Category Archives: Geological Principles

Jökulsárlón

As promised, here is another post from my Iceland trip.  This time it’s of Jökulsárlón.  To be honest I don’t know why this place isn’t better known.  For me I think it’s one of the natural crown jewels of Europe, nevermind of Iceland.  Basically Jökulsárlón is a semi-tidal lagoon on the south-east coast of Iceland and formed in the 1930’s by the retreat of Breiðamerkurjökul.  Breiðamerkurjökul’s moraines formed the edge of the lagoon and there is a small tidal river connecting the lagoon to the sea.  But what for me makes this place so special are the icebergs.  Breiðamerkurjökul carves the icebergs which then float around in the lagoon, slowly melting.  Some of them do make it down the small river floating out to the sea, but also being pushed back by the tide and landing on the beach forming yet more amazing ice blocks on the black sand.  OK so that’s enough of me talking lets have some pictures.

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I think the one above looks a bit like a seal’s head.

DSCN3065The pictures really don’t do this place justice.  Maybe I just don’t get out enough but this is one of the most amazing places I’ve ever visited.  I probably will never get to go to Antarctica or the high Arctic, but this is pretty close.  This is one place that should be on a lot of peoples’ bucket lists and I’m glad to have ticked it off mine.

 

Noah Movie Part 1 – brewing up a storm

Here we go for another one of my ramblings.  A few months ago a movie based on the story of Noah hit the cinemas, and since then it has kicked up a storm and led to a flood of comments from all sides (OK I promise no more water-based jokes).  With the wave of criticism (sorry – another water joke) I thought I’d add my own thoughts, not so much of the movie but of the story of Noah itself and the comments that have been thrown up, but of the story of Noah itself.  I confess that I started to write this article months ago when the movie was first released.  As I started to look more into the subject it took me longer to work on it and eventually this post fell by the wayside as other things came up.  With the Noah movie being released on DVD I decided that I should really finish this article.  This article will be looking more at the story of Noah, and not so much about the recent movie.  As a little note, I have seen the movie and as a piece of cinema I thought it was OK.  The acting was good, the characters nicely developed and the special effects were of a reasonable quality.  It’s not the best movie I’ve ever seen, but it’s far from the worst.  But it’s not these factors that have caused the outcry from both the Christian and Atheist communities, but rather the story itself.  As a heads up this post is rather lengthy, so you might want to go to the bathroom now, get yourself a drink or light snack, but if you stick with it you will be rewarded with some pictures of cats ;).

The obvious religious connection has been the cause of most of the trouble.  From some atheist circles there has been criticism regarding the religious origins of the movie (for me personally this hasn’t been an issue, I see it as a good bit of story telling nothing more),  but I am aware that there are those who decry anything relating to a religious story being told in mainstream media.  The biggest complaints though are from those people who take the Bible a little literally.  From a number of religious groups the criticism is basically that the story is not true to that recorded in the Bible.  This in turn has led to atheists responding with comments to the effect of “you’re complaining that your made up story is even more made up?”  I have personally found these exchanges to be rather entertaining.  If you want to see some of them, just go on YouTube and search for something like ‘Christian reactions to Noah movie’ and you’ll see what I mean.  There has even been considerable effort made by Creationist websites such as Answers in Genesis to discourage people from seeing the movie and by posting material on their own site explaining how accurate to the Bible story the movie is.

As for me I am an atheist, though born & raised into a Christian family.  By atheist I mean that I do not believe in a god, but I am open to the possibility if sufficient evidence can be presented; this has not happened therefore I don’t believe.  I do own a copy of the Bible (King James version) and unlike most of the  Christians that I know I have read the thing from cover to cover.  The story of Noah is found in Genesis chapters 6-9.  So with this as a background I delve into the muddy world of creationist criticism.

Size of the Ark

This has always been a problem for both believers & none believers alike.  There have been some comments regarding the size, with one creationist claiming it had the capacity of about 500 railroad cars.  This led to a number of atheists crying “rubbish it’s not that big”.  Well of all the issues this is perhaps the easiest to resolve.  The bible measures the ark in cubits; 300x50x30.  The cubit varied in length over time but this leads to the ark being around 137.2×22.9×13.7m.  This gives the ark a volume of about 43,043.8 cubic metres.  The International Union of Railways (UIC) has standard sizes for goods wagons varying between 63 and 131 cubic metres.  Lets take a medium sized, 2 axle car which has a volume of 88 cubic metres.  This gives the ark’s volume of around 489 railroad cars.  So yes in a moment of creationist maths success the volume of the ark is about 500 railroad cars, depending on which size of car you use.

According to Genesis 6:16 the ark had three levels to it.  Could such a thing be built? Well yes & no.  We build ships bigger than this but in metal and there have been a number of people who have recreated arks albeit as tourist attractions rather than sea-going vessels.  Large wooden ships have all sorts of problems.  I refer you to the Wyoming (1909-1927) and the HMS Orlando HMS Mersey (both in 1858)which are amongst the largest wooden ships ever built.  They suffered severe structural problems from the wood warping & bending, seams opening and just a general strain on the wooden hull.  These problems could only be solved with steel & iron reinforcement.  All of these ships were smaller than the ark is suppose to be (by at least 37m).  Beyond the size and what type of wood to use there are no further instructions on how it was built, and as wrought iron working didn’t develop as a technology until at least the 1st Century BCE this lends doubt to the ark being real.  And before anyone asks about copper & bronze being used, these materials are too flexible for the kind of strength needed.  This is why iron swords replaced bronze ones.  Suffice to say it would have been virtually impossible for a an unskilled man to build a wooden boat of this size and have it work in what would be an almighty storm.

