Tag: ETH Zürich

Madagascar’s tilted past: How two ancient rifts sculpted a living island

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Madagascar’s cliffs, rolling plateaus, and winding rivers weren’t shaped by a single violent event. Instead, the island’s breathtaking landscape took form through two massive tectonic rifts that happened tens of millions of years apart.

These shifts tilted the land, redirected rivers, and sculpted the island’s dramatic shape — steep cliffs dropping into the Indian Ocean on the east and gentle plains stretching toward the Mozambique Channel on the west. Together, these forces created not only a striking landscape but also one of the most biologically rich ecosystems on Earth.

Two Ancient Rifts, One Remarkable Island

Long before Madagascar stood alone in the ocean, it was part of the ancient supercontinent Gondwana. About 170 million years ago, the first big tectonic break separated it from Africa. The crust folded upward, forming a massive western escarpment, and rivers flowed east toward the Indian Ocean, cutting deep valleys into a rising plateau.

The escarpment mountains of western Madagascar. The landscape is dominated by isolated remnant peaks, witnesses of an ancient plateau that has been deeply incised by large river systems over millions of years. (CREDIT: Romano Clementucci / ETH Zurich)

Roughly 80 million years later, another rift opened — this time between Madagascar, India, and the Seychelles. The island tilted again, but in the opposite direction. Land that once sloped east began to dip west, reversing river flow and shifting the island’s main watershed toward the east. The towering western escarpment eroded into scattered highlands, while a new, steep cliff line rose along the eastern coast.

“The water divide is the key to the geography of Madagascar,” said Romano Clementucci, a geologist at ETH Zurich and lead author of the new Science Advances study. “Each time the island tilted, the line separating rivers flowing east or west jumped across the island, changing how water and erosion shaped the land.”

Rivers That Redraw the Land

These tilts didn’t just bend river paths — they rebuilt the island’s surface. Old riverbeds were abandoned, new valleys were carved, and some rivers even reversed course. The result is striking: steep cliffs and fast rivers in the east, soft slopes and wide plains in the west.

Using high-resolution satellite imagery, erosion data, and computer models, Clementucci’s team mapped Madagascar’s slow transformation in remarkable detail. They used cosmogenic isotopes like beryllium-10 (^10Be), which build up in rocks exposed to cosmic rays, to measure how quickly erosion reshaped the island over millions of years.

The escarpment mountains of eastern Madagascar, shaped by a tropical climate and steep topography. The escarpment has been retreating inland since the second rifting event (90 Ma) and today acts as a natural barrier to rainfall, marking the western limit of the island’s humid eastern rainforests. (CREDIT: Romano Clementucci / ETH Zurich)

Their results show erosion remains most intense along the eastern escarpment. In the south, cliffs retreat about 170 meters per million years. But in the north — a more tectonically active area — the pace quickens to nearly 3,800 meters per million years. By comparison, the central plateau erodes slowly, only about seven meters per million years, preserving remnants of Madagascar’s ancient surface.

Re-Creating an Island in Motion

To confirm their findings, researchers ran computer simulations of Madagascar’s geologic past. Each rifting event caused one side of the island to sink, creating a new escarpment that gradually eroded inward. During the second rift, the tilt reversed, and the entire landscape reshaped again.

The model successfully recreated Madagascar’s modern features — the sharp eastern escarpment, the gentle western slope, and the “knickpoints,” or sudden drops in river elevation, seen today. These knickpoints are relics of ancient changes in the island’s drainage system.

And the story isn’t over. Volcanic and tectonic forces continue to reshape Madagascar today, especially in regions like the Ankaratra volcanic field and the Alaotra–Ankay Graben. These active zones still alter river courses, sink parts of the plateau, and produce mild earthquakes — signs that the island’s crust is far from quiet.

Morphostructural features of Madagascar and topographic escarpments. (CREDIT: Science Advances)

A Landscape That Gave Rise to Life

Madagascar’s incredible biodiversity — from lemurs and chameleons to baobabs — has long been credited to isolation and climate. Clementucci’s study adds another key factor: geology.

