Down to Earth Extra July 2023

The July 2023 edition of Down to Earth Extra has been published. You can download it HERE or you can read it below.

 When was the First (Placental) Mammal?

There are three sorts of mammals: monotremes (platypuses), marsupials (kangaroos) and placentals (us and lots more).

How do you find the first placental mammal? I suppose you could find its fossil, be able to determine it is placental, date it, and (the difficult bit) prove that there are none which came before. This is unlikely and your conclusions are likely to be challenged. 

However there are a few fossils which are accepted as being placental mammals dated as living after the extinction of the dinosaurs. But were they the first? Were there placentals living alongside the dinosaurs? There are no accepted placental fossils in rocks below the K-Pg boundary, but that does not prove much.

There is another way, using molecular clocks. Much has been written about the use of molecular clocks - the more you get into it the more difficulties appear. See the diagram below to get a flavour of the controversies.

Thick purple lines are crown orders, green lines are stem orders, and black lines are stem placental families.

(A) Explosive model: all placental mammal diversification and origination occurred just after the K-Pg boundary.

(B) Soft explosive model: placental mammals originated just before the K-Pg boundary, but intraordinal diversification only occurred after the boundary.

(C) Trans-KPg model: both interordinal and intraordinal diversification occurred around the K-Pg boundary.

(D) Long fuse model: placental mammals originated in the middle of Late Cretaceous, but intraordinal diversification did not begin until after the K-Pg boundary.

(E) Short fuse model: placental origination and crown order diversification occurred during the Cretaceous.

The author of THIS ARTICLE, working at Bristol University, has avoided much of these controversies by comparing families and using statistical methods, of which I know little, to conclude that placental mammals originated in the Cretaceous

The article is based on THIS ACADEMIC PAPER. An indication of the depth of study used in the article can be gauged from the following figure.

Clade age and extinction time estimates for placental mammal families

Each line represents a family (arranged by order and clade but without further phylogenetic information), with 95% credible intervals in colors at the root estimates and extinction estimates (where applicable). Gray lines fill in the lineage. 93 families have credible intervals extending into the Cretaceous, but many originated after the K-Pg boundary. For stem and crown order classifications for each family, see Data S1.

 Does Banded Iron Formation Cause Mantle Plumes?

It seems a stretch to connect a sedimentary rock, which needs life to form, is connected with things happening at the core/mantle boundary. Surface life affecting the very deep Earth.

The cause, if it exists, is the density of BIF (Banded Iron Formation). BIF density is about 3.5t m⁻³, which is rather heavy for the rocks found at the Earths surface.

What would happen if BIFs were subducted? They would sink and keep on sinking and eventually reach the Core/Mantle Boundary. Their high iron content and the associated high conductivity might encourage heat transfer from the core causing mantle plumes and Large Igneous Provinces.

You can read an introduction to this scenario HERE. It is inspired by THIS ARTICLE in Nature.

Banded Iron Formation

 How Did Dinosaurs Grow?

A correspondent sent me links to three articles which he found interesting. This blog post concerns THIS ONE. The others, which are beyond my skill to write about, but certainly look interesting, are HERE and HERE.

Do dinosaurs (or other animals) grow quicker and faster or slower and longer - the answer is both. Fast growers can out-compete other species but they need lots of food. Slow growers face more risks but they can get through hard times.

But how do you study this? By looking at their bones! (As that is, for the most part, all that you have got, it is the obvious answer.) Theropod bones were sliced and polished down to wafers the researchers could see through. And then the growth rings could be studied - similar to tree rings.

It was found that some species grew larger over time, while others grew smaller, but there was no consistency - except in the case of the species which led to birds. Presumably being smaller makes flying easier.

The speed of growth does not determine eventual size - slow growers can be as large as fast growers, it just takes longer.

Dave Green's Geology and Landscape Walks 

Dave Green has just sent out his programme of summer walks. Read all about it below.

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Geology and Landscape

 

of Gloucestershire and surroundings

 

A weekly field-based introductory course.

 

No previous knowledge of geology is assumed

 

Tuesday evenings

6^th June to 11^th July 2023

 

Gloucestershire is one of the most geologically diverse counties in Britain.

 

The aim of this field-based course is to take you towards an 

understanding of local scenery.  We will look at the components

- the highly diverse  rocks and their structure; and processes

- weathering, slope forming and erosion - which have combined to

produce this equally varied landscape - the materials from

which the scenery has been sculpted and the processes that have acted

upon them since the area emerged from the sea 65 million years ago

(about the same time that the dinosaurs became extinct)

 

No special equipment is necessary, apart from stout footwear and

possibly waterproofs - although we will hopefully have six balmy

summer evenings! Meetings are held on Tuesdays each week,

 meeting at 7.00 pm and finishing at 9.00 pm or later

 (whenever the party feels in need of refreshment !!) at the

 following meeting points (see below)

 

 

Cost: £50 for 6 week course

or £10 per session

 

For further details see over or telephone

Dave Green on 01594 860858

Email Davegeostudies@gmail.com

 

Geology and Landscape 2023

6^th June Tresham  

South of Wotton under Edge, this small village lies at the head of one of the valleys cut into the Cotswold escarpment, on limestones lying above the Fullers Earth Clay; infamous for its tendency to produce landslides and mudflows. The limestones include the Tresham Rock, Athelston Oolite and the biggest area; Forest Marble, which caps the escarpment at this point, above Hens Cliff.The steep-sided, deeply incised valleys cutting into the scarp  contrast with the gentle sided dry valleys cut into the Cotswold dip slope during the Ice age. We will examine the form of these valleys as well as a superb section from the Fullers Earth down, and the contrast between the scarp and dip slopes.

