The second edition of this guide is written to explain the key concepts of tectonics and rock structures to students and to interested amateurs. I have reviewed a number of Graham Park’s books in recently years (see below) and he is clearly a prolific and excellent writer of books about the earth sciences.
Tony and Anna Gill (UK) The best time to look for fossils in Dorset is after heavy rain and winter storms. These conditions make the cliffs unstable and collapse. High winds produce rough seas, which wash the mud away, leaving the nodules that contain the fossils exposed on the beach. The beginning of November 2005 saw a period of heavy rain and strong winds. This stormy weather continued for several days and on 5 November gale force 10 winds, before a high tide, exposing new material (Fig. 1). Fig. 1. A large landslip, approximately four hundred metres east of Charmouth, contains most of the best fossil horizons. This slip is illustrated with the sea crashing into it (Fig. 2). The large stones in the picture below do not contain any fossils. If they did, they would not be there. The best place to look for smaller fossils is around these large stones. Some of the pyrite ammonites found here can be up to 25cm to 30cm in diameter. Fig. 2. The storm crashing against the cliffs at Charmouth. The flat stones, which are from the Obtusum Shales, sometimes contain the ammonite Asteroceras Planicosta and usually the smaller ammonites Promicroceras Planicosta (Fig. 3). Fig. 3. Charmouth was the seabed in Jurassic times, some 195 million years ago. The football shaped and sized, Stellare Nodules, when broken, contain calcite crystals. Occasionally though, an ammonite can be found inside the larger ones. These ammonites can be up to 50cm across, but unfortunately, most … Read More
Dr Richard J Hubbard (UK) Introduction The Thanet Anticline is an uplifted area forming the northeast corner of Kent and is home to the four coastal towns of Birchington, Margate, Broadstairs and Ramsgate (Fig. 1). Historically, the area has been known as the Isle of Thanet and, in this article, I will look at sediment deposition and erosion around the upstanding anticlinal structure and how shorelines have shifted during the past two thousand years. I will finish with some thoughts about how shorelines might look one hundred years from now. The article is based on material drawn from three guidebooks published by GeoConservation Kent, written by Geoff Downer and myself (see below). Fig. 1. The Isle of Thanet. Sketch map of northeast Kent to show the geography of the Wantsum Channel at the time of the Roman occupation. Today’s shoreline is superimposed with some medieval settlements added for orientation. The Isle of Thanet is elevated and forms an ‘island’ because of the underlying structural geology. Note the location of the offshore seismic line published by Ameen (1995), on which the cross section of Fig. 4 is based. (Figure 87 from The Smugglers Trail, Hubbard & Downer, 2021.) This article has also been written to accompany a book review that was recently published by Deposits (see Book review: The Smugglers Trail – Geology of the Thanet Coastline from Broadstairs to Cliftonville, by Richard Hubbard and Geoff Downer). Thanet has been a high standing area for more than 300 million years and … Read More
Helen Gould (UK) Chemistry is the key to identifying the source of a meteorite. The commonest rock in the Solar System – and on Earth – is basalt. Erupted at mid-ocean ridges and many hotspot volcanoes, it also floors the oceans. However, each of these situations can be identified as geochemically different from one another. Some meteorites have geochemical signatures associated with individual asteroids, being either enriched or poor in specific minerals. The ratios of their minerals are plotted against one another, then the shape and co-ordinates of the plots are cross-referenced to a database. This process has allowed distinct groups of meteorites with similar geochemistry to be identified, suggesting that the meteorites in each cluster plotted came from the same source. There are five sub-groups of achondrites of various chemical composition, including eucrites, diogenites, SNC, lunar achondrites and ureilites. The name means they don’t contain chondrules. Most are of igneous origin, but lunar achondrites resemble fragmental sedimentary rocks. The only “weathering” on the Moon comes from impacting meteorites, but this breaks up rocks and reforms them into breccias – jumbles of jagged fragments fused together. Eucrites Eucrites are basaltic meteorites containing low-calcium proxenite and plagioclase feldspar with metallic iron, troilite (iron sulphide) and silicates. They probably all crystallised at or just below the surface of their source bodies. Fig. x. Eucrite. Diogenites Diogenites consist of calciumpoor pyroxenite, which is an igneous rock resembling the ocean crust. Fig. x.. Diogenite. SNC SNC meteorites have been identified as coming from Mars. … Read More
The Crowood Press are really developing a nice little series of books on the landscape and geology of select regions of the British Isles, and Tony Waltham’s addition to the series about the Peak District is well worth a read. This new one follows the same format as the others – beautiful, full colour photos and diagrams, a fascinating chapter on each of the important geological and geomorphological aspects of the area (including buildings and industry), and an author who knows his stuff and can write it down with an easy and authoritative style.
