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Northwest Africa, 24 Million years ago.
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To anyone familiar with Africa today, its extensive grasslands and savannahs can seem almost timeless: landscapes of grasses, scattered trees, grazing herbivores, predators and recurrent fires. But, like every modern ecosystem, the African savannah has a history. It was not created fully formed, stocked with its present collection of plants and animals, during a mythical creation week a few thousand years ago. It developed through a succession of environmental and evolutionary changes extending over tens of millions of years.
Some of that history is preserved not on the African continent itself, where erosion and geological disturbance have left gaps in the terrestrial record, but beneath the neighbouring Atlantic Ocean. Plant waxes blown from the land settled on the sea surface and were incorporated into sediments accumulating slowly on the ocean floor. Layer upon layer, these sediments preserved a chemical record of the vegetation growing in north-west Africa at different times.
Now, Anna K. Schartman, Pratigya J. Polissar and Caroline A. E. Strömberg have used these molecular fossils and their carbon-isotope composition to reconstruct some 24 million years of ecological change. Their findings are reported in an open-access paper, “The origin and development of the Miocene northwest African savanna”, published in the Proceedings of the National Academy of Sciences.
The researchers found that the region’s closed forests and woodlands began giving way to a much more open ecosystem about 15–14 million years ago—approximately five million years earlier than earlier regional reconstructions had suggested. This first open landscape was not equivalent to the modern African savannah. It was rich in C3 grasses and had no close modern counterpart. The familiar C4-grass savannah developed later and in stages, with its most rapid expansion occurring between about 7.4 and 6.4 million years ago.
This does not conflict with research publicised by UC Santa Cruz in 2023, which found locally abundant C4 grasses in parts of eastern Africa between about 21 and 16 million years ago. That earlier research examined terrestrial fossil sites in Kenya and Uganda; the new study reconstructs regional vegetation in north-west Africa from wind-blown plant waxes preserved in marine sediments. Together, the studies show that Africa did not undergo a single, continent-wide transformation. Different mixtures of forest, woodland and grassland appeared in different regions at different times.
Glossary^ Reconstructing Ancient African Grasslands. C3 plants. Plants in which the first stable product of carbon fixation contains three carbon atoms. Carbon dioxide is captured directly by the enzyme RuBisCO through the Calvin cycle. Most trees and shrubs, together with many grasses and crops such as wheat and rice, use C3 photosynthesis. It generally performs well under cool or moist conditions and when atmospheric carbon dioxide is relatively abundant, but becomes less efficient in hot, dry conditions because of increased photorespiration.Nor was the modern savannah produced by one simple climatic switch. Its development accompanied periods of global cooling and increasing aridity, but the authors identify a nonlinear interaction involving climate, the characteristics of C3 and C4 plants, wildfire and grazing animals. Once grasses began spreading, fire and herbivory could help to suppress tree cover, reinforcing the expansion of open habitats. The ecosystem was assembled through changing feedbacks among organisms and their environment—not imposed upon the world in its finished form.
C4 plants. Plants that initially fix carbon dioxide into a four-carbon compound using the enzyme PEP carboxylase. The carbon is then delivered to specialised cells where carbon dioxide is concentrated around RuBisCO. This carbon-concentrating mechanism requires additional energy but greatly reduces photorespiration and usually improves water-use efficiency. It gives C4 plants an advantage under high temperatures, strong sunlight, seasonal water stress and relatively low atmospheric carbon dioxide. Many tropical and subtropical grasses—including maize, millet, sorghum and sugar cane—use this pathway.
Why the distinction matters. Modern African savannahs commonly combine C4 grasses with C3 trees and shrubs. However, the earliest open ecosystem identified in the new study was rich in C3 grasses. Its vegetation therefore differed substantially from that of most modern tropical African savannahs and has been described as having no close modern analogue.
Photorespiration. A wasteful reaction in which RuBisCO binds oxygen instead of carbon dioxide. The process consumes energy and releases previously fixed carbon dioxide. It becomes more frequent under hot, dry or low-CO2 conditions. The carbon-concentrating mechanism of C4 plants largely suppresses it.
Carbon isotopes. Carbon occurs naturally in several forms, including the stable isotopes carbon-12 and carbon-13. C3 and C4 plants discriminate differently between them during photosynthesis, producing characteristically different carbon-isotope ratios. Those differences can remain detectable in ancient plant waxes, allowing researchers to estimate the changing contributions of C3 and C4 vegetation.
δ13C (“delta carbon-13”). The conventional measurement of the ratio of carbon-13 to carbon-12 in a sample, expressed relative to an agreed standard. C3 plants discriminate more strongly against carbon-13 and therefore generally have more negative δ13C values than C4 plants. Researchers must also allow for such influences as aridity, changes in atmospheric carbon and mixtures of material from different sources.
Plant-wax biomarkers. Durable organic compounds produced in the waxy coatings of leaves. Long-chain hydrocarbons known as n-alkanes are particularly resistant to degradation. After leaves decay, these molecules can be carried by rivers or wind into lakes and oceans, where some become buried and preserved in sediment.
Molecular fossil. A recognisable molecule or chemical signature derived from a formerly living organism and preserved in sediment or rock. Unlike a conventional fossil, it need not retain the visible shape of the organism. Plant-wax molecules are molecular fossils that can reveal past vegetation even where leaves, pollen and other recognisable plant remains are scarce.
Palaeoecological proxy. A measurable feature used to infer an environmental condition that cannot be observed directly. Plant-wax carbon isotopes are proxies for vegetation type; other proxies can provide evidence about temperature, rainfall, fire or dust deposition. Conclusions become stronger when several independent proxies agree.