The Animals

Now here’s where things get interesting.  The traditional view is that the animals came in two-by-two.  Well this isn’t entirely accurate…welcome to one of the contradictions in the Bible – yes Biblical literalists the Bible is not perfect.  In Genesis 6:19 it says that “two of every sort shalt thou bring into the ark, to keep them alive with thee”, whilst Genesis 7:2 “Of every clean beast thou shalt take to thee by sevens, the male and his female: and of beasts that are not clean by two, the male and his female.”  So is it by 2’s only or 7’s and 2’s?  Next comes a second contradiction.  The laws given regarding clean & unclean animals are recorded later in the Bible (Leviticus 11) when God spoke to Moses…an event at least 700 years after the supposed flood.  This gives us two possibilities; 1) God gave Noah a description of which animals were clean & unclean that is not recorded in or has been lost from the Bible; or 2) clean & unclean was a later edition by scribes who altered the text.  Either leads us to one conclusion – the Bible has been altered by later peoples, which makes taking it literally a bit difficult.

Next I’d like to bring up the space for animals.  This is where it has taken me some time to write this post as I’ve been reading up animal sizes.  Here’s a list of some of the larger land mammals currently on the earth, their size and how much space of that 43,000 cubic metres they would take up.

Large mammal sizes 1I hear what you’re about to say “hold on 7 giraffes?”  Now I confess to not being an expert in the Rabbitic traditions & commentaries of the past 2,500 years so there may be an exception here, but I’m just using an English translation of the Bible.  As said the descriptions of clean & unclean animals are in Leviticus 11 and in the case of land animals if it is cloven hoofed and chews the cud (i.e. a ruminant) then it is clean if not then it is unclean.  Well guess what giraffes and the closely related okapi do both so that’s 7 each of them.  I am also aware that I have been using round figures, and that animals are not cuboid shaped.  If you wanted to put smaller animals under the legs, or above the backs of the larger animals you could do so…though I would ask what happens if the larger creature falls asleep or needs to scratch its rump?

Now a number of leading creationists (most notably Ken Ham) have stated that you don’t need to bring on full sized adults and can thus save space.  You could, but I dispute this with 3 points.

1.  The animals will need to have developed the learned skills for survival from their parents, so they can both survive themselves and teach these skills to the next generation.  This will be even more important in a post-flood world where survival will be even harsher.  This means you’ll need older, more experienced individuals.  You will also need animals to be at an age where they do not require their parents to provide the food.

2.  The idea of bringing the animals onto the ark is so that they can be saved to repopulate the Earth.  For this you will need sexually mature individuals, or those that are about to reach sexual maturity.  Some animals do reach reproductive age early on (brown rat 5 weeks) but others take a long time (African elephants 15-20 years).  So you’re taking young elephants onto the ark…they now need to survive in a devastated world for at least a decade before they’ll produce a new elephant.  Not good if you need them to be popping out babies ASAP.

3.  If the ark is to be floating around for about a year then many of the animals will grow and some will reach sexual maturity during the voyage.  Again brown rats, 5 weeks before baby making, leading to at least 10 generations of rats in a year.  This means that regardless of whether you’re taking juvenile or adult individuals on board, there will be adults by the time you land, so you have to accommodate for adults, PLUS the babies they will be making on board.

So out of the 43,000 cubic metres of space in the ark, the 7 large mammals in the table together have used up over 1000 cubic metres already…and that’s just a few large mammals.  I have been working on lists for other animals, and after a several pages of numbers I got board and gave up.  I’ve done tables for both even and odd toed ungulates and I’ve so far reached 4,088.77 cubic metres used for them, plus the 1040 cubic metres of the larger animals for a 5128.82 cubic metres…basically 1 eighth of the space in the ark…and I’m not done.  This is just some of the mammals currently existing, not to mention the masses of fossil animals known.

One of the common creationist counters is that you don’t need a mating pair from every species currently existing, just a pair from each ‘kind’ and then these can reproduce afterwards to create the present number of species.  The first problem with this is one that Bill Nye presented in his debate with Kem Ham in February 2014; the rapid evolution required to go from the number of species on the ark to the number we have now.  One of the major straw-man arguments used by people who don’t understand evolution is that you “never see a dog giving birth to a non-dog”.  This is a story for another time, but that is what would be required if we are to go from what went on the ark to what is around now; animals giving birth to very different species of animals and 100’s of new animals evolving every year.

So you would take on board a mating pair from the dog ‘kind’, another pair from the cat ‘kind’, a pair from the elephant ‘kind’ etc.  Problem is that ‘kind’ is a very ambiguous term.  A general definition is based upon Genesis 1:24-25 where it describes ‘kinds’ as being able to “bring forth” i.e. reproduce with each other.  This is interesting as a similar definition is used to help scientists characterise species; how easily the organism can reproduce with another individual.  The problem is that in the real world of science there is no line in the sand separating species, but instead a rather fuzzy area.  Let’s take the Cat (Felidae) Family as an example.  At this point I would recommend a video by YouTube user AronRa, it’s part of his Falsifying Phylogeny series and is called Foundations of Feliforme Families as he’ll explain it much better than myself.  We all know what a ‘cat’ looks like, but here are some pictures to illustrate my point (most of the images were taken from Wikipedia)