The team found a strong link between erosion rates and plant diversity along the eastern escarpment. Where slopes are steeper and rivers shift more often, plant species multiply — from roughly 1,200 in the south to more than 2,000 in the north. Rainfall alone can’t explain the difference. Instead, the land’s constant reshaping seems to have fragmented habitats and pushed species to evolve separately.

In essence, Madagascar’s shifting terrain acted like a “speciation pump.” When rivers changed course or valleys deepened, populations became isolated and began to evolve on their own. That process helped produce the island’s astonishing biodiversity — where more than 90% of mammals and reptiles and over 80% of plants exist nowhere else on Earth.

“Our research shows that ancient tectonic forces rejuvenated Madagascar’s surface,” Clementucci said. “By tilting the island and shifting its main rivers and mountains, these forces created fragmented environments where species evolved in isolation — especially along the island’s striking eastern escarpment.”

Channel steepness (ksn), normalized distance (χ) map, and linear geomorphic features defining remnant escarpments on plateau edges in central and northern Madagascar. (CREDIT: Science Advances)

Lessons From a “Quiet” Continent

Madagascar’s story challenges the assumption that so-called “passive” continental margins — like those in Brazil, South Africa, or Australia — are geologically stable. Even after rifting ends, slow but steady movements can keep reshaping landscapes and influencing ecosystems.

This understanding may also explain why other “ancient” islands host so much biodiversity. Even subtle geological shifts, spread over millions of years, can shape how species form, adapt, and survive.

Why It Matters

By linking geology and biodiversity, this study shows how deeply life is tied to a changing Earth. The living and non-living parts of our planet evolve together — one shaping the other over time.

For conservationists, the findings emphasize protecting entire landscapes, not just isolated habitats. The same tectonic and erosional forces that once created diversity could, if disrupted, permanently fracture ecosystems.

As Madagascar continues to move and wear away, it stands as living proof that the Earth is never truly still — it tilts, breathes, and builds life in the process.

Research findings are available online in the journal Science Advances.

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October 25, 2025
Soil microbes speed up CO2 emissions amid global warming

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Newswise — The rise in atmospheric carbon dioxide (CO₂) concentration is a primary catalyst for global warming, and an estimated one fifth of the atmospheric CO₂ originates from soil sources. This is partially attributed to the activity of microorganisms, including bacteria, fungi, and other microorganisms that decompose organic matter in the soil utilizing oxygen, such as deceased plant materials. During this process, CO₂ is released into the atmosphere. Scientists refer to it as heterotrophic soil respiration.

Based on a recent study published in the scientific journal Nature Communications, a team of researchers from ETH Zurich, the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, the Swiss Federal Institute of Aquatic Science and Technology Eawag, and the University of Lausanne has reached a significant conclusion. Their study indicates that emissions of CO₂ by soil microbes into the Earth’s atmosphere are not only expected to increase but also accelerate on a global scale by the end of this century.

Using a projection, they find that by 2100, CO₂ emissions from soil microbes will escalate, potentially reaching an increase of up to about forty percent globally, compared to the current levels, under the worst-case climate scenario. “Thus, the projected rise in microbial CO₂ emissions will further contribute to the aggravation of global warming, emphasising the urgent need to get more accurate estimates of the heterotrophic respiration rates,” says Alon Nissan, the main author of the study and an ETH Postdoctoral Fellow at the ETH Zurich Institute of Environmental Engineering.

Soil moisture and temperature as key factors

These findings do not only confirm earlier studies but also provide more precise insights into the mechanisms and magnitude of heterotrophic soil respiration across different climatic zones. In contrast to other models that rely on numerous parameters, the novel mathematical model, developed by Alon Nissan, simplifies the estimation process by utilising only two crucial environmental factors: soil moisture and soil temperature.

The model represents a significant advancement as it encompasses all biophysically relevant levels, ranging from the micro-scales of soil structure and soil water distribution to plant communities like forests, entire ecosystems, climatic zones, and even the global scale. Peter Molnar, a professor at the ETH Institute of Environmental Engineering, highlights the significance of this theoretical model which complements large Earth System models, stating, “The model allows for a more straightforward estimation of microbial respiration rates based on soil moisture and soil temperature. Moreover, it enhances our understanding of how heterotrophic respiration in diverse climate regions contributes to global warming.”