Thomas H Rich and Patricia Vickers-Rich (Australia) Whether they had horns or not, the ceratopsian “horn faced” dinosaurs are distinctive, not only from other dinosaurs, but all other vertebrates as well, in the structure of their skulls. In addition to the horns, another element of their skeleton, the lower arm bone (called the ulna or elbow bone), unexpectedly is so distinctive that it has provided clear evidence that, 130 million years ago, these very ceratopsians were living in Australia. Prior to that discovery, the ceratopsians were known almost exclusively in the Northern Hemisphere. Just over a century ago, a toothless lower jaw found in Patagonia, Argentina was named Notoceratops, “the southern horned face”. The last time that fossil was seen was a decade later when the world-renowned dinosaur authority, Fredrich von Huene, studied and redescribed that fossil and agreed unreservedly that it was a ceratopsian. Illustrations of that bone strongly support its correct identification as a ceratopsian. However, unfortunately, von Huene is the last person known to have laid eyes on it, and the fossil cannot now be found. Thus, the only ceratopsian previously thought to have come from the Southern Hemisphere, disappeared. When the Victorian dinosaur ulna, which is the subject of this article, was first found at the base of the Arch near Kilcunda (Fig. 1) by Mike Cleeland, Tom’s first guess was that it was some kind of carnivorous dinosaur or theropod. This was because it was a short, stumpy bone, which is so characteristic of the … Read More
Lutz Andres (Germany) The giant-toothed ‘Megalodon’ shark (Carcharocles megalodon,) is one of the most impressive extinct creatures to have excited our imagination, and its fossilised teeth are one of the most desired objects in the fossil collecting world. Fig. 1. Carcharocles megalodon. A lot of collectors and scientists believe that Megalodon is closely related to the Great White shark (Carcharodon carcharias), because of their similar teeth, which are large, triangular and serrated shape. However, that point of view is too superﬁcial. There are a few clear differences in the tooth morphology. In addition, they had apparently different kinds of nutrition and their dental weaponry suggests different hunting strategies. A few obviously different tooth characteristics between such closely related species will be described and discussed below. Different root shapes The root branches of the upper and lower anterior teeth of all giant-toothed sharks (Otodontidae) are elongated to resemble a ‘V’ or ‘U’. The roots of upper anterior teeth in Great White sharks are often nearly rectangular, without well-developed root branches. When the Great White shark attacks and bites its prey, the lower anterior teeth are the ﬁrst to penetrate the body, and then the shark closes its jaws. After that, it starts immediately to shake its head in a semi-circle shape, to rip ﬂesh out of the body, mainly with its upper anterior teeth. The pressure on these upper anterior teeth is applied laterally. Therefore, the roots have wider surfaces to absorb the laterally arising forces. Fig. 4. 1 and 3 … Read More
Deborah Painter (USA) I am an ecologist and general environmental scientist living in the USA and specialising in transportation, energy and industrial development planning to minimise deleterious environmental impacts. I have also written several articles for this magazine. As such, I appreciate just how much local geology is a vital consideration in many circumstances and especially during one of my routine responsibilities – undertaking a Phase I Hazardous Materials Site Assessment of an industrial or commercial property in the United States. This is the first of three articles on how I and other environmental scientists apply our knowledge of geology in our day to day work. But what is the purpose of these assessments? Companies such as my employer do these to benefit a person or business desiring a loan from a bank to purchase a property or to pay for upgrades. Cities and counties also contract with environmental companies for Phase I Environmental Site Assessments for properties they own and want to improve, or intend to acquire for resale to private parties. For example, city officials may have their eyes on an old former school and grounds as the future site for a new police station, and want to know how expensive it would be to renovate it as opposed to demolishing it to build a new structure. The assessment is done to satisfy the current American Society of Testing and Materials (ASTM) Standard E 1527-13: Standard Practice for Environmental Site Assessments (2013), and the United States Environmental Protection … Read More