Marine sediment core. A cylindrical sample drilled from sediments beneath the sea floor. Except where the layers have been disturbed, deeper sediments are older than those above them. Their ages can be reconstructed using several independent methods, creating a chronological archive of environmental change. The cores analysed in this study preserve plant material blown from north-west Africa into the Atlantic over approximately 24 million years.
Savannah. An open ecosystem dominated by grasses but containing varying amounts of trees and shrubs. Savannahs form a continuum from almost treeless grassland to relatively densely wooded grassland; they are not all ecologically or botanically identical.
No modern analogue. An ancient ecosystem whose particular combination of vegetation, climate and ecological structure has no close equivalent today. It does not mean that all its component species were unique, but that their association and relative abundance differed from those found in modern ecosystems.
Miocene Epoch. The geological interval extending from approximately 23 million to 5.3 million years ago. It witnessed major climatic changes and the expansion and diversification of many modern plant and mammal groups.
Ecological feedback. A process in which an environmental change reinforces or modifies itself. For example, expanding grass cover can provide more fuel for fire; repeated fires can suppress young trees and maintain open grassland. Grazing animals, vegetation, rainfall and fire can therefore interact rather than acting as separate, independent causes.
For creationists, the evidence presents the familiar chronological problem. The molecular remains occur in an ordered sequence through marine sediments spanning 24 million years, recording forests, an unfamiliar C3-grass-dominated savannah and the later expansion of C4 grasslands. Such a succession cannot sensibly be compressed into a few thousand years or explained as debris deposited indiscriminately during a single recent global flood. Instead, it records a changing planet on which climates, vegetation and animal communities evolved together over geological time.
The paper in PNAS was accompanied by a press release via EurekAlert!
African grasslands became widespread over five million years earlier than previously known
The iconic grassland savannas of Africa are geographically extensive and important for both local fauna and how they affect global climate. But where did they come from, and how will they change in the future? Ongoing warming, rising CO2 levels, and shifting rainfall patterns are likely to profoundly change these ecosystems. These effects are difficult to predict because they can alter these ecosystems in competing ways.
This study investigates the transformation of Northwest African ecosystems over the past 24 million years using molecular fossils and their isotopic chemistry to understand their history and allow projections for the future. The molecular fossils are blown from the continent to the ocean where they can be preserved in ocean sediments. The research team sampled drillcores from the International Ocean Discovery Program and extracted and measured these fossils to understand when grasslands developed, and the possible causes for their rise to prominence over time.
Map of study area showing the major ecosystem divisions in the modern day summarized from Sayre et al. The dark red circles mark the locations of the core sites (ODP 659 and DSDP 368) investigated in this study.Credit: Schartman, et. al. (2026)
They found that the first open (grassland) ecosystems occurred approximately 15 million years ago, or about 5 million years earlier than previously thought. This ecosystem was different from today’s in the types of grasses present, and it was not until millions of years later that grasslands more similar to our modern savanna became dominant.
The emergence of African grasslands is a hallmark event in global climate and ecosystem change. The development of grassland ecosystems at 15 million years also set the stage for faunal evolution in Africa that includes our human ancestors. The establishment at 15 million years ago and subsequent transformation occurred during periods of global cooling and aridification, but involved complex interactions between climate, wildfire, and herbivores that still operate today. The geologic record indicates that the response of savannas and other subtropical open ecosystems to future climate perturbations will depend on the nature and strength of these interactions, in addition to global climate changes.
This research was led by Anna Schartman during her Ph.D. at the University of California, Santa Cruz, in collaboration with her advisor, Ocean Sciences Professor Pratigya Polissar, and Professor Caroline Strömberg at the University of Washington.
Publication:
What makes this evidence especially troublesome for creationists is that it does not consist of one inconvenient fossil or a single disputed date. It is an ordered chemical history preserved through successive layers of marine sediment. The same types of durable plant-wax molecules occur throughout the cores, but their carbon-isotope signatures change systematically, recording closed woodland and forest, the appearance of an unfamiliar C3-grass-rich savannah and, millions of years later, the expansion of C4 grasslands resembling those of modern Africa.
There is no place in this sequence for the instantaneous creation of the modern African landscape. The savannah was not produced fully formed, complete with its characteristic grasses, trees, fires and grazing animals. It emerged in stages as global cooling and increasing aridity interacted with plant physiology, herbivory and fire. Nor was the process directed towards a predetermined modern ecosystem: the first open landscape was a C3-grass-dominated community with no close modern equivalent—an extinct ecological arrangement produced by the particular conditions of its time.
A single recent global flood cannot plausibly account for this record either. Such an event would need not only to deposit kilometres of marine sediment in an impossibly short time but also to arrange plant waxes into the correct chronological order, producing a coherent progression in the isotope ratios of the same classes of molecules. Simple hydraulic sorting cannot separate C3 and C4 waxes into an apparent evolutionary sequence because the distinction lies principally in their isotopic composition, not in conveniently different shapes or sizes that floodwater could sort.
The research also illustrates another contrast with creationism. Scientists had previously placed the regional opening of north-west Africa several million years later. When new evidence became available, they revised that conclusion. The still earlier C4-rich habitats found in eastern Africa do not present a contradiction but reveal a geographically varied continent on which different ecosystems developed at different times. Science accommodates that complexity because its conclusions are required to follow the evidence; creationism requires the evidence to be forced into a predetermined narrative.
Creationists can respond only by denying the dating methods, dismissing the isotope evidence or inventing an undocumented ability of a mythical flood to manufacture precisely ordered chemical histories. None of those responses constitutes a testable scientific explanation. The sediments beneath the Atlantic record what creationism says should never have existed: millions of years of ecological change, preserved layer by layer, long before the supposed “Creation Week” and the imaginary flood that was meant to have erased it all.
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