Grand Canyon: Granite Rocks

As a geology student I love to look at, touch, and think about rocks.  However, I am afraid that I do not love all kinds of rocks equally.  My least favorite rocks are the ones that look like pieces of dinosaur bones and other fossils  – “Oh, it’s just another rock”.  On the other hand, I also have an all-time favorite type of rock, and that is granite.  The first thing that most people notice about granite is it’s beauty, displayed in it’s unique depth of colors and textures.  Next, people usually notice that it’s a pretty tough rock.  The combination of these two reasons is why granite is frequently used in stylish kitchen counter tops, elaborate government buildings (like a state capital building or county courthouse), and grave stones and other monuments.

I appreciate granite for it’s physical beauty just like anyone else, but perhaps a bit more than your average granite admirer because when I look at granite, I look for the things that remind of it;s intellectual beauty as well.  Last week, we discussed a little bit about rock dating in the Grand Canyon.  Today we will explore the specific rock dating in the granite of the Grand Canyon.  Don’t worry though, I will not make it as intimidating as it may sound.  Granite is a rock.   Rocks are a conglomeration of several minerals.  The next time you see granite, take a deeper look at it, and see if you can find the minerals I’m telling you about in it. Granite is made of three minerals: Quartz (which comes in several different colors), feldspar (usually a creamy gray or peachy color pieces) and biotite (black or green).

The biotite is the key to radioisotope dating in granite.  Biotite comes in tiny thin sheets of plastic-like material, all staked together.  I have tried to pull apart bioitite sheets to get just one sheet to look at under a microscope, but I can’t really say I succeeded, because these sheets are so incredibly thin and stuck together.  Radioactive Uranium is trapped in tiny crystals between the sheets of bioitite.  Because this Uranium is radioactive, it shoots out tiny pieces of itself suddenly, which damages the delicate biotite sheets, leaving a series of rings around the original crystal that the Uranium was stuck in. Taking the layers of biotite apart, it ends up looking like onion slices.  These rings (called raiohalos) are so tiny that three of them lined up would be about as thick as a single human hair.

We are often stunned by the vastness of the Grand Canyon, thinking of how marvelously it shows God’s mighty power.  Yes, the big things of the Grand Canyon do show the glory and truth of our incredible Creator, God, but the little things do too.  Tiny radiohalos, simple marks in the millions of layers of a little black speck in a rock, speak of God’s judgement in the flood and the truth of the Bible from the very beginning.  Normal Uranium decay makes eight rings, but many radiohalos have been found with just one, two, or three rings.  By measuring how big these rings are, we can know that the step of radioactive decay that made these rings happen very fast,  but they have to start out as Uranium and go through millions of years worth of decay first.  This means that the granite had to have still been soft and probably have water flowing through it  after millions of years worth of Uranium decay happened.

So what does it all mean?  It means that radioactive decay has happened faster in the past (during the flood) than it does today.  In other words Radioisotope dating is not as simple or consistently reliable as scientists have thought and the Bible is right about the age of the earth and Noah’s flood.  We can’t completely trust Radioisotope dating, but we can put our trust completely in God and His Word.

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