By David N Thomas and David G Bowers The extent to which our planet is covered by oceans and seas (about 70%), and the increasing concern that right-minded people have about climate change, means that there is a both a desire and an urgent need to know more about and … Read More
Byron Blessed (UK) 9:30am, Saturday, 15 April 2006. I set off with my fossil- hunting party from my shop “Natural Wonders Ltd” on Grape Lane in Whitby. The weather was overcast but ﬁne, and bright enough for the sun to break through later in the day. As I led the 15-strong party up the famous Whitby Abbey steps and along the Cleveland way to Saltwick Bay, no one could have anticipated this would be the day that I would find the best fossil I have ever collected. Fig. 1. Byron and faithful sidekick investigate the rock further. My fossil-hunting trips are really designed for the complete beginners: those who don’t know what they are doing, who have no idea about the safety issues involved in fossil collecting, and certainly have no idea what type of rocks to look for. Therefore, I had designed this trip to suit these needs, so that people can then go out and “do it themselves”. The great thing about fossil collecting is that you never know what you’re going to ﬁnd when you get onto the beach. So, after a run through of the “golden rules of fossil collecting” (tides are dangerous, cliffs are dangerous, bring the suitable equipment), it was straight into the shingle to search for the nodules containing the best ammonites. Fig. 2. One freshly excavated croc skull. Our return trip to Whitby is always along the foreshore past Saltwick Nab and under the East Cliff (also known as “the Scaur”). It … Read More
This is an ambitious little field guide, which aims to allow amateurs to identify basic rocks and rock formations, for the first time, in a systematic way., as it says: “… using only careful observation, a magnifying glass, a pocket knife – and a bit of patience”.
Stephen Moreton (UK) Our journey around Ireland concludes in Ulster. This comprises Northern Ireland, which is part of the UK, and the counties of Cavan, Donegal and Monaghan, which are part of the Republic of Ireland. As geology is no respecter of politics, the national border is ignored here. I assure my gentle readers that this is not intended as a political statement! The geology consists of metamorphic rocks and granite intrusions in the west, a huge expanse of Tertiary basalt in the eastern half, and a series of Tertiary granite intrusions in the southeast corner. Carboniferous limestone makes an appearance in some places, but is not as well endowed with minerals as further south. Fig. 1. The four regions of the island of Ireland. Fig. 2. Ulster in more detail. Donegal, occupying the northwest corner of the island, has such a varied geology that it has long been a favourite venue for university ﬁeld trips. In spite of this variety, there are few mining sites. Lead has been mined at Glenaboghil, Keeldrum and Glentogher, but these old mines are not noted for specimens. However, minor yellow powdery greenockite occurs at the ﬁrst location and green coatings of pyromorphite at the second. What it lacks in mines, the county makes up for in silicate minerals. The beryl occurrence at Sheshkinnarone is probably the best known. Finger size green and blue-green prisms in a white quartz matrix occur at several spots here. The richest is just outside the garden wall of … Read More
Helen Gould UK) What are meteorites? Lumps of rock left over from the formation of the solar system or “chipped off” planets during major impacts can become trapped in the Earth’s gravitational field and fall as meteorites. The three main types are iron, stony and stony-iron. All of these are discussed in this article. In particular, I consider two important questions: Why are they so important? Because they represent the growth (accretion) of planets, they carry clues to our Solar System’s formation.How do we know we are dealing with a meteorite? Like other rocks, meteorites record events. Most of their minerals are familiar but some have higher or lower concentrations than rocks found on Earth, suggesting an extra-terrestrial origin.Irons Fig. 1. Iron meteorite. Most contain 7-15 wt % of Nickel (Ni) metal, with traces of other minerals. At room temperature, instead of a single mineral, this forms a Widmanstätten structure, whose intergrowth lamellae show two different minerals, one with about 40% Ni, the other with only about 5% Ni, and indicate slow cooling from greater than 700°C. Iron (Fe) meteorites have usually been completely melted, proving they formed in asteroid cores. So even asteroids are differentiated – like the major planets – with a core and mantle which solidified slowly. Widmanstätten patternsAlso known as Thomson structures, these are figures of long nickel–iron crystals, found in the octahedrite iron meteorites and some pallasites. They consist of a fine interleaving of kamacite and taenite bands or ribbons called lamellae.Stony-irons Stony-iron meteorites probably … Read More
