A Hypothesis on the Extinction of Ancient Terrestrial Animals and Dinosaurs Inferred From Modern Natural Phenomena

Mass extinction events of animals have occurred multiple times in Earth's history, among which the end-Cretaceous dinosaur extinction is particularly notable. The five major extinction events span approximately 378 million years from the first through the fifth, with several smaller-scale population extinctions interspersed [1]. If the ancient environment had long been suitable for animal survival and reproduction, why did so many flourishing animal groups disappear repeatedly across different geological periods? This suggests that these extinction events were not merely accidental or isolated occurrences, but rather more likely originated from some natural disaster that recurred on geological timescales and possessed the capability of global coverage [2]. This paper proposes an alternative hypothesis derived from comprehensive reasoning based on observable modern natural phenomena [3]: naturally occurring global-scale wildfires, rather than sudden external catastrophic events, may have been the core driving factor behind the extinction of terrestrial animals and dinosaurs [4]. Examining modern natural disasters, earthquakes, floods, and typhoons all exhibit significant regional limitations; only wildfires possess the potential for unbounded spread—as long as fuel is continuously available and effective barriers are absent, the fire can expand indefinitely [5]. In the ancient period before human appearance, there were no farmlands, roads, artificial structures, or firebreaks on land, nor systematic vegetation clearance; plant cover was continuous and contiguous, lacking natural interruptions [6]. Therefore, without considering other natural phenomena, theoretically a single natural ignition point, once ignited, would expand in all directions until encountering rivers or lakes; the flames would skirt the waterbody margins, cross upstream at the headwaters, and eventually burn across the entire landmass. Animals, constrained by their limited mobility and physical endurance, could hardly escape the advancing fire front [7]. Direct burns and the drastic oxygen depletion during combustion would have caused massive immediate animal mortality; among survivors, herbivores would face food shortage due to the destruction of vegetation, and even if vegetation later regenerated, carnivores would suffer cascading extinction because of the slow recovery of herbivore populations. Whether such a fire scenario could have caused the complete extinction of terrestrial animals and dinosaurs depends primarily on the distribution density of ignition points, climatic background, and other coupled environmental factors [8]. If the Earth experienced a large-scale drought period, the hot and dry climate combined with frequent lightning could simultaneously or successively generate numerous ignition points; superimposed with atmospheric circulation and sustained high winds as fire-facilitating effects, the fire would spread rapidly [9]. Taking a single ignition point spreading at 10 m / min [10], the six-month fire radius would be approximately 2,592 km, giving a burned area of about 21.1 million km². To burn across the entire global land surface (calculated at the present land area including Antarctica, 149 million km²) within six months, about 7 non-overlapping ignition points would be required. In ancient times, with denser vegetation cover and complete absence of human interference, lightning strikes and spontaneous ignitions would have generated far more ignition points than today; over hundreds of millions of years, the probability of combined large-scale drought and frequent lightning is not low [11]. This paper further proposes that natural fire itself may have constituted the core driver of successive extinction events, without reliance on external triggers such as asteroid impacts or large-scale volcanic eruptions. In the continuously vegetated, human-free ancient terrestrial ecosystem, periodic coupling of drought and lightning would have been sufficient to spontaneously generate global firefields, directly killing terrestrial animals and triggering complete collapse of the food chain.