Is the Core Separate from the Mantle - Maybe Not

A correspondent sent me THIS LINK which looks at new evidence suggesting that material from the core is getting into the mantle and, eventually, to the Earths surface.

We have long been taught that the lighter mantle floats above the denser metallic core and that there cannot be movement between the two (except for earthquake waves).

But work on helium isotopes casts doubt about the separation. Helium-3 was formed just after the Big Bang and was confined to deep in the Earth, some believed it was confined to the core. Helium-4 is formed from the decay of uranium and thorium and is confined the mantle and the Earths surface. But then Helium-3 was found in volcanic lavas from mid-ocean ridges.

Ruthenium is an element with an affinity for iron and thus is concentrated in the iron-rich core. This applies particularly to Ruthenium-100. Other ruthenium isotopes came to Earth later via meteorites but Ruthenium-100 should be confined to the core. But it is now found at the surface.

So how is the core stuff getting into the mantle? Debate rages with a lot of attention being paid to two huge "blobs" - one under the Pacific and the other under Africa. These are believed to be hot but dense and supplying plumes leading to the surface. Are they "mining" the core or are they a bridge from the core to the surface.

Expect to hear more about this in the future.

 Down to Earth Extra August 2025

The August 2025 edition of Down to Earth Extra has been published. You can download it HERE or you can read it below.

 The Grand Canyon - Then and (Almost) Now

My attention has been drawn in the last week to two articles both concerning the Grand Canyon. THIS ARTICLE was sent to me by a correspondent - thank you - and concerns well preserved fossils from the middle Cambrian (Bright Angel Formation) 505 million years old, found in the Grand Canyon, and THIS ARTICLE which suggest that the meteor impact which created Meteor Crater, 100 miles from the Grand Canyon, caused landslides which dammed the canyon. This happened 56,000 years ago - almost yesterday!

The Cambrian fossils found are slightly younger (3 million years only!) than those of the Burgess shale and are mainly priapulid worms with some crustaceans and molluscs. They show that life was innovating new forms. The source paper can be found HERE and has some wonderful pictures of the beautifully preserved (but tiny) fossils.

Crustacean sternal elements from the Bright Angel biota.

Paragnath-bearing triangles are indicated by 1 s, and the successive posterior triangles by 2 s. (A) Posterior end of paragnath-bearing triangle and anterior section of successive triangle. (B) Complete triangle with laterally splayed paragnaths (black arrows). (C) Detail of scaly ornament of median cuticular strip in (B). (D) Detail of anterior setose surface in (B). (E) Complete paragnath-bearing triangle, with articulated anterior section of successive triangle. (F) Detail of boxed area in (E) showing scale-bearing cuticular strip and marginal setal fringes. (G) Articulated paragnath-bearing and partial posterior triangles defining median food groove. (H) Detail of boxed area in (G) showing sphaeromorphic acritarch adpressed onto the food groove cuticle. (I) Subtriangular cuticular lobe, representing possible setulose labrum. (J) Complete paragnath-bearing triangle and articulated, semi-complete posterior triangle. (K) Detail of boxed area in (J) showing spheroidal acritarch adpressed onto the food groove cuticle. Slide numbers and England Finder coordinates listed in data S1. Scale bars, 50 μm except in (C) and (H) (5 μm) and (D), (F), and (K) (25 μm).

The evidence for the damming of the Grand Canyon is not controversial. There are caves 45m above the river which have driftwood logs in them. In the last few years improved dating techniques have been used and they show that the ages of the damming and the meteor impact are about the same. Whether one caused the other is rather more difficult to prove.

Terror Bird Meets it's Doom

A correspondent sent me THIS LINK (I had seen it too!), concerning a dramatic event which happened 13 million years ago in the Middle Miocene.

This was in, what is now, Colombia. The locality is a desert (the Tatacoa Desert), then it was a swamp. A local collector had found the fossil and exhibited it in his own museum. Researchers from a Colombian university were cataloging the collection and discovered two things. The first was that the fossil was a leg bone from the top, land based, predator of the time Phorusrhacinae sp, better known as the Terror Bird. Fossils of this bird are rare, but what was even more exciting was the presence of tooth marks on the bone.

The tooth marks are similar to the teeth of crocodile-like creatures whose fossils can be found in museum collections. The most likely candidate is Purussaurus neivensis which was among the top, water based, predators of the time.

The tooth marks show no sign of healing and suggest that the Terror Bird did not survive, or that it was dead already and the croc scavenged it. (In scientific language being eaten is a trophic event!)

The story gives a fascinating glimpse of life in the past.

 Field Trip Proposal by Nick Chidlaw

Nick Chidlaw is proposing to run a field trip entitled:-

GEOLOGY OF THE PERMIAN STRATA OF COUNTY DURHAM, NORTH EAST ENGLAND

which sounds rather good. He introduces it as follows:-

-------------------------------------

June 2025 

Dear All,  

It has been very gratifying the level of interest and enrolments on the courses and field trips I have proposed and run during last year, and to learn from a number of attendees, particularly on recent events, that they would be interested in further field-based ones during 2025. 