I like local geological guides, which aim to get you out and about, visiting areas you might not have known are worth a daytrip. And this is a good example. I sat down and read it cover to cover, as it is only 90 pages long. And I now really want to visit this bit of Kent coastline. Largely concentrating on the Upper Cretaceous Chalk, this guidebook explains and illustrates what seems to be some marvellous geology that can also be explored during what could be a lovely day out on the beach.
Stephen Moreton (UK) In the ﬁrst two articles of this series, we looked at Leinster and Munster. Continuing in a clockwise fashion brings us to Connaught. Some of Ireland’s oldest rocks are to be found here, forming the Ox Mountains. The rugged and mountainous west is dominated by metamorphic rocks and a series of granite intrusions. Inland, Carboniferous limestone prevails. Fig. 1. The four regions of the island of Ireland. Fig. 2. Connaught in more detail. Where the latter abuts Devonian sediments is found the jewel in the crown of Irish mineralogy – Tynagh Mine. This giant polymetallic deposit, near Loughrea in County Galway, was discovered in the 1960s and yielded close to a million tonnes of lead, zinc and copper. Much of this was as sulphides dispersed through black mud ﬁlling a huge depression in the limestone. This was formed by acid from rotting pyrite dissolving the country rock. Extensive oxidation and remobilisation of the primary ores produced hundreds of thousands of tonnes of smithsonite, cerussite, malachite and azurite. Scores of rarer species, such as linarite, anglesite, brochantite, native silver and numerous arsenates were also present. Fig. 3. Malachite, from Tynagh, Co. Galway. 64mm x 35mm botryoidal and stalactitic mass dug out of the tips. Sadly, collectors were slow to learn of this treasure and most was sent to the crusher. By the time they did realise something glorious was going on, most was already turned into smelted metal. A fickle attitude on the part of management did not … Read More
Stephen Moreton (UK) In the second part of our tour of Ireland, we head for Munster, which occupies the southwest corner of the island. Geologically, the rocks are mostly inland Carboniferous shales and limestones, with Devonian sandstones forming the coastal peninsulas. All host mineral localities of note. Fig. 1. The four regions of the island of Ireland. Fig. 2. Munster in more detial. Starting in County Waterford, mineral collectors will tend to head for the copper coast – a group of nineteenth century copper mines centred on the coastal village of Bunmahon. The magnificent crystallised native copper and cuprite these mines yielded in the past are elusive nowadays. On the other hand, post-mining oxidation in the dumps and sea cliff levels and outcrops has produced an array of vividly coloured and sometimes rare secondary minerals. These include connellite, langite, atacamite, botallackite, brochantite, lavendulan and erythrite. The soft, wet, blue and green substances that coat the mine walls are amorphous gels that dehydrate and crumble to powder when removed to a dry environment. They are best left where they are. Fig. 3. Tankardstown Mine, Co. Waterford. The author is examining post-mining deposits of an amorphous copper-bearing gel. Mention should be made of the Croaghaun Hill beryl occurrence inland from the copper mines. In a small outcrop of conglomerate, one of many among the scrub, patches and sprays of slender, sky blue beryl prisms occur in a quartz matrix. Unfortunately, the rock is so tough it defeats even the largest sledgehammer. The … Read More
