Icelandic earthquake M6.2 11 km northwest of Selfoss at 15:46:01 UTC
Earthquake recording at Keele University, Midlands, UK
Iceland Earthquake M6.2 Near Selfoss
Earthquakes
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May 292008
Accretionary Wedge #9: Deep Impact
accretionary wedge, geology
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May 212008
The topic for the latest accretionary wedge hosted at Harmonic Tremors is a significant geological event.
Source: Robin M. Canup, “Simulation of a Late Lunar-Forming Impact,” Icarus, vol. 168 (2004)
Julian at Harmonic Tremors has left the term ‘significant’ open to interpretation so here is mine. I think that the most significant event in Earth history was the impact of a Mars sized body about 4.53 Ga on planet Earth which lead to the formation of the Moon. Our Moon is much larger than moons of other terrestrial planets and has had a very significant affect.
This was significant in so many ways. To start on a ‘small scale’ the Moon’s gravitational attraction generates tides and has effects on ocean currents, global climate and life in the tidal zone.
The Moon has had a stabilising effect on the Earth’s rotation axis. Earth’s rotation has enough of a wobble to affect climate (via Milankovitch cycles) but Mars has had much more of a wobble resulting in large variation in ice caps across the surface. It can be argued that Earth’s (relatively) stable climate has promoted evolution of higher life forms.
However, I think that there are other important effects as a consequence of the Earth absorbing the impactor’s core, giving the Earth a larger than normal core. First there is the generation of a large magnetic field compared to other terrestrial plants. This has protected the Earth’s surface from harmful radiation which could have been seriously damaging to life on Earth. Second is the potential consequences for plate tectonics. There have been recent articles suggesting that if global warming were to increase, plate tectonics would cease a the thermal gradient driving convection would decrease. What is being ignored here is the contribution from below. There is a significant contribution of heat from below as the Earth cools overall and the lower part of the liquid outer core ‘freezes’ to become solid inner core. Without the Earth’s enlarged core we could have ended up like Venus. No convection in the liquid core, no magnetic field, limited mantle convection and possibly no plate tectonics either.
Without either a strong magnetic field or plate tectonics it would be unlikely that life (at least as we know it) would exist on Earth. I’d call that significant.
Another weekend, another geoblogosphere meme. This time Dave at Geology News asks about first field trips.
Like several others that have followed the meme, my first field course was a bit too long ago to have photographic evidence (I don’t remember having a camera with me and if I did I don’t have the photos any more – not that I pre-date photography!). My first field course was to the Isle of Wight, off the south coast of the UK. It was a joint geology / geography field course and I remember it more for putting me off ‘human’ geography for life (I absolutely hated going up to complete strangers and asking them pointless questions on village living – the place was called Godshill – how these things are burned into one’s brain even though it’s getting on for thirty years ago). The geology concentrated on the Isle of Wight monocline, an alpine fold producing near vertical Cretaceous and Palaeogene beds.
The Lost Geologist and Silver Fox have somewhat diverted the meme to first geological equipment.
I still have my first hammer. Being a ‘hard rock’ geologist originally I’ve always considered an Estwing a bit of a ‘toffee hammer’ and preferred my trusty two and a half pound Whitehouse. I just have to remember to soak the shaft in water before I go into the field.
I’ve also still got my somewhat battered first hard hat. The crest on the front is that of the Royal School of Mines where I did my degree. The logo on the brim is that of the Institute of Geological Sciences, the former name of the British Geological Survey. Since my initials are IGS I thought that they wouldn’t mind me taking over their logo as they had changed name to the BGS a couple of years beforehand. The very battered sticker on the side is University College Cardiff Geophysics where I did my Ph.D.
Pangaea, geology stylee
geology
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May 122008
Following the Pangaea Day geoblogosphere meme, started by Chris@goodSchist and followed up by Callan@Nova, Brian@clastic detrius and Chris@highly allochtonous I suppose I should give it a go.
This was harder that I thought. I’m still not sure I’ve got it perfectly correct (I may be a touch too far north) but I think that Britain was under the red dot on this version of Ron Blakey’s palaeogeographic map for the Late Triassic (220Ma).
In the Triassic things are happening fast. The Variscan mountains of the late Carboniferous / Early Permian to the south have all but disappeared and extension related to the opening of the North Atlantic is causing rapid subsidence. The Bakevellia Sea is to the west and the Zechstein Sea to the east in the Permo-Triassic with a possible connection north to the Boreal Ocean. As subsidence occurs, by Late Triassic / Early Jurassic these seas link up and most of Britain becomes shallow marine with a number of small islands just remaining.
The Faroe-Rockall Basin forms to the west forming the start of the North Atlantic rift. If it had come down the failed Viking Graben rift to the east things would have been very different for us.
Magnitude 7.8 Earthquake, Sichuan, China
Earthquakes
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May 122008
The magnitude 7.8 earthquake, Sichuan, China as recorded at Keele University, UK.