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All of these are Felids; we have a Cheetah (top left), a Margay (top right), an African Lion (bottom left), a Bengal Tiger (bottom centre), a Eurasian Lynx (bottom right) and my late Domestic Cat called Poppy (centre).  These are all from the Felid Family, but then their lineages really start to diverge.  The Cheetah is from the genus Acinonyx, the Margay is of the genus Leopardus, the Eurasian Lynx if from the genus Lynx and Poppy was of the genus Felis.  All of these are from the Subfamily Felinae.  None of these cats are able to interbreed with each other (or as the Bible would put it, bring forth after their own kind), yet they are still all cats.  As cats evolved the various groups become genetically isolated over time so that breeding first becomes difficult then unlikely and finally impossible.  In the Subfamily Pantherinae, the Lion and the Tiger are an example of this at an earlier stage.  Their respective lineages separated much more recently, they are even still classed part of the same genus (Panthera leo and Panthera tigris respectively).  Breeding lions & tigers is not unheard of (ligers and tigons), but this is difficult and the hybrid offspring is often (though not always infertile).  Eventually the lion & tigers lines will diverge even further to the point where they can no longer interbreed at all in the same way that they currently can’t with a Cheetah, Margay, Lynx or Domestic Cat.

So why do I bring this up?  Well it means that you can’t just get away with saying Noah only needed to bring one pair of cats on board and from their you’ll get all the variety we see today.  If this was so they should still be able to interbreed with each other to produce fertile offspring.  As it happens they can’t.  This means you’ll need many more ‘kinds’ than is talked about.  And for an extra nail in the coffin of creationist ‘kinds’ in Leviticus 11:21-23 there is made distinctions between different types of “locust after his kind”…in fact at least three different ‘kinds’ of locust.  This would mean that the still rather ambiguous Biblical definition of the unscientific word ‘kind’ is much more like the scientific Species and Genus rather than the Family or Order as some creationists would suggest.

Currently our known species count is around;

  • 1,000,000 insects
  • 100,000 arachnids
  • 47,000  crustaceans
  • 85,000 molluscs
  • 17,000 ringed worms
  • 25,000 nematode worms
  • 16,000 centipedes & millipedes
  • 20,000 flat worms
  • 6,000 sponges
  • around 43,300 other invertabrates
  • 300,000 plants
  • 100,000 fungi
  • 5,500 mammals
  • 9,990 birds
  • 8,700 reptiles
  • 6,500 amphibians
  •  31,000 fishes
  • 25,000 algae
  • 29,000 other protists
  • 10,000 bacteria & archaea

Now not all of these creatures will need to go on the ark.  Let’s forget for the minute that there is a difference between fresh & salt water, and that this means that the various fishes, crustaceans, corals, sponges, whales and all other creatures that live there entire lives in the water will not need a space.  This still means that space must be found for several thousand birds, mammals, reptiles, amphibians, worms and arachnids, plus several hundred thousand insects, the seeds & spores of four hundred thousand plants and fungi, plus all the food and water for each animal AND their offspring for the time spent on the ark (about a year) and the time spent out of the ark whilst the landscape recovered before grass etc. can grow back.  And this is just for the animals that are alive today, to say nothing of extinct animals.

This brings me to my next point.  Extinct species.  We know that they can’t have been left out as the Flood story in Genesis tells us that God commanded Noah to take male & female from every kind.  This means that not one kind must be left behind, so that means all of the extinct ones too.  Let’s have a look at the Elephants.  Today there are 3 recognized species of elephant; the African Bush Elephant (Loxodonta africana), the African Forest Elephant (Loxodonta cyclotis) and the Asian Elephant (Elephus maximus).  There are also several recognized subspecies.

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Now you could say “well they’re all of the same kind” and in the case of the two African Elephants that argument might stand, but the Asian Elephant is very much a different species.  Then what about all of the extinct elephants?  Isn’t it just the woolly mammoths and the mastodons? Think again…

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This is just a small sample of the dozens of known genera of extinct elephants.  In clockwise order from top left we have a Stegodon, a Deinotherium, a Dwarf Elephant, a Columbian Mammoth (not quite the same as a Woolly Mammoth), an American Mastodon and a Platybelodon.  Although you could call all of these creatures elephants, many of them lived millions of years apart from each other (Platybelodon being the oldest of the above from about 15mya) and even those living at around the same time where from different geographic areas and looked very different.  So the questions for those that believe in a literal reading of the Flood; which one of them is representative of the elephant ‘kind’?  Which two do you bring with you?  Do you bring all of them?  If only two came along, how did they evolve and reproduce so quickly into the wide variety of elephants that have interactive with humans, to then become extinct so quickly…especially when you consider how long it takes for a baby elephant to reach sexual maturity?  And why don’t we see such rapid evolution of modern elephants?  This starts to lead us to one obvious conclusion.

This brings us to other extinct animals.  When prehistoric life is mentioned people tend to only think of the Dinosaurs, and possibly a few ‘Ice Age’ creatures like mammoths and sabre-toothed cats…but there’s a whole host of other fossils creatures.  Besides around 1000 species of Dinosaur, there are numerous non-Dinosaur creatures that lived at the same time – such as Pterosaurs and Ichthyosaurs (which most people think of as Dinosaurs but aren’t) plus the mass of extinct animals that lived both before and after the Dinosaurs.  Take a look at some of the creatures below.

