The demise of the ancient oceans occurred gradually rather than all at once.

A significant global cooling event that occurred approximately 34 million years ago did not result in a single marine extinction catastrophe, according to a new analysis. Rather, it developed as a sequence of intermittent biological disturbances throughout ocean environments.

This discovery reframes a significant change in Earth's climate as a long-term transformation of marine life rather than a sudden collapse.

Rebuilding an intricate timeline

Fossil records from 161 drill cores and rock sections show how marine animals evolved irregularly over time rather than going extinct all at once. Junxuan Fan of Nanjing University (NJU) reconstructed this worldwide sequence and found unique patterns of stability and loss that were strongly related to the locations of creatures in the ocean.

While deeper communities saw a slower and more progressive decline, surface and shallow-water species remained stable before experiencing an abrupt decline. This temporal divergence indicates that there are several overlapping environmental stresses rather than a single common cause for the change.

Different dimensions of life

The primary players were foraminifera, which are tiny, single-celled marine organisms that create shells. Their remains accumulate on the seafloor in billions. Some lived in warm shallow bottoms, some in darker sludge far below, and still others floated close to the surface.

Each group experienced the same cooling in a different way because to the significant differences in light, temperature, food, and oxygen increasing depth. The new record appears more like a prolonged rearranging than a single collapse, which can be explained by this ecological separation.

Reduce before to the freeze

Marine variety was already declining over millions of years in the late Eocene, even before Antarctica carried significant ice sheets. At first, surface-floating and shallow-bottom forms were rather stable as the overall background trend continued to decline.

During the early Priabonian, when more food appears to have reached deeper habitats, small bottom-dwellers had a brief boom. The analysis opposes the previous practice of flattening this gap into a single crisis, in part because of this early explosion.

The onset of icy conditions

Near the beginning of the Oligocene, Antarctica got its first continent-scale ice sheet, which caused the biggest break. Warm-water species were reduced by sea-surface cooling, while many bigger species' shallow habitats were constrained by declining sea levels.

According to a more comprehensive climate record, that pivotal moment occurred approximately 33.9 million years ago. Larger bottom-living and surface-floating animals quickly lost species in the fossil curve as that chilly planet gained hold.

delayed collapse from below

One of the most obvious conclusions of the record is that deep-sea ecosystems did not fall simultaneously. Deeper bottom species may have been nourished by a greater biological pump caused by carbon sinking from surface waters as oceans cooled.

Those tiny bottom-dwellers didn't go into a lengthy decline until much later, perhaps because to ongoing changes in deep-water chemistry and feeding habits. Because of this lag, the same global cooling may benefit one ecosystem temporarily before harming it in the future.

Variations in the effects of climate change

The groups aligned with various regions of the Earth system when the team compared diversity to climatic data. More attentively than deep-sea forms, surface and shallow-bottom species monitored global sea level and sea-surface temperature.

Instead, because of their darker, food-limited environment, little bottom-dwellers followed variations linked to deep-ocean temperature and carbon cycle. This division transforms an ambiguous extinction narrative into a map of who first experienced which stress.

Old suspects disappear

Scientists searching for a single cause have long been enticed by two late Eocene asteroid impacts, but the timing is off. Surface groups did not exhibit a corresponding impact-time collapse, but the minor bottom-dweller slide started prior to the large ice-sheet pulse.

Deep-ocean stress may have been exacerbated by later volcanism in the Afar-Arabian region, however there is still conflicting evidence to support this theory. Even when multiple environmental changes overlapped, no single catastrophe can adequately account for every biological turn in time.

Intelligence from fossil clocks

The sharper history was made feasible by a new evolutionary algorithm, a search technique that becomes better through variety and selection. The tool was created by Fan and colleagues at NJU to combine disparate local fossil ranges into a single chronology.

The computer produced a timeline with steps of about 29,000 years using roughly 40,000 occurrences from 1,269 species. One blended pattern and distinct loses, pauses, and rebounds were distinguished by that additional detail.

Reevaluating stories about extinction

For many years, the shift appeared to be a single marine extinction event followed by a straightforward recovery due to low-resolution summaries. The study's Chinese coverage stated clearly that it was "not a collective extinction, However, every group followed its own path.

Because various ecosystems might fail on very different clocks, this contrast helps scientists better understand other deep-time disasters. Additionally, it provides NJU and its partners with a model for re-examining past extinction narratives constructed from coarse bins.

Deep-time lessons

The Eocene-Oligocene transition appears as a layered ecological event rather than a single transformation occurring everywhere at once when viewed at high resolution. That doesn't mean that today's warming is a repeat, but it does demonstrate how rapid global change can separate winners and losers based on habitat.