Polar CO₂ emissions likely to more than double

A key finding of the research collaboration led by Peter Molnar and Alon Nissan is that the increase in microbial CO₂ emissions varies across climate zones. In cold polar regions, the foremost contributor to the increase is the decline in soil moisture rather than a significant rise in temperature, unlike in hot and temperate zones. Alon Nissan highlights the sensitivity of cold zones, stating, “Even a slight change in water content can lead to a substantial alteration in the respiration rate in the polar regions.”

Based on their calculations, under the worst-case climate scenario, microbial CO₂ emissions in polar regions are projected to rise by ten percent per decade by 2100, twice the rate anticipated for the rest of the world. This disparity can be attributed to the optimal conditions for heterotrophic respiration, which occur when soils are in a semi-saturated state, i.e. neither too dry nor too wet. These conditions prevail during soil thawing in polar regions.

On the other hand, soils in other climate zones, which are already relatively drier and prone to further desiccation, exhibit a comparatively smaller increase in microbial CO₂ emissions. However, irrespective of the climate zone, the influence of temperature remains consistent: as soil temperature rises, so does the emission of microbial CO₂.

How much CO₂ emissions will increase by each climate zone

As of 2021, most CO₂ emissions from soil microbes are primarily originating from the warm regions of the Earth. Specifically, 67 percent of these emissions come from the tropics, 23 percent from the subtropics, 10 percent from the temperate zones, and a mere 0.1 percent from the arctic or polar regions.

Significantly, the researchers anticipate substantial growth in microbial CO₂ emissions across all these regions compared to the levels observed in 2021. By the year 2100, their projections indicate an increase of 119 percent in the polar regions, 38 percent in the tropics, 40 percent in the subtropics, and 48 percent in the temperate zones.

Will soils be a CO₂ sink or a CO₂ source for the atmosphere?

The carbon balance in soils, determining whether soils act as a carbon source or sink, hinges on the interplay between two crucial processes: photosynthesis, whereby plants assimilate CO₂, and respiration, which releases CO₂. Therefore, studying microbial CO₂ emissions is essential for comprehending whether soils will store or release CO₂ in the future.

“Due to climate change, the magnitude of these carbon fluxes—both the inflow through photosynthesis and the outflow through respiration—remains uncertain. However, this magnitude will impact the current role of soils as carbon sinks,” explains Alon Nissan.

In their ongoing study, the researchers have primarily focused on heterotrophic respiration. However, they have not yet investigated the CO₂ emissions that plants release through autotrophic respiration. Further exploration of these factors will provide a more comprehensive understanding of the carbon dynamics within soil ecosystems.

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June 23, 2023
A dual boost for optical delay scanning

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Newswise — Ultrafast laser technology has enabled a trove of methods for precision measurements. These include in particular a broad class of pulsed-laser experiments in which a sample is excited and, after a variable amount of time, the response is measured. In such studies, the delay between the two pulses should typically cover the range from femtoseconds to nanoseconds. In practice, scanning the delay time over a range that broad in a repeatable and precise manner is a significant challenge. A team of researchers in the group of Prof. Ursula Keller in the Department of Physics at ETH Zurich, with main contributions from Dr. Justinas Pupeikis, Dr. Benjamin Willenberg and Dr. Christopher Phillips, has now taken a major step towards a solution that has the potential to be a game changer for a wide range of practical applications. Writing in Optica, they recently introduced and demonstrated a versatile laser design that offers both outstanding specifications and a low-complexity setup that runs stably over many hours.

The long path to long delays

The conceptually simplest solution to scanning optical delays is based on a laser whose output is split into two pulses. While one of them takes a fixed route to the target, the optical path for the second pulse is varied with linearly displacing mirrors. The longer the path between mirrors, the later the laser pulse arrives at the target and the longer is the delay relative to the first pulse. The problem, however, is that light travels at famously high speed, covering some 0.3 metres per nanosecond (in air). For mechanical delay lines this means that scanning to delays up to several nanoseconds requires large devices with intricate and typically slow mechanical constructions.