Jesse Garnett White (USA) “It is no measure of health to be well adjusted to a profoundly sick society” Jiddu Krishnamurti My Great Grandfather and his son both gave me some advice at a very young age. “Never trust anyone that won’t look you in the eye when they shake your hand” and “It’s OK to pick up hitchhikers while travelling the road”. These are all positive suggestions that have proved valuable both in the States and abroad. I’ve made a number of interesting decisions in my life. One I never thought I’d make was moving back to Alaska. I’ve told colleagues, dozens of friends, family members and myself, “I’ll never spend another winter in Fairbanks.”. Learning the lesson of ‘never say never’”, while travelling into the past and future simultaneously has been interesting to say the least. When a friend of 26 years heard the news, he said, “You can’t escape Covid-19, Jesse.” I completely blew that off and forged ahead. Since returning to Alaska, I’ve been fortunate to have worked with a lot of good folks, meet new friends, network, and travel around the interior and Alaska Range. I was blessed to work as a contract geologist at an open pit mine in both development and exploration roles, assist mom-and-pop miners with permitting, create an LLC, and work at what I consider the best pizza place in Alaska. Winter temperatures dipped below -50oF and snow depth at the cabin reached four feet in total. At the time of … Read More
Stephen Moreton (UK) The island of Ireland has much to offer the mineral collector, but is relatively unknown to most. This may in part be due to a lack of published information, although, for years, the troubles in the north also served to deter visitors for many years. This series of articles briefly summarises the principal mineral locations on a region by region basis. Fig. 1. The four regions of the island of Ireland. Fig. 2. Leinster in more detial. As the island is divided into four regions, Leinster, Munster, Connaught and Ulster (Fig. 1), which are in turn subdivided into counties, it seems appropriate to cover the island in this way. As the main ferry terminals for the Irish Republic are in Leinster many a trip to the country will start here. Leinster occupies the southeast region of the island and is the driest (or rather least wet) part of Ireland. Geologically, it offers the largest granite batholith in the British Isles, complete with metamorphic aureole, Carboniferous and Ordovician sediments and a scattering of basic igneous intrusions. County Wicklow dominates the mineral scene in Leinster. Fractures along the margin of the Wicklow granite have acted as conduits for much later mineralising solutions, giving rise to lead/zinc veins. These reach their best development in Glenmalure, Glendasan and Glendalough. Fig. 3. One centimetre spinel law twinned crystals of galena, from North Hero lode, Glendasan, Co. Wicklow. Fine schieferspar calcite and dark brown sphalerite have recently been found in Glendasan, while some … Read More
Helen Gould (UK) Following on from my articles on plate tectonics and the rock cycle, the tables below will hopefully be useful as an aide-mémoire to identify rock samples on your field trips. This table is intended as a field guide for budding geologists. Take it with you – and have fun. Fig. 1. (Right) Breccia; and (Left) Conglomerate. Fig. 2. (Right) Desert sandstone; and (Left) Micaceous sandstone. Fig. 3. (Right) Fliint; and (Left) Chalk. Fig. 4. (Right) Oolitic limestone; and (Left) Crinoidal limestone. Fig. 5. (Right) Siltstone; and (Left) Silt. Fig. 6. (Right) Quartzite; and (Left) Clay. Further reading Introducing Metamorphism, by Ian Sanders, Dunedin Academic Press Ltd, Edinburgh (2018), 148 pages (Paperback), ISBN: 9781780460642. Introducing Mineralogy, by John Mason, Dunedin Academic Press, Edinburgh (2015), 118 pages (Paperback), ISBN: 978-17-80460-28-4. Introducing Volcanology: A Guide to hot rocks, by Dougal Jerram, Dunedin Academic Press Ltd, Edinburgh and London (2011), 118 pages (Paperback), ISBN: 978-19-03544-26-6. Introducing Tectonics, Rock Structures and Mountain Belts, by Graham Park, Dunedin Academic Press, Edinburgh (2012), 132 pages (Paperback), ISBN: 978-19-06716-26-4. Planetary Geology: An Introduction (2nd edition), by Claudio Vita-Finzi and Dominic Fortes, Dunedin, Edinburgh (2015), 206 pages (Paperback), ISBN: 978-17-80460-15-4. Rocks and minerals: The definitive visual guide, by Ronald Louis Bonewitz, Dorling Kindersley (2008), 356 pages (hardback), ISBN: 978-14-05328-31-9. Other articles in this series comprise:Plate tectonics (Part 1): What are they?Plate tectonics (Part 2): A closer lookPlate tectonics (Part 3): The rock cyclePlate tectonics (Part 4): More on the rock cyclePlate tectonics (Part 5): A simple … Read More
After having favourably reviewed the first two books in this three part series, I must admit I was very much looking forward to the publication of this last one. And, of course, I wasn’t disappointed. This is the third in a series of guides to safe and responsible fossil collecting along (this time), the East Dorset coast from the Chalk cliffs at Bat’s Head, across what are some of Dorset’s more remote coastal locations, to Hengistbury Head.