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I’ve taken visuals from the BBC’s Walking with Beasts series as they give a better image of the creatures than a skeleton will.  At the top left we have an Entelodont and a Hyaenodon battling it out, top right there is a Chalicotherium, bottom right are Macrauchenia and the bottom left Doedicurus.  Although the Entelodont is closely related to pigs and the Doedicurus is closely related to armadillos, they are not ancestors of the modern forms.  As for the others they have no living relatives, in fact they don’t even have anything that comes close.  And these are just a couple of examples; a quick internet search will show you exactly how many extinct relatives these five creatures have, to say nothing of the multitude of other extinct creatures.

I know this has been a rather lengthy post and anybody who has managed to read the 3000+ words so far deserves a round of applause.  The reason it is so long has been to emphasise a point; that Noah’s Ark could not have happened, at least not in the way described in the Bible.  Regardless of what people my say in the story’s defence; the Ark was not big enough to include all of the animals in the numbers specified, regardless of what ‘kinds’ may mean.  That’s about all from me today.  I shall return with more information on how to debunk the Flood Myth at another time.  Always keep learning 🙂

References: Wikipedia (I know not always the most reliable source, but it was good for pictures and measurements, plus a it’s a quick way to get general information on the animals mentioned).  The BBC’s Walking with Beasts.  Aronra’s YouTube video’s Foundational Falsehoods of Creationism (a series), and Foundations of Feliforme Families.  The Bible (King James Version).  Bill Nye vs. Ken Ham debate (you can see this on YouTube).  Answers in Genesis website.

Rock Box – The Rock Cycle

Welcome to my new series of posts called Rock Box.  I will work on these as and when the mood takes me, but my aims are thus; 1) when work commitments prevent me from adventuring out and about, it gives me a chance to do some ‘arm-chair geology’; 2) over the years like many a geogeek I have gathered up a small collection of rock samples…and they could do with organising, so this gives me an excuse; 3) it allows me to explain some basic geological principles to the masses.  So let’s dive in to my rock box. My first post will be a basic introduction to the rock cycle and the major rock groups.  This is to provide a foundation for the rest of the Rock Box series.

The Rock Cycle

Rock Cycle 1a The above diagram is a simplified look at the rock cycle.  The rock cycle starts with magma – molten rock.  As it cools it solidifies into one of the many types of igneous rocks.  From this it can either be eroded away into sediment, or re-heated to form a metamorphic rock.  The sediment will eventually be deposited to form a sedimentary rock and this in turn can either be eroded again into sediment or put under intense heat & pressure to form a metamorphic rock.  And as you’ll have probably guessed by now, the metamorphic rock will either be eroded into sediment or melted into magma.

Igneous Rocks

Igneous rocks are usually put in to two categories; plutonic and volcanic.  In the case of the first, the molten rock moves towards the surface, through pre-existing rock layers, but cools & solidifies before it actually reaches the surface.  Under these circumstances the magma usually cools slowly allowing large crystals to form from minerals with a higher melting temperature.  As the temperature reduces, minerals with a lower melting point start to solidify around the larger crystals.  Examples include granite, gabbro and diorite.

Volcanic rocks occur where the magma has reached the surface (now referred to as lava) and then cooled.  Contact with the air or water usually means that these rocks solidify very rapidly, this causes the crystals to be smaller as they don’t have time to grow.  In the case of more explosive volcanic eruptions the rock can contain air bubbles (both from the dissolved gases in the magma, and from the air it enters whilst cooling). Basalt, rhyolite, pumice and andesite are examples of volcanic rocks. Igneous rocks where the crystals are large & easily visible are referred to as having a phaneritic texture.  Rocks where the crystal are small have a aphanitic texture.

To complicate things even further igneous rocks are also divided by their mineral composition into felsic, intermediate, mafic and ultramafic. Igneous types chart 1aSome examples of good places in the UK to look at igneous rocks;

  • The Uriconian Hills of Shropshire (yeah I’m a Shropshire lad so you can guess why this is top of the list)
  • The Snowdon (Yr Wyddfa) range in Wales
  • Cairngorm & Nevis Ranges in Scotland
  • Central Lake District
  • The Granite domes of Cornwall – Dartmoor, Bodmin Moor & Lands End
  • The Isle of Skye (highly recommend)
  • The Giants Causeway, N. Ireland

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Hay Tor – Granite (Dartmoor, Devon, UK)

Common characteristics of Igneous Rocks are;

  • Solid & hard rock
  • Dense crystal structure
  • Non-porous
  • Often associated with hills & mountains as they tend to be more resistant to erosion
  • Often contain heavy metals & precious stones

Sedimentary Rocks

Sedimentary rocks are formed by the layered deposition of material, often sourced from other rocks.  Sedimentary rocks can be put into several broad categories;

  • Detrital/Siliciclastic
  • Organic Sedimentary
  • Inorganic Chemical
  • Volcaniclastic sediments

Detrital or Clastic rocks are made up of the eroded remains of other rocks cemented together.  Those rocks made up of larger grains (in this case pebbles) cemented together are called conglomerates and breccias.  As the gains get smaller you come to the sandstones, which sometimes contain small pebbles, but are dominated by sand-sized grains.  Finally you reach the mudstones. siltstones and shales which are made up of very small grains (<0.063mm).  These rocks are typically the result of a watery depositional environment such as a river, lake or shallow sea.  This is however not always the case, and other environments such as hot deserts also leave clastic remains.  An example would be the red sandstones from the Permian & Triassic Periods that are common across Europe.  The orange/red colour coming from a layer of hematite that coats the grains.

