s one of the four big faults of the Marlborough fault system,” he says. “This fault zone transfers the motion from the subduction zone in the North Island, and as we move south these four faults distribute the strain and then all that gets dumped down onto the Alpine Fault further to the south and on the west coast of the South Island.”
The Clarence Fault moves about five millimetres per year and is one of several fault lines Russ van Dissen studies in an effort to piece together the region’s earthquake history. He says the Clarence Fault has produced large earthquakes in the past, on average every 2000 years, with the last one about 1700 years ago. “If we do that for all major faults … that all gets put into the building code. One of the outcomes of the work we’re doing here is how to prescribe the appropriate earthquake loadings for buildings.”
The team also explored a layer that represents the Paleocene-Eocene Thermal Maximum, or PETM. During this episode, some 55 million years ago, the Earth warmed rapidly and went through a major climate change and extinction event. Our Changing World will feature this part of the research next month.
Unlocking the Secrets of Photosynthesis
By Alison Ballance
“From my perspective plants are machines that capture light. And they’re able to take light energy and turn it into chemical energy, and use that process to extract carbon dioxide from the atmosphere and generate sugars. So leaves are factories turning solar energy into food.” Julian Eaton-Rye
Julian’s work focuses on the water splitting process, which happens in Photosystem II, near the beginning of photosynthesis. “What’s remarkable about that process,” says Julian,” Is that if you want to do that yourself, you’re going to have to heat it up to about 2000 degrees Centigrade, because you’re breaking it apart – and water is phenomenally stable. So to break it apart is a thermodynamic challenge, and Photosystem 2, this first step in photosynthesis, has evolved just once in evolution – about 2.5 billion years ago – to split water and use this abundant source of material as a fuel source to drive the biosphere.”
Julian uses the cyanobacterium Synechocystis as his model plant, and his research focuses on proteins and how they are constantly broken and repaired.
“The chemistry of Photosystem 2 is so challenging that it actually damages the enzymes as it operates normally,” says Julian. “So there’s this cost, that to use this wonderful source of energy the protein structure actually damages itself and needs to be repaired.”
Julian believes that if we can understand how this protein repair mechanism works, it could lead, for example, to more efficient photovoltaic panels – at the moment these have a limited life, but Julian believes it should be possible to greatly extend this.
Another result of understanding the water splitting process could be the creation of low temperature water-splitting technology to produce hydrogen as a source of fuel. Modifying plants so they can better survive in arid environments, or hot and cold environments, is another possible outcome that could lead to better food production.
Using a Scanning Electron Microscope
Materials engineer Dr Ruth Knibbe uses a scanning electron microscope (SEM) to image her own samples and samples for other scientists. Unlike a light microscope, an SEM uses a focused beam of electrons to produce images from the top surface of a sample. “So you don’t get lots of information from the bulk of your sample, it’s mostly topography that you’re getting information from,” says Knibbe, from Victoria University of Wellington.
An SEM can also be used to extract analytical information. “So you can also find out what atoms…or what elements you have in your sample,” she says. For example, whether a sample contains iron or oxygen.
The electron beams in an SEM come down a column, and when it hits the sample will either release secondary electrons or back-scatter electrons. Secondary electrons provide information about the topography of a sample, and the back-scatter electrons provide information about the composition of the sample, otherwise known as atomic number contrast.
The electron beam in an SEM is very finely controlled, and starts in the top left hand corner and moves quickly across the sample in a rastering format. Electrons from that particular area are detected which creates a signal.
“That’s why we call it a scanning electron microscopy detector…because you’re actually scanning across that surface,” says Knibbe.
So unlike a light microscope where the entire sample is saturated immediately, an SEM scans across a sample and every location gives a slightly different signal.
Samples generally need to be conducting, so non-conductive samples such as geological or biological samples are coated with a metal or carbon. “If you have an insulator, it would just flare up and charge and you just see lots of bright white. Not so interesting,” says Knibbe.
Samples are loaded onto circular stubs which have a pin underneath which can be tightened into the microscope with an Allen key. “You don’t want your sample to be moving when it’s in the microscope,” says Knibbe. “If it’s moving in the microscope and you’re imaging it 100,000s of times, you’re not going to see very much at all.”
Different scientists use an SEM for different purposes. “[Biologists] would use this microscope because you can get that high detailed topography information,” says Knibbe. Another big benefit of a scanning electron microscope for all types of scientists, as compared with a light microscope, is the huge depth of field which gives SEM images their characteristic, almost 3D-like, quality.
You can listen to an extended version of using a scanning electron microscope here:
Using a Scanning Electron Microscope - long version ( 31 min 24 sec )
You can listen to the on-air version of the scanning electron microscope story below:
New Zealand Dotterels on Great Barrier Island
By Alison Ballance
“So the problem is one of getting the community behind the eradication effort, and they would have to be 100% behind it. And if that was the case I think it would be possible. Expensive. But possible.” Botanist and island resident John Ogden on the idea of eradicating pests from Great Barrier Island.
The story of Awana Bay’s family of New Zealand dotterels is worthy of a TV soap opera. Retired botanist John Ogden lives nearby on Great Barrier Island and he has been watching the saga of the dotterel pair unfold all summer. First of all, as he tells it, the pair laid an egg in a scrape on the beach just above the high tide mark. Someone else noticed it and reported it to John but by the time he went to investigate the egg had been abandoned. John thinks the person got to close to the nest and scared the parents away, leaving the egg exposed to the hot sun.
The dutiful pair then renested nearby, and then, says John “And this is most remarkable and unbelievable thing. And it’s true. A pair of oystercatchers took over the second nest, and began to incubate the dotterel egg.” Meanwhile the dotterels returned to their original nest and laid another egg, alongside the original dud egg. Then just before Christmas a storm washed away both nests. However after the storm someone saw a dotterel chick on the beach near the estuary, and although John never found it he thinks the second dotterel egg must have hatched just before the storm hit.
The pair of dotterels then nested again, and by early January had a third nest with three eggs in it. John was keeping an eye on it and then just before the eggs were due to hatch there were four very high tides in succession. One tide even lapped around the nest, until finally strong southerly winds combined with another high tide finally washed the nest away. John thought that was the end of the pair’s breeding hopes, until the day before Alison Ballance joins him for a walk, when he notices a tiny dotterel chick running about. John says it must have hatched between the two last high tides, but the other eggs weren’t so fortunate.
As well as carrying out counts of New Zealand dotterels around all the beaches on Great Barrier Island, John, who used to work at the University of Auckland, also monitors his local population of pateke or brown teal, and is still involved in research into vegetation succession on the island following disturbances such as fire.
For many years he was Chairperson of the Great Barrier Island Environmental Trust, and he has been advocating to make Great Barrier Island pest-free. Great Barrier Island, which lies 100 kilometres from central Auckalnd, on the eastern side of the Hauraki Gulf, has ship rats, mice, pigs, rabbits and feral cats, but it does not have possums, hedgehogs or mustelids. Although he says it would be expensive to rid the 285-square kilometre island of pests, John says it is technically possible. The biggest challenge is to get the island’s population, which numbers nearly 1000 people (some permanent residents plus off-island residents with holiday homes) to agree to the plan.
Coming Up on Our Changing World on Thursday 5 March
Seaweek stories on rig sharks and eagle rays, e-cigarettes, and Te Punaha Matatini, a Centre of Research Excellence focusing on complex systems.