Deborah Painter (US) The Los Angeles Times reported on 5 April 2021 that a magnitude 3.3 earthquake struck around 4:15a.m., followed by a magnitude 4.4 quake 29 minutes later. Several aftershocks followed. Seismologist Lucy Jones of the Lucy Jones Center reported that two quakes were 19.31km deep, with an epicentre around Inglewood, in the Los Angeles Basin. She reported that the movement was thrust, probably not on any mapped fault. Californians scarcely even notice an earthquake of magnitude 3.3 at that depth below the surface. That magnitude on the Richter scale is in the order of a large truck driving rather close by, but probably not intense enough to awaken them from sleep at that hour of the morning while being intense enough to warrant a news item. If one believes television programmes and movies, “The Big One” is going to happen sometime in the near future and part of California is going to slide into the Pacific Ocean and vanish beneath the waves, much like an overloaded barge. The trope of the sinking Golden State gained popularity sometime in the 1960s and should have been thoroughly discredited by now. The film industry helped get this into the general public’s mind and the general public keeps it alive. However, it would be impossible for two reasons: Firstly, tectonics is not going to cause the land to subside as though it were a huge chunk of the crust precariously teetering over the edge of the continent. California is firmly attached to … Read More
Helen Gould (UK) In Plate tectonics (Part 3): The rock cycle, I presented an overview of the relationship between the rock cycle and plate tectonics, and then went on to look more closely at igneous rocks. This time, I want to discuss sedimentary and metamorphic rocks, and review the occurrence of the rock cycle in the Solar System. Sedimentary rocks Sedimentary rocks, by contrast with igneous and metamorphic rocks, have no crystalline structure, being made up of little lumps of non-crystalline material derived from weathering other rocks. However, where they have been built up in horizontal layers, they may contain large-scale structures such as bedding. What are bedding planes? When sedimentary rocks deposited underwater (for example, limestones), they may be periodically exposed to the atmosphere due to tectonic uplift or a fall in sea level, perhaps because water is locked up on land as ice. The fact that it may take a thousand years to deposit a centimetre’s-worth of limestone places bedding planes into a context of millions of years. Fig. 1. Garnet micashist. Fig. 2. Garnet. Limestones are deposited in shallow seas, forming from the rain of billions of shells of sea animals onto the seaﬂoor. Deposition stops if the area is exposed to the air and restarts when the sea covers it again, so a gap (bedding plane) forms. Many sedimentary rocks are laid down underwater and may contain bedding planes. In addition, the grain size, the fossils that are present and other lithological features all may vary … Read More
Helen Gould (UK) What is the rock cycle? Usually, the first thing that budding geologists learn about rocks is that there are three kinds: igneous, sedimentary and metamorphic. These three major kinds are divided up into many different types of rock. For example, marble, slate and metaquartzite are all metamorphic rocks; basalt, granite, obsidian and andesite are all igneous rocks; and limestone, sandstone, clay and siltstone are all sedimentary rocks. What is a rock made of? Rocks are made of minerals. Therefore, particular combinations of minerals help us to identify rocks. Minerals are chemical compounds, consisting of chemical elements, which in turn are made of atomic particles. Who first thought of the rock cycle? James Hutton was the first geologist to propose a cycle of rock creation and change. In 1785, he gave a talk to the Scottish Geological Society in Edinburgh. In it, he suggested that rocks undergo processes that change them from one type of rock into another. He later developed the idea in his book, ‘Theory of the Earth with Proof and Illustrations’. He thought there was a relationship between the three basic rock types: igneous, sedimentary and metamorphic. We now know this is correct. Fig. 1. Agglomerate, Fig. 2. Andesite. However, it was not until this idea was set in a plate tectonics context that it really made sense to geologists. At about the same time, another Scotsman, James Hall, invented experimental geology. He demonstrated the crystallisation of basalt under slow-cooling conditions, and produced marble by … Read More