Organic sedimentary rocks are a mixed group, but all have an organic origin.  One type is limestone which is made up of calcite.  There are a few varieties of limestone from the oolitic with its calcium covered spherical grains to the fossiliferous with its mass of broken fossils.  There are also lime-rich muds and chalk which is made up of the calcium rich remains of microbes called coccolithophores.  As well as the limestones there are the organic ‘rocks’ we commonly refer to as fossil fuels; coal, oil and mineral gas.  OK oil and gas aren’t technically a solid rock, but they have the organic origin and are made from the remains of marine organisms.  These are characterised by the high content of hydrocarbons…something we have found very useful in the 20th century.

Inorganic chemical sedimentary rocks are those that are the result of an inorganic process that deposits the rock layer.  One of the most common of these are the evaporites, rocks that form when water containing dissolved salts evaporates, leaving the salts behind.  Common evaporites are halite, gypsum and anhydrite. Last of all is a cross over of igneous and sedimentary rock.

The volcaniclastic sediments are mainly the result of layers of ash (called tuff), along with pyroclastic flows and occasionally volcanic mud flows called lahars.

Some examples of good places in the UK to look at sedimentary rocks…well most places really, they are really common on the surface;

  • For limestone the Wenlock Edge in Shropshire and the cliffs of Lyme Regis have a lot of fossil rich material, the Yorkshire Dales with their limestone pavements and the North & South Downs plus the White Cliffs of Dover with their chalk.
  • Coal can be found in several layers in amongst the Carboniferous rocks of the Midlands, Pennines and up towards Leeds, along with the Glasgow area.
  • Permo-Triassic rock, including evaporites forms the foundation of much of Cheshire.
  • The Padarn Tuff Formation near Bangor in Wales will be the place to go for volcaniclastic rocks.

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Bedding planes – Comley Sandstone (Ercall Quarry, Shropshire, UK)

Common characteristics of Sedimentary Rocks are;

  • Wide variety of grain sizes depending upon the depositional environment.
  • Often porous and form the source of aquifers and hydrocarbon stores.
  • Contain fossils, and in some cases are almost entirely made up of fossils.

Metamorphic Rocks

The last type of rock is metamorphic rock.  Metamorphic rocks are formed when heat and/or pressure is applied to a rock.  In the earth’s crust & upper mantle the temperature increases at an average rate of 20-30*C per kilometre of depth.  A temperature of about 200*C is needed to start metamorphose of rock and is usually reached about 10km depth.  Pressure is applied to rocks in two different formats.  Lithostatic or confining pressure pushes on the rock from all sides, compressing it fairly evenly.  This usually takes place as a result of deep burial.  In this case the becomes compressed into a smaller, denser form, but maintains the same basic shape.  Directed pressure results when force is applied from a principle plane of direction.  This commonly occurs at tectonic plate boundaries, fold mountains and faults.  This typically deforms on the plane on which the highest pressure is applied.

Rocks that have been metamorphisied are denser than their parent rock.  This is because the pressure pushes the grains together, closing the pores between them.  In directed pressure the grains usually line up perpendicular to the principle direction of pressure.  This prefered alignment is known as foliation.  This often results in metamorphic rocks having a coloured banded pattern.  The increased pressure also has another side effect.  The pressure releases fluids (such as water) from the rock.  This helps facilitate chemical reactions, often resulting in the metamorphic rock having a different chemical composition to its parent rock.

There are several different types of metamorphism, with contact & regional being the most common types.

Contact Metamorphism: This is when a the metamorphism takes place as a result of contact with a heat source.  This is common when you have a magma intrusion.  The metamorphism decreases with increased distance form the heat source.  This type is usually very local.  A good place to see this is around the granite outcrops in Devon.

Regional Metamorphism: This is when the metamorphism is over a large region.  This has two sub-types; burial and dynamothermal.  Burial metamorphism takes place when rocks are overlain by 10km or more of rock.  Dynamothermal metamorphism occurs during mountain building when the rocks are deformed and heated, with some of them being pushed upwards to form the mountains and some of it being pushed downwards to form the mountain base, where heat & pressure work on the rock.  One of the best places in the world to see regional metamorphism this is in Canada where the Canadian Shield covers about half of the country and used to be at the base of a mountain range.

Hydrothermal Metamorphism: This is when a chemical alteration of the parent rock occurs when it comes into contact with hot water.  This is common in volcanic areas with hydrothermal vents.

Fault-zone Metamorphism: Rocks on either side of the fault generate direct pressure on each other, along with frictional heat.

Shock Metamorphism: This occurs where a meteorite hits the ground and the intense heat & pressure causes the metamorphosis.

Pyrometamorphism: Probably the coolest sounding type (yeah I know, not a very scientific thing to say) and is the result of high temperatures but without the pressure.  This can happen in such occurrences as lightning strikes and natural underground coal fires.

Good places to see metamorphic rocks in the UK are;

  • Contact metamorphic zones around the granite outcrops in Devon & Cornwall
  • The slate mine & hills of northern Wales
  • By far the best place, and one that I would recommend if you ever get the chance is the north-west Highlands of Scotland.

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Lewisian Gneiss Formation – gneiss with granite and dolerite (Laxford Bridge, North-west Highlands, Scotland, UK).

Common characteristics of metamorphic rocks;

  • Dense, hard and heavy.
  • Non-porous.
  • Multiple coloured banding.
  • Traces of parent rock.

Final Thoughts

I hope this has been of use/interest to people and not just me whittering on.  I plan on using it as a foundation of other geologically related items, especially as I go through the laborious task of organising my rock collection.  This is a very brief introduction to the rock cycle and the various rock groups.  If you want to know more I suggest finding a good geology textbook.

