Scientists have traced Earth’s path through the galaxy via tiny crystals found in the crust

Below is an article we wrote on The Conversation about our work on the formation of continents on the Early Earth and the movement through the Milkyway galaxy:

“To see a world in a grain of sand”, the opening sentence of the poem by William Blake, is an oft-used phrase that also captures some of what geologists do.

We observe the composition of mineral grains, smaller than the width of a human hair. Then, we extrapolate the chemical processes they suggest to ponder the construction of our planet itself.

Now, we’ve taken that minute attention to new heights, connecting tiny grains to Earth’s place in the galactic environment.

Looking out to the universe

At an even larger scale, astrophysicists seek to understand the universe and our place in it. They use laws of physics to develop models that describe the orbits of astronomical objects.

Although we may think of the planet’s surface as something shaped by processes entirely within Earth itself, our planet has undoubtedly felt the effects of its cosmic environment. This includes periodic changes in Earth’s orbit, variations in the Sun’s output, gamma ray bursts, and of course meteorite impacts.

Just looking at the Moon and its pockmarked surface should remind us of that, given Earth is more than 80 times more massive than its grey satellite. In fact, recent work has pointed to the importance of meteorite impacts in the production of continental crust on Earth, helping to form buoyant “seeds” that floated on the outermost layer of our planet in its youth.

We and our international team of colleagues have now identified a rhythm in the production of this early continental crust, and the tempo points to a truly grand driving mechanism. This work has just been published in the journal Geology.

A swirling spiral of blue and white glowing stars on a dark background
Residing inside the Milky Way galaxy makes it impossible to picture, but our galaxy is thought to be similar to other barred spiral galaxies, like NGC 4394. ESA/Hubble & NASA

Read more: What created the continents? New evidence points to giant asteroids

The rhythm of crust production on Earth

Many rocks on Earth form from molten or semi-molten magma. This magma is derived either directly from the mantle – the predominantly solid but slowly flowing layer below the planet’s crust – or from recooking even older bits of pre-existing crust. As liquid magma cools, it eventually freezes into solid rock.

Through this cooling process of magma crystallisation, mineral grains grow and can trap elements such as uranium that decay over time and produce a sort of stopwatch, recording their age. Not only that, but crystals can also trap other elements that track the composition of their parental magma, like how a surname might track a person’s family.

With these two pieces of information – age and composition – we can then reconstruct a timeline of crust production. Then, we can decode its main frequencies, using the mathematical wizardry of the Fourier transform. This tool basically decodes the frequency of events, much like unscrambling ingredients that have gone into the blender for a cake.

Our results from this approach suggest an approximate 200-million-year rhythm to crust production on the early Earth.

Read more: Ancient Earth had a thick, toxic atmosphere like Venus – until it cooled off and became liveable

Our place in the cosmos

But there is another process with a similar rhythm. Our Solar System and the four spiral arms of the Milky Way are both spinning around the supermassive black hole at the galaxy’s centre, yet they are moving at different speeds.

The spiral arms orbit at 210 kilometres per second, while the Sun is speeding along at 240km per second, meaning our Solar System is surfing into and out of the galaxy’s arms. You can think of the spiral arms as dense regions that slow the passage of stars much like a traffic jam, which only clears further down the road (or through the arm).

Geological events on the orbit of the solar system in the Milky Way galaxy
Geological events, including major crust formation events highlighted on the transit of the Solar System through the galactic spiral arms. NASA/JPL-Caltech/ESO/R. Hurt (background image)

This model results in approximately 200 million years between each entry our Solar System makes into a spiral arm of the galaxy.

So, there seems to be a possible connection between the timing of crust production on Earth and the length of time it takes to orbit the galactic spiral arms – but why?

Strikes from the cloud

In the distant reaches of our Solar System, a cloud of icy rocky debris named the Oort cloud is thought to orbit our Sun.

As the Solar System periodically moves into a spiral arm, interaction between it and the Oort cloud is proposed to dislodge material from the cloud, sending it closer to the inner Solar System. Some of this material may even strike Earth.

A glowing image of a spiral galaxy with blue arms and pale golden centre
Milky Way’s structure and Solar System’s orbit through it may be important in controlling the frequency of some large impacts on Earth, which in turn may have seeded crust production on the early Earth. jivacore/Shutterstock

Earth experiences relatively frequent impacts from the rocky bodies of the asteroid belt, which on average arrive at speeds of 15km per second. But comets ejected from the Oort cloud arrive much faster, on average 52km per second.

We argue it is these periodic high-energy impacts that are tracked by the record of crust production preserved in tiny mineral grains. Comet impacts excavate huge volumes of Earth’s surface, leading to decompression melting of the mantle, not too dissimilar from popping a cork on a bottle of fizz.

This molten rock, enriched in light elements such as silicon, aluminium, sodium and potassium, effectively floats on the denser mantle. While there are many other ways to generate continental crust, it’s likely that impacting on our early planet formed buoyant seeds of crust. Magma produced from later geological processes would adhere to those early seeds.

Harbingers of doom, or gardeners for terrestrial life?