Dr Paul D Taylor (UK) There’s a small Cambrian trilobite (Fig. 1) that is collected in copious quantities from a site in the Wheeler Amphitheatre of Utah. Sold just as it is or mounted in jewellery, this trilobite lacks a common name and goes by its scientific name. In its fullest form, this is Elrathia kingii (Meek, 1870). But what exactly do the different parts of the name mean? How did Elrathia kingii – and other species of fossils – receive their names in the first place? And what are holotypes, lectotypes, neotypes and topotypes? In answering these and related questions, this article focuses on the procedures used by taxonomists when describing and naming living and fossil organisms. Fig. 1. The Cambrian trilobite species from Utah, now called Elrathia kingii (Meek, 1870), was originally named Conocoryphe kingii by Meek in 1870. Fifty-four years later, it was made the type species of the new genus, Elrathia by Walcott. Meek’s name is written in brackets because of this change in genus. Along with living organisms, the formal names of fossils employ the binomial system introduced by the Swedish naturalist, Carl Linnaeus in 1735. A genus name is followed by a species name, the latter sometimes referred to as the trivial name. Both are by convention always printed in italics, the genus name with a capital first letter and the species name with a lower case first letter. Unfortunately, newspapers all too often incorrectly print generic names with a lower case first letter. … Read More
Helen Gould (UK) As we saw last time (Plate tectonics (Part 1): What are they?), the Earth is a pretty dynamic place, with tectonic plates moving about on the surface, driven by convection cells in the upper mantle. But producing a workable theory, which combined most of the observations of geological evidence, took years. It was known that the centres of continents were extremely old, and that some areas around the continental “cratons” didn’t seem to belong because they contained completely different types of rocks. Combining continental drift with seaﬂoor spreading and mantle convection currents produced the idea of plate tectonics, and provided an explanation for the odd rocks on areas fringing some cratons. These “microplates” had come from other areas of the Earth, where different geological processes had produced different rock types. The role of density in recycling: oceanic and continental crust The physical features of the ocean basins and continental mountain ranges are known as the “crustal dichotomy” (splitting of the crust into two equal parts), and because these types of feature are essentially dissimilar, they have their own rock types. Basalt is the commonest rock both in the Solar System and on Earth, where it forms the ocean ﬂoor, along with various sedimentary rocks deposited underwater which make up another 5% of the total oceanic crust. Continents typically consist of coarse-grained rocks related to granites, which solidify below ground. Comparing similar-sized pieces of basalt and granite in the hand will establish obvious physical differences between them. Basalt’s … Read More
Helen Gould (UK) What does “plate tectonics” really mean? The Earth’s surface bears about 20 plates, which are able, over millions of years, to move about on layers beneath the crust. Some of the surfaces of these plates consist of continental crust, some of oceanic crust, some both (Fig. 1). Fig. 1. Map of the tectonic plates of the Earth. Who came up with the idea? The idea didn’t develop overnight as a result of one person’s efforts. In 1915, Alfred Wegener suggested “continental drift”, in which the continents moved around on the Earth’s surface. Arthur Holmes later suggested continents could be moved by convection currents in the mantle, fuelled by the heat of radioactive decay. Harry Hess was an American geologist who came up with the idea of seaﬂoor spreading. In the 1960s, J Tuzo Wilson developed the convection current idea further, proposed “hot spots” and “plates” and, in 