Dust in the wind: how broken crystal surfaces help shape clouds, climate and life

Crystal edges are like broken Lego constructions. Where pieces have broken off, new building blocks can attach, allowing new things to take shape. The same happens at the edges of crystals. These tiny reaction surfaces can act as 'seeds' for some of the most fundamental processes that have shaped our planet as we know it. They contribute to how Earth looks from space, how life formed, and how engineers aim to interact with climate.

By Kathelijne Bonne. Support GondwanaTalks through a one-time or recurring donation through this easy way.

One intriguing snippet of knowledge is that raindrops do not simply appear out of nowhere. Every individual drop needs a 'seed', a tiny particle around which water vapour can condense to form a droplet or ice crystal. This little fact has vast consequences, because from droplets, clouds are born.

The white and blue marbled appearance of Earth seen from space is due to minerals and crystals

The bright white cloud masses that give our planet its marbled blue appearance reflect sunlight. The more radiation is reflected back into space, the less the planet warms. In this way, clouds form part of the natural system that protect and insulate the planet's surface. It has kept the climate relatively stable, which helped life to persist on Earth for billions of years. 

Next to clouds, water vapour, oxygen and nitrogen, the atmosphere is loaded with tiny dust particles that enter our lungs with every breath. These particles swirl around the planet in aerosols, permeating our environment and our cells. Many of these airborne particles act as the seeds or 'condensation nuclei' that play an essential role in the formation of clouds and rain.

How is dust created and lifted into the atmosphere to form aerosols? 

Much of the mineral dust in natural aerosols comes from sediment loosened from the Earth's crust through weathering and soil formation. Soil is the interface between solid rock, life, atmosphere and water. Weathering breaks down rock into particles of different sizes, such as sand, silt and clay, made up of many different minerals. The finer the particles, the more easily they are picked up by the wind.

Volcanoes also contribute substantially to atmospheric particles, sometimes enough for a single eruption to affect the climate. Pollen, spores, viruses, organic matter and sea salt can also be carried in aerosols. Winds and atmospheric currents transport these particles over great distances, sometimes around the globe.

But the most obvious sources of dust are deserts. The Sahara, for example, produces immense quantities of mineral dust that blow across the Atlantic. Remarkably, the seemingly lifeless Sahara fertilises both the ocean and the Amazon rainforest (or what is left of it) with natural nutrients such as iron.

Foam from waves whipped up by wind and storms gives rise to sea spray rich in salt and organic matter from marine life. In low-lying Belgium and the Netherlands, and along coastlines elsewhere, clouds often form around these sea-salt particles.

Tiny dust particles can act as 'condensation nuclei' when they have the size of a scale of a butterfly's wings or smaller

Among airborne particles, fine dust—including particles smaller than two microns, roughly the thickness of a butterfly's wing scale—can act effectively as condensation nuclei, the starting points around which water droplets gather and clouds form.

Creating rain through stratospheric aerosol injection: are we already deliberately interfering with climate?  

There is an abundance of natural particles capable of seeding clouds, but humans too stir up dust in many ways—most notably through pollution, such as smoke and soot, and by intensifying soil erosion, as happened during the Dust Bowl. 

Yet injecting particles into the atmosphere or stratosphere in a controlled way—in the form of aerosols to mitigate climate impacts—is a very old dream. Its feasability, side effects and the ethics that surround it have been intensely debated. Today, with planetary boundaries being surpassed, an 'intervention' becomes a more likely idea.

Stratospheric aerosol injection could theoretically slow global warming. On more local scales, cloud-seeding experiments have already produced measurable effects in some circumstances, although the technique is far from a silver bullet.

The drought-prone southwestern United States experimented with aerosols, with modest success. Scientists have tried to stimulate snowfall and rainfall since the 1960s in the Sierra Nevada, to increase meltwater for farming. The technique is far from miraculous: moisture and the right type of cloud must already be present for it to work. 

For creating rain or snow, silver iodide and dry ice (solid CO₂) worked relatively well in very high, extremely cold clouds. Salt particles on the other hand were more efficient in lower, warmer clouds. 

Are some minerals better cloud seeders than others? One type of feldspar turns out to be exceptionally efficient at creating ice crystals 

A compelling recent discovery concerns feldspar, a group of minerals found everywhere on Earth. Feldspar is abundant in igneous and metamorphic rocks and, through erosion, also in sedimentary rocks. 