 Meet at the minor roadside, east of the church (ST 794912), parking tidily (at 90^o to road, if possible should there be a lot of cars) on the verge where there is hard standing.

 

13^th June Plump Hill

Known for spectacular views across the Severn Vale, Plump Hill lies on the steeply inclined eastern limb of the Forest of Dean coalfield. Because of the steepness of the dip of the rocks (Old Red Sandstone and Carboniferous), all the Forest rocks are exposed within a short distance of one another. The steep slope out of Mitcheldean on the A4136 is due to the resistance of the rock forming the outer rampart of the Forest – the Quartz Conglomerate, outcrops and huge detached blocks of which can be seen on the way up. Many of the varied rocks are exposed here, thanks to extensive exploitation in the past for various purposes. We aim to examine the rocks, the past activity and the views, by means of a circular walk, avoiding the road as far as possible.

Meet at the car park off the north side of the A4136 beyond the last cottages [coming from Mitcheldean](SO 659 170).

 

20^th  June Selsley Common and Bown Hill

The Cotswold escarpment, capped by the Inferior Oolite limestone is well displayed here, in its normally wooded cloak and as bare common. Above the common and the deep Woodchester Park valley lies the Fullers Earth outlier of Bown Hill, illustrating well the stepped, layered nature of much of the scarp scenery.  There are fantastic views across the Severn Vale, across the Frome valley to Stonehouse and Doverow Hill and across the Nailsworth and woodchester valleys. We will take a short circular walk to illustrate the relationship between the various rock types and the landscape they produce.

Meet at the small car park by a dew pond at the southern end of Selsley Common, near the cattle grid. (SO 825 024)

 

 

27^th June Newent Coalfield, Oxenhall

We will examine the remnants of part of the tiny Newent coalfield, once incorrectly heralded by Roderick Murchison as having enormous potential wealth extending beneath the Severn Vale, and also the effects on scenery of the local version of the Malvern Fault and the Triassic rocks in the area to the north of Newent – the home of Dick Whittington! Two or three sites will be visited, by car. Walking will be minimal, car sharing is to be encouraged, with narrow lanes and limited parking.

Meet at a very small (park tidily at 90^o to road!) lay-by/field entrance with old sleepers as a fence on the minor road from Oxenhall to Gorsley ,  100 metres SW of White House SO696268

 

4^th July Wickwar

Wickwar is built on the horseshoe-shaped ridge of Carboniferous Limestone that fringes the North Bristol (Coalpit Heath) coal basin, a syncline formed by the Variscan continental collision 300Ma ago at the end of the Carboniferous. Apart from a different climate (hot desert), and absence of the Cotswolds, the landscape would have looked remarkably similar 200 million years ago at the close of the Triassic period. Limestones form the most resistant rocks, standing above the weaker Coal Measures to the west and Old Red Sandstone with older rocks to the east. The whole landscape was subsequently buried beneath at least a kilometre of Mesozoic rocks, which are now being stripped off by modern erosion – a process known as “exhumation” of the ancient landscape. We will attempt to illustrate the rocks and scenery by means of a circular walk of approximately 4.3km.

Meet in the car park of the Fox and Maple (formerly the Buthay), Wickwar (ST 725 886)

 

11^th July West Malvern to Stiffords Bridge

The Malverns represent a window into what lies deep below the rest of England and Wales – its Pre-Cambrian basement, which is normally hidden beneath great thicknesses of younger rocks. These ancient igneous and metamorphic rocks were brought up from the depths during the violent collision of continents that produced the Variscan mountains 300 million years ago. They were pushed westward and upwards during the collision, rucking the overlying Cambrian, Silurian and Devonian rocks to the west up into a series of folds, repeating their outcrops and therefore the ridges and valleys produced by modern erosion. We will aim to illustrate these features by a linear walk of approximately 4.5km

Meet at the car park of the Red Lion, Stiffords Bridge on  A4103 (Worcester-Hereford road) (SO 766 382)

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 Kimberlites Come From Great Depths - Computers Confirm.

THIS ARTICLE reports on computer studies of the Earth's mantle. These show, using methods which I cannot pretend to understand, that giant pillars of heat, rising from just above the planet's core, provide the energy and some of the contents - including diamonds! - for kimberlites.

The researcher's work can explain many, but not all, of the earths kimberlites and predicts where more may be found.

The mechanics are complex and difficult to visualize - see the short video below.

The diagram below makes it easier to understand but, no doubt, misses many of the complexities.

Down to Earth Extra May 2023 

The May 2023 edition of Down to Earth Extra has been published. You can download it HERE or you can read it below.