1963, Fred Vine and Drummond Matthews proved the existence of seaﬂoor spreading using “magnetic striping”. What proof is there that plate tectonics really exists? The ﬁt of continents against each other, particularly Africa and South America, shows that they were once joined (Fig. 2). This branch of geology – palaeogeography – has led to the detection of several ancient supercontinents and oceans. Their existence is supported by matching similar geological features, such as ancient crystalline rocks and glaciated areas, in adjacent regions of South America and Africa, and North America and Europe. Two massive continents, which existed in the past, … Read More
Mike Thorn (UK) In his book, “Architects of Eternity: The New Science of Fossils”, Richard Corfield coins the term “reluctant palaeontologists”. He has in mind those chemists, biochemists and biologists who use the techniques and skills from their own disciplines to shed new light on our ideas about evolution. Ross Barnett, of the Department of Zoology at Oxford, might well be considered to be in this category. A biochemist by training, he has recently co-authored a paper on the DNA of three extinct cats which has helped to lay to rest some of the arguments about the feline family tree. Fig. 1. Smilodon skeleton. Ross came to Oxford in October 2002, to work on a PhD, after completing his biochemistry degree at Edinburgh. His supervisor, Professor Alan Cooper, was interested in cat genetics and had managed to raise funds to carry out research into the relationships of several extinct cats. In particular, there were questions about where the sabre-toothed cats, such as Smilodon and Homotherium, fitted in. Fig. 2. Ross Barnett in his office. As Ross explained: There has been a lot of study done on these animals. For example, there is a huge collection of thousands of individuals of Smilodon from Rancho Le Brea in Los Angeles, so they’ve been really well characterised from their morphology. What the palaeontologists had concluded from this was that there was a split at the base of the cat family tree between the group that goes on to form the sabre- tooths – … Read More
Jon Trevelyan (UK) If Yorkshire really is ‘God’s Own County’, then clearly the Almighty is an enthusiastic geologist. Just how lucky is the Yorkshire man who, on the same day, can see some of the best and most varied geology in the world, set out in glorious coastal and mountain … Read More
This small, yet informative, booklet takes you on a four-mile walk to 13 sites and through 15 million years of Earth history. The Mortimer Forest Trail is a geology trail in Shropshire that is famous for its outstanding fossils and varied geology. The trail mostly examines Silurian formations such as the Wenlock and Ludlow series.
James O’Donoghue (UK) Did the destruction of forests by mammoths make the Pleistocene Ice Age even colder? It’s an extraordinary prospect. Yet, a leading fossil mammal expert thinks they did just that. Over many tens of thousands of years, mammoths and straight-tusked elephants ate their way through vast tracts of the world’s forests. Trees exert a buffering effect on global climate – take them out and face the prospect of hotter and colder extremes. Mammoths may have turned cool Ice Age periods into freezing ones. Straight-tusked elephants may have made temperatures rise during interglacials. Both types of elephant had all but vanished by 10,000 years ago, never to return. Since then, forest cover has increased sharply while the climate has been unusually mild and stable. Could the two be linked? Humans chopping down forests are now exerting at least as profound an effect on the world’s ecosystems as the mammoths had on theirs. By comparing the destruction wrought then and now, an alarming prospect emerges. Are we in the very process of making our own climate as volatile as that of the extinct elephants? Cores drilled from undisturbed glacial ice in Greenland and Antarctica have provided a wealth of information about almost constant shifts in the Earth’s climate over the past few hundred thousand years. Climatologists will tell you that we live in an interglacial period, in a world that is still going through an ice age that started 1.8Ma with the onset of the Quaternary period. (When I refer … Read More