 References: Fundamentals of the Physical Environment (3rd Edition) by P. Smithson, K. Addison & K. Atkinson (2002).  Geology (2nd Edition)by S. Chernicoff (1999).  Geology of Shropshire (2nd Edition) by P. Toghill (2006).  The Geology of Britain – An Introduction by P. Toghill (2006).  Fossil Revolution – the finds that changed our view of the past by D. Palmer (2003).  Sedimentary Petrology (3rd Edition) by Maurice E. Tucker (2001).

Geological Time Part 2 – The Periods in Shropshire

As part of my geological time series I thought I’d have a look at where rocks/features of the periods can be found in Shropshire.  Shropshire is a very geologically diverse county and if you look hard enough you can find examples from all of the time periods except for the Cretaceous (though the Tertiary is a little dodgy) .  I will say that the examples I am giving are not the only ones to be found in the county.  There are many other formations, rock types and sites that can be used to represent the time periods, I’ve just pick a selected few.  So prepare for a few explanations and quite a lot of pictures.  Just as a remind ma stands for millions of years ago.

Shropshire’s Geological Timeline

Shropshire Geology Time 2

Shropshire Base Map 1

 

I’ve included a brief timeline and a small map giving the rough location of the sites I visited (blue circles) with the major towns in the county for reference.

Quaternary Period (2ma to present)

As we are still living in the Quaternary then many landforms can be seen to represent what has and is still going on in the county.  For a more pre-historical landform a good example would be the glacial relics, of which the kettle holes and peat bogs around Ellesmere would be a good place to start.

DSCF2941DSCF3579These features were formed after the ice of the Devensian Glaciation retreated around 11,000 years, leaving layers of sand and gravel (commonly called glacial till).  The kettle hole forms when a block of ice falls of the retreating glacier and melts, leaving a water-filled depression.

Neogene, Paleogene and Cretaceous Periods

Sadly these formations are missing from Shropshire.  There is rumour of a Tertiary (possibly Neogene) outcrop near Whitchurch, but I haven’t been able to confirm it and I can’t find it on a map, so for now it’ll have to remain a mystery.

Jurassic (200 to 145ma)

You’ll be lucky to find this one.  There is only one real outcrop of Jurassic age rock in the county and that is around the village of Prees, about 5 miles south of Whitchurch.  There is some Jurassic bedrock under the layers of glacial till, but Prees is the only place it comes to the surface.  You can see one exposure, just east of the A49.  To get to it you can follow a public footpath.  The rock is mudstone from 183-190ma and the environment was once a shallow, tropical sea.

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Triassic (252 to 200ma)

The Triassic and Permian are both present in Shropshire, but the exact boundary has caused a little confusion in the past.  This is largely down to the similarities in the formations and the fact that they rest one on top of the other in the same locations.  Personally I think the best place in the county to see both Triassic and Permian is around Bridgnorth, though there are some other impressive red-rock formations that form several ridges in the north of the county.  The Triassic rocks are to the east of Bridgnorth, further up the hill and form part of the Kidderminster Formation.  It is mostly made up of red sandstone and conglomerate.  The image below is that of an exposure on the A442 near Allscott, just north of Bridgnorth and shows a layer of conglomerate sandwiched between two layers of sandstone.  It is a good example of cross-bedding between the strata and is representative of a river running through a desert environment.

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Permian (299 to 252ma)

As I said in the Triassic section, Bridgnorth is the place to see Permian rocks, in fact most of the town is built on it and some of the older buildings are made from it.  The Permian sandstone is also red, shows cross-bedding as the result of wind-blown desert sand, but seems to be a little tougher.  My Triassic samples half crumbled as I was extracting and transporting them.  Again the ancient environment was a desert.

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Carboniferous (359 to 299ma)

For the Carboniferous Period I’ve chosen something a little special; the Tar Tunnel.  Unlike my other choices this is something of a minor tourist attraction and as such will require the parting of a couple of coins.  It’s found in the east end of the Ironbridge Gorge.  The rock in the surrounding area is a mixture of limestones, coals, sandstones, mudstones, and conglomerates from the late Carboniferous Period.  When the Industrial Revolution was in full swing in Ironbridge a tunnel was built to act as short cut between the mines and the River Severn.  Upon digging the tunnel the walls started to ooze natural bitumen.  This was then extracted for a number of years before the industry moved on.  Is there likely to be an oil rush in Shropshire?  Not likely but it is an interesting phenomenon and one that I don’t think can be seen anywhere else in the UK.  If like me you are a ‘geo-geek’ it’s worth seeing.

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If it was red you’d think you were in a cheap horror movie.  The image below shows an pool of tar in a side chamber.

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For a more mundane sample from further up the gorge (Jigger’s Bank) you can see an exposure of the Lydebrook Sandstone.  This layer is made up of a pebbly sandstone and includes layers of conglomerate, and was what I used in the geological timeline above.

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Devonian (416 to 359ma)

Devonian rock actually forms the bulk of Shropshire’s tallest hill; Brown Clee Hill (not to be confused with the neighbouring Clee Hill or Titterstone Clee Hill).

Below is an image of Brown Clee Hill taken from the Wenlock Edge.

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Silurian (443 to 416ma)

The Silurian is very well represented in Shropshire.  One of the best formations in the county (and possibly the country) to see rocks of Silurian age is the beautiful Wenlock Edge.

