Mega. Macro. Micro. Nano

It’s very easy in geosciences to get caught up with the details of whatever you’re investigating and forget the big picture. How does this strontium isotope ratio relate to the movement of the continents? After all, the history of the planet is what we’re trying to unravel, so I want to talk about the interconnectedness of scales in geology. 

Mega

The movement of continents over the last 4.54 billion years of Earth history is what I’m studying. But obviously the data to reconstruct this has to come from somewhere. You can’t just work backwards, as the continents have been arranged, made, and destroyed countless times before they got to how they are today. 

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This is a sketch map of relative geographic proximities before the Atlantic opened. I study the Caledonian rocks of Shetland, because they were pretty close to the Norwegian, East Greenland, and Scottish sectors of the Caledonian Orogeny. So it’s a pretty important little archipelago, up there in the North Sea. So a palaeotectonic map. How did that come into being? 

This is where scale becomes important.

Macro

We collected some rocks from Shetland with a sledge hammer. Typical outcrops look like this:

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Macro scale is really important in geology, as a lot can be told about how the rocks have behaved under temperatures and pressures. This outcrop has undergone a considerable amount of shearing, and a direction of movement can be extrapolated from this. Cool, huh?

Micro

Every geologist loves a good thin section. They’re pretty, have cool colours and the micro-textures you can see in thin-section are just as important as those seen at macro scale. 

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This is the thin-section of the rock collected from the above outcrop. It beautifully illustrates how the textures can be seen at different scales. I even photographed it in the same orientation to highlight this! 

How does this relate to the nano scale? Well, notice how the brightly coloured mica grains are touching the grey coloured feldspar grains? That suggests that at the time this rock was cooling, the isotopic systems will have been in equilibrium, which is really important when thinking about isotopes and geochronology.

Nano

This is where I start to get overly excited. Not unlike the ions I measure. bad geochemistry joke, I’m sorry (I’m not sorry). 

0.732917 ± 0.000010

The question is, how do you get down to the nano scale? Well, we measure isotopic ratios. Which is what the above number is, actually measuring ions that have been deflected through a magnetic field! How cool is that?

But whats the point? 

Measuring isotopes means you can calculate the age of rock and how it fits together with other rocks in the grand old scheme of things. Bringing us back to the mega scale of how the continents fitted together hundreds of millions of years ago. 

This is the reason geology is cool. You have to draw ideas from all over to see the bigger picture. But being able to piece together how the Earth looked millions of years ago, will never cease to amaze me. 

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Geologists find cool rocks wherever they go. Fact.

The well documented fact that geologists are good at finding interesting rocks wherever they go, isn’t just a function of them being good at it. It’s because there is interesting geology everywhere. Even in a city. All you have to do is open your eyes and notice it. 

Since becoming a geologist, I can’t go anywhere without finding something cool and worth a picture/sample. Which inevitably leads to my phone and pockets being full of rocks most of the time… 

For example, I was in Spain last week visiting family and when we were happily strolling along the promenade, I glanced down at the flood defences and saw this:

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I happily explained to my sister, her husband and their children that these ‘markings’ meant immense pressures, that make mountains. My two nephews were very excited at the idea of rocks behaving like a block of slightly melted cheese. Even my sister admitted she had never realised something that seemed so solid could act like that. 

Similarly, I was taking their dog Sandy out for a walk and found, amongst the seemingly endless limestone, a beautiful garnet-mica schist:

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Again, explaining to my nephews about what the different minerals mean regarding pressures and temperatures, and mountains, and volcanoes. 

We even found some fossils, and basalts. So for the rest of the trip they were picking up stones and asking me to tell them about them. The fact that they were so excited to have learnt something about the place they live that they had never known before really made me excited. 

Just goes to show though, geology is all around us. We just have to know what to look for. And that is really exciting. 

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Geochemistry using the 1000 most common English words. Not all that easy!

I finally accepted the challenge, and I have to say, it was harder than I thought it would be! They wouldn’t even let me ‘measure’! Well, here you go:

I study when rocks were formed, by looking at the bits of matter that make up the rocks and how they change over time.
To do this, I fire the small bits of matter (from the rock) through a field and, by sorting how heavy or light the bits of matter are, I can tell how old the rocks are.
This is important because by learning about the past, you can tell that will happen later in the world, as it changes.

I like ‘firing bits of matter’ but I don’t think I made the applications very clear. At least I gave it a go! 

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Even geologists need to think about maths.

I’m the first to put my hand up and say that until very recently, I had a near crippling fear of maths.

But as a scientist, I needed to bite the bullet and learn my shit, because I don’t want to be one of ‘those’ geologists who can’t be taken seriously because they fail to grasp the basic principles of maths.

However I’ve been getting more and more irked by reading geochemistry papers where the authors are proposing trends in isotopes/chemistry that areactually just a function of pure good-old-fashioned mathematics!

For example:

Screen Shot 2013-01-15 at 21.14.45

A paper in which an un-named, but very eminent geochemist has shown a trend, which he suggests is a function of sediment being incorporated into the melt of a subduction-related arc lavas.

Seems reasonable, right?

NO!

I’m sure you’ll notice, as I did, that the denominator of the y-axis is the same as the x-axis.

So essentially, this is a graph of 1/x vs. X. Such as this examples I just made in Excel (Where X=n*2):

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Wow, a hyperbola! What a surprise!


It’s not a geochemical insight if it’s a function of maths. So it’s important to think about the maths before talking about the geochemistry.

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Introductions are the normal thing, right?

I’ve finally taken the plunge and started a ‘proper’ blog. I’ve had twitter and tumblr for a while, but they don’t really suit my needs for a platform to show my love of geology, and allow for the occasional vent about things I don’t think are quite right.

Hammer For Scale will mostly be about being initiated into the science community as a student and graduate. (Hopefully in my case a grad student, so fingers crossed!)

There are some really fantastic geology blogs out there and I hope my contribution to the geoblogging sphere won’t disappoint!

Steph.

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