One particular type of feldspar, microcline, turns out to be an exceptionally effective ice-nucleating particle. Why this particular mineral works so well has puzzled researchers for a long time. A 2023 study in Vienna revealed that the answer lies in the structure and behaviour of its crystal surfaces.

Using an atomic-force microscope, researcher Giada Franceschi and her team discovered that when feldspar surfaces break, an exposed surface appears that has many so-called 'hydroxyl groups': loose molecule ends of the crystal that act like tiny hooks or anchor points, each consisting of one oxygen (O) and one hydrogen (H) atom (chemically written as –OH). 

The hydroxyl groups attract water. Moreover, the broken microcline surfaces with these tiny hooks help water molecules arrange themselves neatly into ice, making the mineral a highly effective ice 'generator'.

Microcline is already present in atmospheric mineral dust. It is partly responsible for the way earth looks from space. Whether and how it can be used in a human-made aerosol, and whether the effect would be desireable, remains an open question.

Understanding how different aerosol particles behave adds one more small building block to the grand edifice of knowledge—a metaphor palaeontologist Richard Fortey loved to evoke—from which we hope to find ways to tackle the planetary crises of our time.

Did the geometrically repeating pattern of mineral surfaces contribute to the emergence of life?

Mineral surfaces may be small, but the questions they raise are boundless. It has led to many remarkable scientific insights, including a deeper understanding of how life may have emerged billions of years ago, after the collision with the protoplanet Theia that gave rise to the Moon.

Not only microcline but all minerals have reactive crystal surfaces. Imagine Lego again. Break a Lego house in two and there will always be protruding pieces. Similarly, exposed sites on mineral surfaces interact with their surroundings, attracting some molecules and repelling others. 

What makes mineral surfaces particularly special is the geometric, repeating patterns the atoms are arranged in. When the mineral appears in its beautifully facetted crystal form (which it doesn't always do), this atomic structure becomes visible to us in its macroscopic form.

Some of the earliest building blocks of life, floating in water, may have accumulated on mineral surfaces. There, they could have lined up, guided by the structure of the mineral's atomic arrangement. Crystal surfaces may even have acted as catalysts, making it easier for organic molecules to cluster, bind and form longer chains (polymers). 

Without these surfaces, the early formation of complex biomolecules might have been much slower or more difficult. 

Life has no mirror image. Did crystal surfaces give life its so-called chirality? A few notes on the amazing mysteries of 'handedness' and asymmetry and how they arose

The whole crystal edge and life stories lead to a phenomenon that has fascinated me ever since I got immersed in organic chemistry at university: the 'handedness', or chirality, of life. Chirality refers to the fact that two objects can be mirror images of each other without being identical in three dimensions. Objects are chiral when they cannot be superimposed on their mirror images, like our two hands.

Some of the building blocks of life—amino acids and sugars—show a striking preference for one-handedness. Their mirror-image forms exist, but living systems overwhelmingly use one orientation rather than the other.

In an extraordinary twist of fate (or unconcious decision of life?), proteins in life are built almost exclusively from 'left-handed' amino acids, while the sugars in DNA and RNA are 'right-handed'. Their mirror images have different biological properties and are not generally interchangeable in living systems. Why this asymmetry emerged is still a mystery. But there are hypotheses. One of them is that crystal surfaces may have helped give life its handedness.

There are many other crucial processes in which minerals play intriguing roles we can learn from. Whether we can alter the path we're on with climate change making use of aerosols, remains to be seen. After all, we cannot yet conjure rain in a cloudless sky, or create life from non-living matter. 

---

Explore our articles on supereruptions and how we might survive them, how the Great Plains recovered after the Dust Bowl, or dive into the supercontinent Gondwana, Snowball Earth, and how trilobites once viewed the world.

Kathelijne, editor of GondwanaTalks: I am intrigued by how earth, life, air, ocean and societies interact on geological and human timescales.

Why on earth I started GondwanaTalks.

Donation? (via Paypal or bank transfer)

An immense effort is poured into GondwanaTalks.

Are my articles somehow meaningful to you? Support my work so I can keep GondwanaTalks afloat. Your contribution makes an ultra-Plinian difference. Make a one-off or recurring donation and become a:

Stromboli Strategist
(€2/month)

Tambora Trailblazer
(€4/month)

Vesuvian Visionary
(€7/month)

Already donating? Thank you so much! Not a fan of paypal? Do a normal bank transfer.

more articles.

Do you like this post? Subscribe to the short newsletter: it is sent every couple of weeks when there is a new article, and is free of heavy files and irritating gifs.