An elegant way to avoid complex constructions of that kind is to use a pair of ultrashort pulse lasers that emit trains of pulses, each at slightly different repetition rates. If, say, the first pulses emerging from each of the lasers are perfectly synchronized, then the second pair has a delay between the pulses that corresponds to the difference in repetition times of the two lasers. The next pair of pulses has twice that delay between them, and so on. In this manner, a perfectly linear and fast scan of optical delays without moving parts is possible — at least in theory. The most refined type of a laser system generating two such pulse trains is known as a dual comb, in reference to the spectral structure of the output consisting of a pair of optical frequency combs.

Whereas the promise of the dual-comb approach has long been clear, progress towards applications was hindered by challenges related to designing a readily deployable laser system that provides two simultaneously operating combs of the required quality and with high relative stability. Now, Pupeikis et al. made a breakthrough towards such a practical laser, and the key is a new way to generate the two frequency combs in one and the same laser cavity.

Two from one

The task the researchers had at hand was to construct a laser source that consist of two coherent optical pulse trains that are basically identical in all properties except from that all-important difference in repetition rate. A natural route to achieve this is to create the two combs in the same laser cavity. Various approaches for realizing such laser-cavity multiplexing have been introduced in the past. But these typically require that additional components are placed inside the cavity. This introduces losses and different dispersion characteristics for the two combs, among other issues. The ETH physicists have overcome these issues while still ensuring that the two combs share all of the components inside the cavity.

They achieved this by inserting into the cavity a ‘biprism’, a device with two separate angles on the surface from which light is reflected. The biprism splits the cavity mode into two parts, and the researchers show that by suitable design of the optical cavity the two combs can be spatially separated on the active intracavity components while still taking a very similar path otherwise. ‘Active components’ refers here to the gain medium, where lasing is induced, and to the so-called SESAM (semiconductor saturable absorber mirror) element, which enables mode-locking and pulse generation. The spatial separation of the modes at these stages means that two combs with distinct spacing can be generated, while most other properties are essentially duplicated. In particular, the two combs have highly correlated timing noise. That is, while imperfections in the temporal comb structure are unavoidably present, they are almost the same for the two combs, making it possible to deal with such noise.

A gate to practical applications

An outstanding feature of the novel single-cavity architecture now introduced is that it does not require compromises in laser design. Instead, cavity architectures that are optimal for single-comb operation can be readily adapted for dual-comb use. With that, the new design also represents a major simplification relative to commercial products and opens up a path for the production and deployment of this new class of ultrafast laser sources.

The benchmarks achieved in the first demonstrations are highly encouraging. The researchers scanned an optical delay of 12.5 ns (equivalent to a distance of 3.75 m in air) with 2-fs precision (which is less than a micrometre in physical distance) at rates of up to 500 Hz and with record-high stability for a single-cavity dual-comb laser. The obtained performance — including the high power of more than 2.4 W for each comb, the short pulse durations of less than 140 fs, and the demonstrated coupling to an optical parametric oscillator (OPO) for converting the light into a different wavelength regime — underline the practical potential of the approach for a wide spectrum of measurements, from precision optical ranging (the optical measurement of absolute distance) to high-resolution absorption spectroscopy and nonlinear spectroscopy for sampling ultrafast phenomena.

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ETH Zurich

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November 10, 2022
Mapping human brain development

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Newswise — The human brain is probably the most complex organ in the entire living world and has long been an object of fascination for researchers. However, studying the brain, and especially the genes and molecular switches that regulate and direct its development, is no easy task.

To date, scientists have proceeded using animal models, primarily mice, but their findings cannot be transferred directly to humans. A mouse’s brain is structured differently and lacks the furrowed surface typical of the human brain. Cell cultures have thus far been of limited value in this field, as cells tend to spread over a large area when grown on a culture dish; this does not correspond to the natural three-dimensional structure of the brain.

Mapping molecular fingerprints

A group of researchers led by Barbara Treutlein, ETH Professor at the Department of Biosystems Science and Engineering in Basel, has now taken a new approach to studying the development of the human brain: they are growing and using organoids – millimetre-sized three-dimensional tissues that can be grown from what are known as pluripotent stem cells.

