The kingdom of flowers was built in two brief pulses of heat.

There is a particular patience required to study the history of plants, a discipline that reads the past in pollen grains and spores, in sediments laid down millions of years before anyone thought to ask what grew there. The question that has lingered in paleobotany for decades is why flowering plants, which emerged tens of millions of years before they came to dominate, waited so long to take over. A new study published in Nature Plants suggests the answer lies in two brief intervals of extreme global warmth, moments when the planet's climate reshuffled the botanical world.

The research, led by J. M. Kale Sniderman of the University of Melbourne with colleagues from the University of Tasmania and the Natural History Museum of Vienna, analyzed more than 60,000 fossil pollen and spore records. The team applied statistical methods designed to correct for the biases inherent in the fossil record—the uneven sampling across time and region that had previously obscured the relationship between climate and plant diversity . What emerged was a pattern that had been invisible before: the highest rates of extinction and the appearance of new plant lineages were not spread evenly across time. They were concentrated in two short windows.

The first occurred during the mid-Cretaceous, roughly 100 to 84 million years ago, when ocean temperatures in what is now Australia reached extraordinary levels. The second arrived in the early Cenozoic, encompassing the Paleocene-Eocene Thermal Maximum and the Early Eocene Climatic Optimum, around 56 million years ago . It was during this second interval that flowering plants consolidated their ecological dominance, displacing gymnosperms and ferns across most terrestrial biomes. The transition was not the slow, steady advance that had been assumed. It was a jump, tied to the thermal state of the planet.

The synchrony of these turnover events across hemispheres and latitudes is what makes the finding compelling. The team compared their diversification curves with reconstructions of ocean surface temperature derived from oxygen isotopes in planktonic foraminifera. The peaks in origination and extinction aligned with the peaks in temperature, and the alignment held whether the records came from southeastern Australia, which occupied high paleolatitudes, or northeastern Africa, which sat in the tropics . A regional driver could not produce that pattern. Only a global one could.

The study also tested alternative explanations—interactions between plant groups, geographic isolation as continents drifted apart—and found that none explained the observed patterns as consistently as climate. Temperature was the dominant predictor across all analyses . The implication is stark: over geological timescales, land plant diversity is ultimately controlled by the global climate state. Warmth does not merely favor certain species. It reshapes the entire assemblage, creating opportunities for some lineages and extinguishing others.

There is a caution embedded in the research that its authors are careful to voice. The warming of the mid-Cretaceous and early Cenozoic unfolded over millions of years. The warming driven by human activity is occurring on a scale of decades. "It is likely that human-induced global warming will cause plant extinctions much faster than the extinctions that occurred during those ancient warm intervals," Chris Mays, one of the study's authors, told Infobae . The past offers a pattern, not a reassurance. The planet has reshuffled its flora before, under conditions of extreme heat. It is doing so again, and this time the heat is arriving faster than the plants can adapt.

For now, the fossil record has yielded a clearer picture of why the world became green with flowers. The answer is not a single evolutionary innovation or a competitive advantage that unfolded gradually. It is the climate itself, acting in brief and intense pulses, opening doors and closing them. The flowers that dominate the planet today owe their kingdom to moments of extraordinary warmth, and the plants of the future will owe their fate to a warmth that is arriving on a different schedule.

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Sources: Nature Plants, JoVE, Infobae