Continental crust is vital in most of Earth’s natural cycles – it interacts with water and oxygen, forming new weathered products, hosting most metals and biological carbon.

Large meteorite impacts are cataclysmic events that can obliterate life. Yet, impacts may very well have been key to the development of the continental crust we live on.

With the recent passage of interstellar asteroids through the Solar System, some have even gone so far as to suggest they ferried life across the cosmos.

However we came to be here, it is awe-inspiring on a clear night to look up at the sky and see the stars and the structure they trace, and then look down at your feet and feel the mineral grains, rock and continental crust below – all linked through a very grand rhythm indeed.

Work experience week 2022

Study Physics in Lincoln

Last week the School of Mathematics and Physics hosted 5 work experience students from Lincoln University Technical College, Branston Community Academy and William Farr.

The aim of the week was to give a taste of what it would be like to study Mathematics or Physics at the University of Lincoln (or elsewhere), and for the students to gain some experience related to working in a university.

On Monday the students were given a tour of the University of Lincoln campus and the Isaac Newton Building in which the School of Mathematics and Physics is based. We also gave the students a very useful talk about the university application process and finances.

“We received some insightful information about how to make your
application stand out from other applications, how to know how much money you
will receive from loans and how to use student loans when living independently.”

On Monday afternoon…

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Physics Film Night after the pandemic – 30/3/2022

IOP Lincoln Centre

On 30 March 2022 Lincoln School of Maths & Physics and the University of Lincoln Maths and Physics Society hosted the  Physics Movie Night, the first such event after the pandemic. It took place for most of its time in the Stephen Langton Building Lecture Theatre and finished for the last 10 minutes in our own INB3305 room in the Isaac Newton Building. The movie screened was Interstellar, which was the subject of discussion in our 3rd year Physics module “Physics of the Universe”. The night started at 6:30pm with a discussion and pizzas.

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Physics Film Night – 18/5/2022

IOP Lincoln Centre

Lincoln School of Maths & Physics and the University of Lincoln Maths and Physics Society are happy to invite you to the Physics Movie Night, the second one after the pandemic.

Date: Wednesday, 18 May 2022
Film: Contact (1997)
Stars: Jodie Foster, Matthew McConaughey
IMDB: 7.5/10; Awards: 15 wins & 27 nominations
Genre: Drama, Mystery, Sci-Fi
Details: 2h 30min, PG
Where: The Swan, Lincoln 
Time:  Doors open 19:30

A fascinating film about the search for extraterrestrial intelligence (SETI).

The night will start with a discussion and pizzas.

You are welcome to read  a short introduction to the Lincoln Astronomical Society given by Dave Castledine almost 6 years ago at the previous screening of this film.

Spaces are limited and the access is by the reservation through University of Lincoln Maths and Physics Society .

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From War And Peace To The Moon

How to grow a moon, and understanding the evolution of war and peace.

This event will include a viewing of some of our Creative Reactions artworks – art inspired by our Pint of Science speakers’ research.

May 9th 2022

Doors 7pm
Event 7.30pm to 9.30pm
The Pessimist, 4 Mint Lane,
Lincoln LN1 1UD

How to grow a moon

Dr Phil Sutton (Senior Lecturer in Astrophysics)

Most planets in our Solar System have moons orbiting them. The search is on to find moons orbiting planets outside of our solar system, known as exomoons, due to their potential for supporting life. But how do moons form and end up where we find them? This talk will consider some scenarios that can lead to planets having moons, like planetary impacts and gravitational capture.

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Evolution of war and peace

Prof Bino Majolo (Professor of Social Evolution)

Scientists and philosophers have debated for centuries over the peaceful or aggressive nature of humans. This talk will present work from psychology, anthropology and animal behaviour to critically evaluate the extent to which our evolutionary past explains our aggressive or peaceful tendencies.

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Maths & Physics Students Publish An Article On Exoring & Exomoons

Congratulations to current Mathematics student (Brayden Albery) and Physics alumni (Jake Muff) on their first research article. Both worked on small research projects during the summer, one of which was funded by Undergraduate Research Opportunity Scheme (UROS), to help understand the huge ring system thought to orbit the large exoplanet known as J1407b. The ring system was inferred by the unusually long and uneven transit when the planet passed in front of the star J1407, also known as V1400 Centauri. Previous work had shown that a gap in the ring could not be caused by an orbital resonance with a nearby exomoon, similar to how the Cassini Division is formed by the 2:1 orbital resonance with the moon Mimas (seen as the gap in the middle of the ring below).

The new research aim tot investigate if exomoons were able to form in the ring, which could then carve out a gap and is comparable to how the moons Pan and Daphne carve gaps in Saturn’s rings (below).

Simulations of the ring around J1407b as it orbited the star on a very elliptical orbit showed that it was not possible to form moons. The ring underwent significant disruption that hindered the formation of moons. However, an interesting feature was observed in one of the models. A gap did form in a similar location (0.4AU) in the ring where the original gap had been inferred from the transit.

Above: Four models of a retrograde ring system during their close encounter with the star. The eccentricity of the planets orbit increases for each row, and shows a greater degree of distortion. The right hand side gives the surface density of the ring.

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