I am proposing a 4 day field trip, to be run in late October this year, which interested parties may be available to attend. This focuses on the Permian strata of County Durham, in NE England. People who’ve studied Permian rocks in the S of England (exposed extensively in eastern Devon) will note that these were 

formed in a continental desert environment, under a hot dry climate. The crust that became the British Isles was located just N of the equator; the Permian period extending from 299 to 252 Ma. Other strata deposited under similar conditions of this age occur extensively in parts of SW and S Scotland, and NW 

England.  

Such continental sediments also occur in NE England, but are overlain by thicker and more extensive marine strata of this age. Outcrops of marine Permian occur locally in other parts of Britain, but are very small compared with that found in County Durham. It is in the latter that study of a wider range of Permian environments can be made than elsewhere in Britain. All these strata in County Durham have greater affinity with those of a similar age in mainland Europe, together with the area in between under the North Sea (known from hydrocarbon exploration): some of the stratigraphic names in County Durham reflect this, utilising terms applied in Germany. The Permian strata in County Durham are impressive, reflecting a range 

of environments that were highly diverse. In addition, the effect of post-depositional changes to the marine Permian rocks of the area are striking: from the development of bizarrely-structured concretions in carbonate deposits, through wholesale dissolution of evaporite stratigraphic units, to the formation of collapse structures and breccias in the rocks overlying these formerly-present strata.     

On the proposed field trip, two days visit locations inland, and two days to coastal locations. Tidal conditions on the two coastal dates are optimum to allow visits to be carried out safely and for longer than otherwise.       

This part of England is perhaps perceived by some who have not so far visited it, to be unattractive in appearance, it being a key location in Britain’s past for heavy industry, particularly ship-building and coal mining.  In actuality, the environment is largely agricultural, with a highly attractive coastline, and negative 

features on the landscape from these past industries have essentially been removed.  I have travelled widely in County Durham, the infrastructure is modern and well–developed, and urban areas whether large or small, are for the most part pleasant in appearance.     

Accommodation Factor  

Ideally, enrollees would arrange accommodation on or near to the coastal area, thereby minimising time needed to travel to most locations each day of the itinerary. This field trip was previously run in June 2019, and when arranging it earlier that year we discovered that a lot of available accommodation in the coastal 

area (the ideal location for the trip) had already been booked up. Some of the field party then had to arrange accommodation further inland, resulting in longer travel times to get to and from most of the field locations.  

The dates of the current proposal, being in late October, will hopefully allow for more accommodation to be available than during summer months, and enrollees may be able to book nearer to, or on, the coast.  

These dates are also chosen to avoid booking Friday and Saturday nights which will be attractive to people 

wanting to stay in the area just for a weekend.  

Tidal and Daylight Factors  

A number of key locations to be visited on this field trip are coastal and subject to tidal conditions. The dates proposed take this into account, enabling safe access to exposures for as long as possible.  

The dates are within Greenwich Mean Time (GMT), the clocks having just changed from British Summer Time going back 1 hour. This means sunset will be at around 4. 40 pm. We would ensure we complete the itinerary each day while enough daylight remains; this could involve starting the itinerary earlier each day: field events I run usually have a programme of geological study between 10.00 am and 5.00 pm; this could be adjusted to 9.30 am – 4.30 pm so that everything is completed in good time.  

I hope you find the proposal (see below) of interest and are available to attend. I look forward to hearing 

from you.  

Regards, 

Nick Chidlaw nickchidlaw@gmail.com  

------------------------------------

Nick gives very full details of the trip which are too long for this blog post. You can download it in its entirety HERE.

 Visit the Holm Islands

Dr. Nick Chidlaw has proposed a trip to Steep Holm and Flat Holm. He has written an extensive introduction to the trip which I have repeated below. It sounds rather good.

-------------------------------------

Dear All,

I am currently proposing a trip to study during 1 day the geology of the Holm Islands; these are located in the sea where the Severn Estuary and Bristol Channel meet. 

There are 2 islands, Steep Holm and Flat Holm, the former being part of England, and the latter Wales.  

I have run trips to study the geology there in the past, and they have enrolled well and attendees have greatly enjoyed visiting the islands and studying the geology.  I have also run indoor courses and given talks on the subject, and they have gratifyingly drawn good responses too. 

The plan is to duplicate as far as practical the field programme used on earlier trips.  This involves landing on Flat Holm, and studying the geology in beach sections and local crags, and sailing around Steep Holm, observing the geology from close inshore but not landing. This plan for Steep Holm is because most of the geology is best observed in its steep cliffs around the island; when on Steep Holm itself, much of this geology is not saffely accessible.  The sailing around Steep Holm is not done quickly - we spend over an hour going around, with many stops during which we discuss the geology visible at each key point.  