Provided these stem cells receive the right stimulus, researchers can program them to become any kind of cell present in the body, including neurons. When the stem cells are aggregated into a small ball of tissue and then exposed to the appropriate stimulus, they can even self-organise and form a three-dimensional brain organoid with a complex tissue architecture.

In a new study just published in Nature, Treutlein and her colleagues have now studied thousands of individual cells within a brain organoid at various points in time and in great detail. Their goal was to characterise the cells in molecular-genetic terms: in other words, the totality of all gene transcripts (transcriptome) as a measure of gene expression, but also the accessibility of the genome as a measure of regulatory activity. They have managed to represent this data as a kind of map showing the molecular fingerprint of each cell within the organoid.

However, this procedure generates immense data sets: each cell in the organoid has 20,000 genes, and each organoid in turn consists of many thousands of cells. “This results in a gigantic matrix, and the only way we can solve it is with the help of suitable programs and machine learning,” explains Jonas Fleck, a doctoral student in Treutlein’s group and one of the study’s co-lead authors. To analyse all this data and predict gene regulation mechanisms, the researchers developed their own program. “We can use it to generate an entire interaction network for each individual gene and predict what will happen in real cells when that gene fails,” Fleck says.

Identifying genetic switches

The aim of this study was to systematically identify those genetic switches that have a significant impact on the development of neurons in the different regions of brain organoids.

With the help of a CRISPR-Cas9 system, the ETH researchers selectively switched off one gene in each cell, altogether about two dozen genes simultaneously in the entire organoid. This enabled them to find out what role the respective genes played in the development of the brain organoid.

“This technique can be used to screen genes involved in disease. In addition, we can look at the effect these genes have on how different cells within the organoid develop,” explains Sophie Jansen, also a doctoral student in Treutlein’s group and the second co-lead author of the study.

Checking pattern formation in the forebrain

To test their theory, the researchers chose the GLI3 gene as an example. This gene is the blueprint for the transcription factor of the same name, a protein that docks onto certain sites on DNA in order to regulate another gene. When GLI3 is switched off, the cellular machinery is prevented from reading this gene and transcribing it into an RNA molecule.

In mice, mutations in the GLI3 gene can lead to malformations in the central nervous system. Its role in human neuronal development was previously unexplored, but it is known that mutations in the gene lead to diseases such as Greig cephalopolysyndactyly and Pallister Hall Syndromes.

Silencing this GLI3 gene enabled the researchers both to verify their theoretical predictions and to determine directly in the cell culture how the loss of this gene affected the brain organoid’s further development. “We have shown for the first time that the GLI3 gene is involved in the formation of forebrain patterns in humans. This had previously been shown only in mice,” Treutlein says.

Model systems reflect developmental biology

“The exciting thing about this research is that it lets you use genome-wide data from so many individual cells to postulate what roles individual genes play,” she explains. “What’s equally exciting in my opinion is that these model systems made in a Petri dish really do reflect developmental biology as we know it from mice.”

Treutlein also finds it fascinating how the culture medium can give rise to self-organised tissue with structures comparable to those of the human brain – not only at the morphological level but also (as the researchers have shown in their latest study) at the level of gene regulation and pattern formation. “Organoids like this are truly an excellent way to study human developmental biology,” she points out.

Versatile brain organoids

Research on organoids made up of human cell material has the advantage that the findings are transferable to humans. They can be used to study not only basic developmental biology but also the role of genes in diseases or developmental brain disorders. For example, Treutlein and her colleagues are working with organoids of this type to investigate the genetic cause of autism and of heterotopia; in the latter, neurons appear outside their usual anatomical location in the cerebral cortex.

Organoids may also be used for testing drugs, and possibly for culturing transplantable organs or organ parts. Treutlein confirms that the pharmaceutical industry is very interested in these cell cultures.

However, growing organoids takes both time and effort. Moreover, each clump of cells develops individually rather than in a standardised way. That is why Treutlein and her team are working to improve the organoids and automate their manufacturing process.

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October 7, 2022