Bristol Earthquake

You have probably all heard about the magnitude 4.1 earthquake that hit the Bristol Channel on Thursday at 1:21pm. It was felt by people in South Wales, Somerset and Devon (unfortunately not as far as Plymouth!), but did not cause any significant damage.

Earthquakes in the UK are more common than you might think - we have around 20-30 each year that are felt by people, and hundreds of smaller ones that are felt by sensitive instruments. The largest British earthquake occurred near the Dogger Bank, 60 miles offshore in the the North Sea, and it had a magnitude of 6.1. As it was so far out to sea, the damage was reduced, but it was still powerful enough to cause minor damage to some east coast buildings. The most damaging British earthquake occurred in Colchester in 1884 with a magnitude of 4.6, damaging 1,200 buildings. The picture below shows a map earthquakes from 1932 to 1970 with a magnitude of 3 and above (yellow) and earthquakes from 19070 to present with a magnitude of 2 and above (red).

UK seismicity (courtesy of the BGS)

The UK experiences a magnitude 2 earthquake roughly once every two years, and a magnitude 5 earthquake roughly once every 10-20 years. Most earthquakes occur on the western side of the British mainland, and are nearly absent from eastern Scotland and north east England. These earthquakes are due to the many faults in Britain. The actual driving forces are unclear, however it is likely that they include regional compression due to the motion of the Earth's plates and uplift due to the melting of ice sheets that used to cover Britain.

Fossils, Fossils, Fossils!

Researchers in Canada have uncovered a new fossil site  near to the Burgess Shale, which is famous for it's preservation of the soft parts of fossils. This new site is revealing fossils at an amazing rate, which will allow our understanding of animals from the Cambrian period (540-485 million years ago) to be significantly increased. So far, 12 new species has been found, but it is likely that new discoveries will continue to be made. The exact location of this new site is being kept confidential, to stop thieves from targeting it.

The amount of fossils in the Burgess Shale and in the new site is due to the Cambrian explosion (540 million years ago), which was the cause of the rapid increase in the abundance and diversity of animals. There are many possible causes of this explosion. The ozone layer (which blocks out the lethal UV radiation) is believed to have formed during the Cambrian explosion, allowing for the development of complex life and life on land. The amount of oxygen in the atmosphere also increased during the Cambrian explosion, allowing larger, complex animals to grow, as they require a larger amount of oxygen to survive. Volcanically active mid ocean ridges during the Cambrian caused an increase in the amount of calcium in the oceans, allowing marine organisms to build hard body parts, such as skeletons, allowing for a greater diversity of complex life. All of this has allowed for more animals to be preserved from the Cambrian period, explaining why so many fossils are found from this time, and why I now want to go to Canada!

Ancient Volcanoes and Fossilised Animals

Pompeii victims (courtesy of the BBC)

Now you all probably recognise the picture above. In 79AD, Mount Vesuvius erupted, wiping out the city of Pompeii, killing and burying its residents under a dense layer of ash. Scientists now believe that similar events may have occurred 130-120 million years ago, instantly killing the animals of the area and preserving them in a similar way. Fossils beds from the Liaoning province in NE China are the site of some exceptionally well preserved feathered dinosaurs, mammals, lizards, birds, fish and insects. They would have lived in an area that was surrounded by volcanoes, and would have been the victims of pyroclastic flows (I'll explain them in a minute) that spread out across the landscape. Like the people of Pompeii, they would have been killed instantly, before being buried under the ash, allowing them to be preserved in mid-movement. The animals were found together as their carcasses would have been transported by the flow and deposited in the same area.

Fossil dinosaur and birds (courtesy of the BBC)

Pyroclastic flows consist of hot, dry rocks and hot gasses that travel away from a volcano after an eruption. The coarse rocks move along the ground, and a turbulent cloud of ash rises above them, which combined can destroy nearly anything. Flows can reach speeds of over 50 miles per hour and temperatures often range from 200-700 degrees centigrade. The rocks batter, destroy or carry away most objects and structures, whilst the temperatures burn things like vegetation and houses. Sites are then buried by the hot rocks and ash. So basically, you do not want to get in the way of one of these things!

Although that's all very doom and gloomy, these ancient eruptions have allowed us to have these exceptionally well preserved fossils, giving palaeontologists a greater understanding of life and evolution from such a long time ago.

Microscopes and Paintbrushes

I've been busy with my samples again in the lab. I put the stubborn sample that hadn't broken down into white spirit to help dissolve it further, before leaving it in boiling water overnight. I then re-sieved it over the sink, re-filtered it and put it back in the 40 degrees centigrade oven overnight. When it is was dry, I sieved it through 1mm, 150 micrometre and 63 micrometre sieves (it still wasn't completely broken down, so there was a lot of large material, hence the larger sieve).

Large material from the stubborn sample!

I then picked through my samples for microfossils for the over 150 micrometre material. This involved putting a thin amount of material on a picking tray, putting it on a microscope, and, using a fine paintbrush, looking at every single grain, and moving the microfossils from the tray to a slide. This was a lot of hard work, as the grains and microfossils were prone to either getting stuck to the paintbrush, or flicked off into the distance!

Desk complete with microscope!

Material on picking tray

Lots of microfossils on slides

I then stuck down the microfossils onto the slides from two of the samples, as there weren't very many in either of them. I then separated the microfossils from the other two samples, specifically picking out foraminifera (forams). I am now in the process of sticking down the forams, and I will then stick down the rest of the microfossils.

Some of you may be wondering what on Earth foarms are! Well, they are marine organisms that first appeared around 540 million years ago, and are still alive today (well, not the ones that were around 540 million years ago!). They are split into two major groups - benthic (species that live on or within the seafloor sediment) and planktic (species that float in the water), and they generally have a shell, with either one or multiple chambers. I am using the forams and other fossils to determine where the samples came from - either from the deep water or near the coast. This will hopefully allow me to determine if they were affected by a tsunami.

Many different forams (courtesy of Wiki)