The rocks on both islands are of early Carboniferous age, mostly shallow marine with some indicating episodic emergence. The lithologies are limestones and dolostones with variations in grain size and shelly fossil content, and minor non-carbonate mudrocks. On Flat Holm is a limestone unit known only from that island. Many of the stratigraphic units can be linked to the nearby mainlands of England at Weston-Super-Mare, and in the Barry area in Wales.  The strata are extensively deformed by compressional folding and faulting that occurred during the Variscan Orogeny around the end of Carboniferous times c. 300 million years ago: on Steep Holm, the strata mostly dip gently to the S, but become steely-inclined,  in places 70 degrees, on its northern side; on Flat Holm, the island is mostly occupies a gentle upfold, plunging to the south west. There are reverse faults observable on Flat Holm together with minor folds superimposed on the main fold, and some impressive ripple structures in the limestone unique to Flat Holm. During the Triassic period, under a hot dry climate, the two islands formed 'inselbergs' surrounded by extensive flats that episodically became lakes. Crustal stretching during the Middle Jurassic c. 170 million years ago carried metalliferous brines up opening faults on Steep Holm, locally depositing galena and baryte. Before the end of the last glacial, c. 12,000 years ago, the sea was much further to the west, and the islands formed hils, between which the River Severn flowed in a narrow ravine some 45m below present sea level. With the ending of the last glacial, sea level rose to form the Bristol Channel and Severn Estuary, leaving the Holms as the islands we see today.

Date of the proposed trip

Saturday 30th August 

Transport & organisation

Rigid Inflatable Boat (RIB) operated by Bay Island Voyages Ltd out of Cardiff Bay.   It is to be appreciated that if the sea conditons on the day are unsuitable, the company will decide to cancel / postpone the trip for reasons of safety. 

Timings     

The Bristol Channel and Severn Estuary have some of the highest tidal ranges in the world; as can be appreciated, the proposed itinerary is strongly governed by predicted tidal conditions and currents. On this proposed date, the activities take place from 8 am, with the field party returned to Cardiff Bay by 2 pm.

The details are as follows :

0800     Meet at Cardiff Bay (check in, safety briefing, life jacket fitting. 

0830     RIB passes out through Cardiff Bay Barrage 

0850     Arrive at Flat Holm. Landing fee £5.00 per person (cash only, payable on arrival). We are allowed c. 2.5 hours on the island 

1120     Depart Flat Holm

c.1145  Arrive Steep Holm - circumnavigate island, with frequent pauses, for c. 1.5 hours. 

1315     Depart Steep Holm

1345     Pass through Cardiff Bay Barrage 

1400     Arrive Cardiff Bay

Fee

The fee involves payment to Bay Island Voyages Ltd for providing private charter transport, and tuition by myself. 

I will pay Bay Island Voyages their fee, from fees received from those who are interested and available to attend the trip. 

There are 12 places available on the RIB, 11 trip attendees and myself.  

The fee per person £125.00 

In case there is a good number of people interested and available, enrolments will need to be on a first-come first-served basis. 

If there are fewer than 11 who can attend the trip, the cost is likely to be too high per person if the private charter fee is shared between those who can attend; we will need to cancel the proposal should this be the case. 

If there are more than 11 who are interested and available to attend the trip, they can be put on a waiting list and Bay Island Voyages Ltd have said there may be another RIB available, but they do not know at the present time.  

If the trip can go ahead, I will sent a PDF of the trip document to all those enrolled in good time before the date of the trip. This will provide all logistical information attendees will need (including location of Bay Island Voyages car parking area and embarkation point) plus geological background. Attendees would bring printouts of the trip document with them for reference during the days programme. 

Viability Deadline

Bay Island Voyages Ltd has a busy programme, but they are helpfully prepared to operate a provisional booking with us for 2 weeks up to 14th July.

I must therefore make a definite booking with them, and pay their fee, by this set date.  If the payment and booking is not secured by that date, they will make the RIB avaiable to other potential users for 30th August. 

Payment to me

 

If you are interested and available for this trip, please forward me your fee of £125.00 by Saturday 12th July. 

I will let you know on Saturday 12th July if we can put the trip on. If we do not have enough enrolments, I will return your fee the same day. 

Please note enrolment requests are to be sent to:

Nick Chidlaw <nickchidlaw@gmail.com>

Some images are given below to illustrate the islands and the transporting vessel used. 

I hope you find this proposal interesting and that you can attend.  Any queries you may have, do let me know.

Holm Islands from South Wales

Flat Holm

Steep Holm

Holm Islands RIB

-----------------------------------------------

 The Oldest Meteorite Impact - Not Quite

A correspondent has sent me THIS LINK which concerns a meteorite impact in Western Australia. The "Science Alert" article is based on THIS ACADEMIC PAPER and is also the subject of 

THIS ARTICLE.

The burden of the article is that it refutes an earlier PAPER which claimed that the impact was the earliest known on Earth. The original dating was based on the very old age of the rocks in which cone structures were observed and an age for the impact of 3.47Ga. 

The later paper tells us that, in the same area, shatter cones have been found in younger rocks aged at 2.77Ga and they conclude that the maximum age of the impact is 2.71Ga - and the minimum a meagre 0.4Ga.

These papers are examples of the scientific method at work. I also note that the article in THE CONVERSATION illustrates its argument about superposition by using a photograph of the Siccar Point unconformity - the earliest described unconformity. Do I detect someone poking fun at the competition!