A geologist just sees the world differently. I’ve struggled to explain how and why until I stumbled on Marcia Bjornerud’s book, “Timefulness: How Thinking Like a Geologist Can Help Save the World”.
Landscapes and rocks, she suggests, hold layered memories. It has chapters, like a book waiting to be read, tools waiting to decode their untold stories. To think geologically is to see both what lies at the surface of a rock and what stories it hides. A geologist is… a romantic. They don’t just see rocks, they see the stories it hides.
That idea explains why I love the Isotope Ratio Mass Spectrometer (IRMS). It feels like one of the tools that allows us to read the faint ink in a book. But first, some history.
How the IRMS came to be
The IRMS has its roots in the 1940s. The story begins with Alfred Nier, an American physicist. In 1940 he built the first mass spectrometer specifically designed to measure the ratios of different isotopes of the same element with high precision. His instrument could detect, for example, the difference between carbon-12 and carbon-13 — atoms of the same element, but with slightly different masses.
The breakthrough moment for the IRMS really took hold in the 1950s by Harold Urey. Urey, who had already won the Nobel Prize for discovering deuterium, showed that the ratio of oxygen isotopes (O-16 vs O-18) preserved in ancient shells and rocks changes with temperature. In other words, isotope ratios are a record of past climate. That turned IRMS from a physics instrument into an earth sciences tool overnight.
From there the field exploded. By the 1970s and 80s, the IRMS was being used to trace carbon cycles, distinguish biological from geological carbon sources, date archaeological samples, and crucially, for what we do at Alt Carbon — measure whether carbon in the soil is coming from weathering reactions, or biological processes.
When we run tests for Enhanced Rock Weathering, we need to prove that the carbon being sequestered is genuinely coming from rock dissolution, not from organic matter decomposition, or some other source. The IRMS lets you read the isotopic signature of that carbon and trace it back to its origin. It's essentially a fingerprinting tool for carbon.
Researching for my thesis
The IRMS became real to me during my Masters research. I worked on stalagmites from the Mauritian Archipelago with my mentor and advisor, Dr. Voary’s lab group, using the lab at the University of Houston. Stalagmites are carbonate formations that grow slowly, layer by layer, from cave drip water, each band locking in the isotopic signature of the water from which it precipitated. In effect, they function as natural climate archives.
By measuring oxygen and carbon isotopes using the IRMS, I could read those layers and reconstruct hydroclimatic variability in the Indian Ocean reaching back to ~23,000 years before present!
Oxygen isotopes traced shifts in rainfall balance and moisture pathways linked to atmospheric circulation over the Indian Ocean, while carbon isotopes reflected vegetation density, soil respiration, and ecological processes occurring above the cave.
What emerged from this study formed the bulk of my work. I was able to see a notable shift in regional climate during the Last Ice Age, often referred to as LGM (Last Glacial Maxima) in the scientific community. Evidence suggests that the equatorial rain belt over the southwestern Indian Ocean, which is intensely wet today, had massive arid spells. This pattern appears consistent with signals from other regional climate archives across East Africa and Madagascar. Broader comparison of regional climatic records also show alignment with large-scale climate variability recorded in Greenland and Antarctic ice cores.
The IRMS is remarkably good at translating subtle differences in isotope ratios into a coherent timeline of environmental change. Once stalagmite layers are dated, the isotopic signals become anchored in time, turning a mineral column into a history book.
The interval we captured in our stalagmite overlaps with the *late Pleistocene, when modern humans were spreading across continents and adapting to shifting climates. The timeframe also sits within the broader biological backdrop often called the “Reign of Mammals” — when you and I came to be. Through the isotopic language preserved in those cave layers, the IRMS provides a bridge between the wider timeline of life, placing regional environmental change within a story that stretches across the chapters of evolution of life.
*The Late Pleistocene is roughly between 130,000 and 12,000 years ago. It's the era of woolly mammoths, early humans, and the last great ice ages, ending with the world warming into the climate we live in today.
How incredible is it that the signals recorded in a cave echo those preserved in distant lakes and polar ice caps like a deeply connected system; making it seem like the Earth is conscious and alive?!!
A 23,000-year-old history from a droplet
What fascinates me is how far this idea travels beyond geology. The same IRMS that reads cave deposits is used to detect synthetic hormones in sports doping. It can distinguish between real honey and its dilution with sugar syrup, whether whisky truly aged where it claims, or whether a banned substance entered an athlete’s body naturally or artificially. Across fields that rarely intersect, the principle remains unchanged: isotopes carry origin stories.
And perhaps that is why the IRMS stays with me. It reminds you that matter remembers. Whether in a stalagmite, a drop of rain, a bottle of wine, or a strand of hair, tiny differences in mass preserve traces of journeys already taken.
I have to admit, human ingenuity is also an equally incredible thing. Take a pause to realise the kind of ingenuity we have exhibited in the creation of these machones; how advanced we have gotten in reading these subtle signals. The world is layered with memory, and with the right lens, even the smallest signals can speak across time. If that’s not romance in motion, I can't imagine what is.
P.S. In my next post, I will talk about how I used the IRMS to understand rains during the Last Ice Age.