The oldest bit of the Earth

Many of you will have heard me discuss in class that when I was a student (which isn't that long ago!) I learnt that the oldest rock in the crust was 3,800 Ma from Greenland; this had changed to 4.200 Ma from dating a rock in northern Canada.  We now have to revise that number again as a Zircon crystal from Western Australia has been dated (by the Uranium-Lead method) to be 4,400 Ma.  We still have meteorites that are older, but we are finding fragments of the earliest crust which may give us an indication of the processes that formed our planet.

Lagerstätten

Lagerstätten are sedimentary deposits that show remarkable fossils that otherwise would not be preserved.  It is a German word that literally means "resting place" which, I think, is a very appropriate word for such a special and important piece of the fossil record.

There are quite a few of these around the world which give us tantalising snapshots from the history of life.  Several of these are very important in our understanding of key moments in evolutionary history such as Archaeopteryx (shown above) from the Solnhofn Limestone in Germany and the incredible soft-bodied "experimental life forms" of the Burgess Shale.

Another of these was discovered very recently, a site of a mass beaching of whales in the late Tertiary of Chile.

Did you feel it?

We had an earthquake today!  A magnitude 4.1 tremor with its epicentre in the Bristol Channel, just north of Ilfracombe was recorded by the British Geological Survey at 1.21pm.

No reports of damage yet, not even knick-knacks falling! Have a look at a 'VI' on the Mercalli Intensity scale.

That sinking feeling

We seem to be experiencing a spate of sinkholes suddenly appearing in places around the UK.  They are the result of caves collapsing as the rock that support their roofs is undermined by erosion.  They have appeared several times on the news and there has been an explanation of their formation by a geologist from the BGS.  The rise in groundwater levels caused by the recent heavy rains combined with geological vulnerability of certain rocks (chalk and gypsum are particularly vulnerable) make these hazards sudden and unpredictable.  Security camera footage from the National Corvette Museum in the US shows a hole forming.

The Vale of Glamorgan does suffer from sinkholes as well because our bedrock geology here is mostly limestone.  How solid is the ground under your feet?

Seismic Puzzle

The earthquake hazard map of the USA has a major seismic puzzle.  It's not the high hazard in California (CA) caused by the San Andreas Fault or in Washington (WA) and Alaska (AK) easily explained by the occurrence of subduction zones around the Pacific Ring of Fire.  There is another high hazard zone along the Mississippi River further east.

Harri P in Year 12 drew my attention to this odd occurrence of earthquakes thousands of kilometres from a plate boundary.  There have been some major seismic events in this region, in particular the magnitude 7 New Madrid earthquakes of 1811-12.  The cause of these 'quakes was a puzzle until a few years ago when a team of geologists from the University of Quebec discovered a slab of crust that is descending into the mantle, disrupting the flow of the mantle and the crust in this area.  It is similar in some ways to a subduction zone but without the fold mountains, trench and volcanoes.  It does pose a continuing danger of creating major earthquakes.

It is a very strange phenomenon and goes to show just how much we still have to discover about how the crust and the mantle work.

The beauty of columnar joints

Columnar joints in igneous rocks make some of the most spectacular sites in geology, especially if you travel around Iceland.  Take a look here to see some of the best from around the world.

I also like how these distinctive geological structures can get used.  There are suppliers who can sort you out with columns of different sizes for your garden; they can be used as the plinth for sculptures, benches and bollards in the street, garden tables, memorials and (my own favourite) gravestones.  What would you use them for?

  

Thanks to Rosie for sending the link.

The Paradox of Plenty

It is a hidden secret of our increasing desire for and use of electronic gadgets that many of the minerals essential to their manufacture are both the product of, and the finance for, war.  

Mineral resources are distributed by geological accident rather than geopolitical convenience.  This can create the potential for enormous geological wealth in places that do not have the political and financial stability for their exploitation to benefit the communities in which they are located the 'Resource Curse'.  You may be familiar with the concept of 'Blood Diamonds' from the film, but less well known is how gold, tin, tungsten and coltan can also be produced in situations of conflict and terrorism.

Apple produce an annual report to detail the source of the mineral resources that go into their iPhones, iPads and Macs showing how many of their suppliers meet international standards of human rights and environmental protection.  It makes for interesting reading and it does how the importance of geological exploration to locate the resources we need in a wider variety of places.  Do you think about where the minerals in your gadgets started out as rocks in the ground?