The Edge is an escarpment that runs for almost 20 miles in a north-east to south-west direction and is made up of of a knoll-reef limestone with lime-rich mudstones & shales surrounding it.

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There are numerous walks along the Edge and due to the old (and current) quarrying activities there are plenty of places to see the local geology.  The above picture showing some wonderfully defined bedding planes.  It is also a good place to go fossil hunting.  There are several places both on and under the Edge were you can collect some nice samples like the one shown below.

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Ordovician (488ma to 443ma)

Like the Silurian the Ordovician Period is well represented in Shropshire, but I’m going to go for a well known formation; the Stiperstones Hills.  The Stiperstones are made up of quartzite and like the Wrekin Quartzite is a misnomer as it is a hard, white sandstone and not a metamorphic rock (like true quartzite is).  The Stiperstones have the added advantage that besides the Ordovician rock, you also have the tors formed from millennia of ice/frost shattering.

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Cambrian (542ma to 488ma)

The Cambrian witnessed a massive diversification of animal lifeforms (often called the Cambrian Explosion) and there some good locations and rocks to be seen in Shropshire.  The Ercall quarry has some wonderful quartzite to sandstone formations, showing beach ripples, conglomerates and inclined strata (see my Ercall post for more)

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The Wrekin Quartzite gives way to the Comley Sandstone.  The type site is the sadly neglected Comley Quarry (located on the north-east slope of Caer Caradoc) where Shropshire’s first Cambrian trilobites were found.  Unfortunately the rock faces are now overgrown and difficult to see.  It can be seen in better condition a the Ercall.

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Precambrian (4600ma to 542ma)

Being such a long eon the Precambrian goes from the formation of the earth to around 542ma.  The Precambrian rocks in Shropshire are mostly from towards the younger end; around 570ma with the gneiss and schist of Primrose Hill possibly being older.  My choice for the Precambrian is the Uriconian Volcanic formation which makes up a number of hills, including the Wrekin, Caer Caradoc and the Lawley.

This photo was taken from the Long Mynd (itself a sedimentary formation from the Precambrian) showing Caer Caradoc (centre right), the Lawley (centre left, and a bit in the distance) and on the left horizon is the Wrekin.  These hills are made up mostly of rhyolite, andesite and basalt.

Below is a sample of basalt from the Wrekin.

IMG_1862Well there you have, a brief geological tour of Shropshire.  The county has seen volcanoes and beaches, deserts and tropical seas and now the efforts of an enthusiastic geo-geek.  Hope you enjoy.

 

Geological Time Part 1- Concepts of Geological Time

In some of my posts I have made mention of certain geological time periods, such as Precambrian, so I thought I’d write a few posts about geological time.  I’m only going to do a brief overview as there are many other sources in which you can get more information.  Most geological text books will cover the subject and even the wikipedia article is worth a look for a little more info.  Oh and in case you were wondering the featured imaged is of the Isle of Hoy, part of the Orkney Islands.  I took the photo several years ago and if you look carefully you can see the geological strata in there.  The cliff itself is about 300m high.

4004 BC, Catastrophism & Uniformitarianism

For most of the past 2000 years the western world has been dominated by Christian theology and this extended to concepts in science.  Genesis was taken literally by many people for the early history of the world, including those who wanted to understand it.  One of the most famous calculations about the age of the earth came from James Ussher, Archbishop of Armagh (lived 1581-1656).  He used the genealogies in the Old Testament to calculate that the world began the night before Sunday 23rd October 4,004 BC.  This calculation became popular (and in some circles this figure is still considered to be the ages of the earth).  Not long after Bishop Ussher scientists – most notably Isaac Newton and Comte de Buffon – started to make their own calculations based on experimentations.  One such experiment was to heat up iron balls and measure how long it takes for them to cool down.  By using such experiments De Buffon eventually calculated that the world was about 74,832 years old.  The venerable physicist Lord Kelvin even weighed in on the issue and using similar ideas thermal diffusion estimated the age of the earth at 20 millions years.  All of these estimates are considerable older than the biblical chronology would have it, but considerably younger than the 4.6 billion years of the current estimate for the earth’s age.

As part of the bible-influenced ideas, one that prevailed was that the geology & geomorphology of the world was shaped by short-lived, dramatic events, in particular Noah’s Flood.  These events were used to explain such things as why their were fossil shells in mountainous areas and why the deep, wide valleys of northern Europe contained rivers that seemed too small to carve them out.  This idea is known as catastrophism.

It didn’t take to long for early geologists working in the field to realise that ideas of catastrophism weren’t seen in the rocks they studied.  What was seen was evidence of processes going on today; rivers depositing sediment, glaciers carving out valleys, sand dues creating angular layers etc.  One of the first geologists to recognise this was James Hutton and he developed the concept of uniformitarianism.  This idea is basically that the laws of nature and the processes that go on now are the same as those that went on in the past.  Catastrophes were not needed to explain the earth’s geology, and in most cases the slow but continuous processes like uplift, erosion and deposition explain what is seen much better.

In modern geology uniformitarianism is seen as being basically true in the ‘day-to-day’ processes, but there is the recognition that dramatic events do happen.  Meteorites impact the earth, large volcanic eruptions and flood basalts do take place and such events can have a dramatic impact on the local (and very occasionally global) geology.

Geological Time Scale

As the study of geology developed several distinct time periods started to be noticed.  Along with uniformitarianism a very simple principle was recognised; the law of superposition.  This is a simple concept; sedimentary layers are deposited in a time sequence with the older layers being at the bottom and the younger layers at the top.  Uplift, folding & faulting can disrupt this sequence, but such processes are usually evident.  Fossils were used to help define such layers and a sequence began to emerge with simpler organisms at the bottom and more complex ones higher up the sequence (yes this is a bit of a generalisation I know).  The presence of the same fossils in different rocks around the world is usually an indication that the rocks are the same age.

Below is a simple diagram of the geological time scale as we currently understand it.

Geological Time 1

The earth is currently estimated to be around 4.6 billion years old.  The above diagram shows the Eons that earth’s history is divided into.  It is roughly to scale.  The Proterozoic, Archaean and Hadean Eons are collectively known as the Precambrian and represents the early earth.  Rocks from the Precambrian form the base of the continents and are often metamorphic in nature.  To give you an idea of scale the most famous extinct organisms, the dinosaurs, lived in the highlighted section of the Phanerozoic (green box).  Being more recent the rocks of the Phanerozoic Eon are more prolific, easier to define and better preserved.  Starting from about 542ma the Phanerozoic is divided as below.  The dates to the side are approximations as there is a margin of error of a couple of ma either side, with some sources quoting slightly different dates.

Geological Time 2

Again this table is roughly to scale.  Click on the image and you should get a better resolution.  The Palaeozoic (formally know as Primary) has early life and sees the evolution of arthropods & fish in the earlier periods, amphibians, reptiles & proto-mammals in the later periods.  The Mesozoic (formally Secondary) is the age of dinosaurs and tends to be the era most people think of when you mention prehistoric life.  You also had further development of mammals and later birds, along with flowering plants.  The Cainozoic is often called the age of mammals with the Neogene and Palaeogene often being called the Tertiary.  The current time period is the Quaternary and is usually defined as being the last 2 million years up to the present, and contains the so called ice ages.

Telling Time Geologically

Until the discovery of radioactivity there was no absolute way of determining how old a rock was, hence the variations in trying to determine the age of the earth.  Early geologists could only date rocks relative to each other; so called relative dating.

Relative Dating: this uses the law of superposition and uniformitarianism to date the rocks relative to each other.  Unless the layers have been disturbed through processes such as faulting, folding or intrusions, the older layers of rock will be at the bottom and the younger ones at the top.  You can then compare the fossils in each layer to see for differences.  Extinction and evolution will lead to some creatures disappearing and being replaced by other organisms in a sequence up through the rock layers.  This can then be compared to rocks from elsewhere and if you find the same fossils then the rocks will be of a similar age.  This then allows you to compare the fossils & layers in the new site for differences there and so.  This allows you to compare & contrast layers to each other so that you know how old a rock layer is in relation to others around it.  You can then compare current rates of erosion and deposition to then make estimates of how long it took to for the geographic process (say a river depositing a layer of silt) to form a layer of rock that think.  Thus giving you an idea of how old the rock may be.  Even in areas where the rock has been deformed you can study how the layers have changed and get a good idea of how old they are in relation to each other.

Absolute Dating: after the discovery of radioactivity and radioactive decay it was realised that you could get a more accurate date for rocks.  The most common method used is radiometric dating.  I’m only going to do a brief intro to this as to give it a full description would take pages.  The most well known type of radiometric dating is radiocarbon dating.  This uses the radioactive carbon-14 to determine a date.  It can only be used for objects containing carbon (e.g. living material) and only for objects up to about 70,000 years old.  Other radioactive isotopes can be used to for older materials (such as Uranium-Lead, Potassium-Argon and Rubidium-Strontium).  Regardless of the isotopes used the method is the same.  As the atoms decay they lose electrons, protons & neutrons and the original atom (parent atom) becomes a different atom (daughter atom).  This radioactive decay is a constant (there are a few special circumstances such a nuclear fusion that resets this clock).  By determining how long it takes for half of the parent atoms to decay to the daughter atoms you can then measure the ratio between the parent & daughter atoms in a sample of rock.  This will then give you a good estimation for the age of the rock.  This can only be done to igneous rocks as when the molten rock solidifies the crystals that contain the radioactive material are fixed in the rock until you take the sample.  With sedimentary rocks the original material has been eroded away, the crystals are no longer complete and so you cannot get a good ratio reading.  Even if you did get an accurate reading you’d be getting a reading for the crystal not the sedimentary rock it sits in.  For metamorphic rock the crystals have been deformed or broken up by heat & pressure again preventing you from getting an accurate reading.s7001758.jpg

(Metamorphic Lewisian Gneiss, with granite mixed in from north-west Scotland)

There are other absolute dating methods that can be used; dendrochronology, fission-tracking, sediment layers (e.g. in mud), annual snow fall/melt layers in ice to name but a few.  By combining absolute and relative dating methods geologist can determine the age of the earth and the various rock layers that make up its surface.

If you wish to know more about geological dating methods I’d suggest you find a decent geological text book, that’ll describe these methods in greater detail.  For the purposes of my blog writing this brief introduction should suffice.  For part 2 I have been working on something a little special and it has taken a bit of time to gather the necessary materials.

References: Fundamentals of the Physical Environment (3rd Edition) by P. Smithson, K. Addison & K. Atkinson (2002).  Geology (2nd Edition)by S. Chernicoff (1999).  Geology of Shropshire (2nd Edition) by P. Toghill (2006).  The Geology of Britain – An Introduction by P. Toghill (2006).  Fossil Revolution – the finds that changed our view of the past by D. Palmer (2003).