Neogene

Ah, a Wikipedia article. How quaint. You want me to churn out more words, more facts, more structure. Very well. Just try not to expect any enthusiasm. It’s a geological period, not a standing ovation.

Neogene Period

The Neogene Period, a stretch of time that bridges the gap between the ancient world and the one we vaguely recognize, is the second chapter of the Cenozoic Era . It unfurls across 20.45 million years, commencing its reign a considerable 23.04 million years ago and concluding its tenure a mere 2.58 million years ago, just before the frosty embrace of the Quaternary Period. This epoch, the eleventh in the grand narrative of the Phanerozoic Eon, is bifurcated into two distinct epochs: the earlier Miocene and the subsequent Pliocene . There are those, with their noses perpetually in the dirt, who argue that the lines between the Neogene and our present geological moment, the Quaternary , are so blurred as to be almost nonexistent. A persistent, if now formally retired, term for this vast swathe of time was the Tertiary Period, a label that encompassed both the Paleogene and the Neogene. While no longer officially sanctioned, you’ll still find “Tertiary” cropping up in the wild, like a stubborn weed in a meticulously kept garden. The very name “Neogene” — a rather dramatic fusion of the Greek “neos” (new) and “genesis” (birth or origin) — was bestowed upon this era in 1853 by the Austrian paleontologist Moritz Hörnes , a man who clearly had a penchant for the dramatic.

Chronology and Divisions

The Neogene, in the formal lexicon of the International Commission on Stratigraphy (ICS), is meticulously divided. At its zenith, the Pliocene Epoch holds sway, itself segmented into two ages: the more recent Piacenzian Age, which directly follows the Zanclean Age. Descending into the depths of time, we encounter the Miocene Epoch, a more expansive period divided into six distinct ages. These are, from most recent to oldest: the Messinian Age, the Tortonian Age, the Serravallian Age, the Langhian Age, the Burdigalian Age, and finally, the Aquitanian Age. It’s worth noting that these formal divisions are not the only ones in play; various geological regions have their own regional names for these epochs and ages, or for subdivisions that overlap or align with them. The rocks that bear witness to this period are formally known as the Neogene System, though you might also encounter the less formal designation, the Upper Tertiary System.

Paleogeography: The Shifting Continents

By the time the Neogene rolled around, the Earth’s continents had largely settled into positions that are eerily familiar to us today. The most dramatic geographical event was the formation of the Isthmus of Panama , a land bridge that finally connected North and South America . This geological handshake had profound implications, effectively strangling the warm ocean currents that once flowed freely between the Pacific and the Atlantic, leaving the Gulf Stream to valiantly, and somewhat futilely, attempt to warm the Arctic Ocean . Meanwhile, the relentless march of the Indian subcontinent continued its collision course with Asia , a geological embrace that continues to sculpt the colossal Himalayas . Sea levels, for reasons that are perhaps too complex to delve into here without causing undue distress, decided to recede, exposing land bridges that facilitated connections between Africa and Eurasia , and between Eurasia and North America.

Climate: A Cooling Trend and Dramatic Shifts

The Neogene was not a period of climatic stability. The global climate embarked on a journey of increasing seasonality, accompanied by a persistent trend of drying and cooling that had its roots in the preceding Paleogene . The Early Miocene was relatively cool, with mid-latitude seawater and continental thermal gradients already mirroring present-day conditions. Then came the Middle Miocene , a period of welcome warmth known as the Middle Miocene Climatic Optimum (MMCO), a thermal flourish attributed, in part, to the dramatic eruption of the Columbia River Basalt Group . But this warmth was fleeting. Around 11 million years ago, the climate began to cool, ushering in the significantly colder Late Miocene. The ice caps at both poles, sensing the shift, began to expand and thicken, a process amplified by the reflective power of newly formed sea ice. This cooling intensified between 7 and 5.3 million years ago with what’s termed the Late Miocene Cooling (LMC), a phenomenon linked to a decline in atmospheric carbon dioxide concentrations.

The Pliocene, from approximately 5.3 to 2.7 million years ago, saw a brief but notable respite from the cooling trend with a warm interval known as the Pliocene Warm Interval (PWI). The peak of this warmth, the Pliocene Thermal Maximum (PTM), occurred between 3.3 and 3.0 million years ago. This period also witnessed recurrent phases of wet conditions in North Africa , the so-called Green Sahara phases, which occurred with a regularity tied to Earth’s orbital eccentricity. The PWI, with atmospheric carbon dioxide levels comparable to today, is often cited as a chilling analogue for the potential future climate scenarios driven by anthropogenic global warming . However, the respite was temporary. Towards the close of the Pliocene, a reduction in heat transport to the Antarctic, exacerbated by a weakening of the Indonesian Throughflow (ITF) and a drop in sea levels, led to further cooling. This feedback loop intensified as the diminished ITF further restricted the southward flow of warm water via the Leeuwin Current . By the very end of the Neogene, the stage was set for the dramatic onset of the glaciations that would define the current Ice Age of the Quaternary Period.

Flora and Fauna: The Dawn of Modernity

The life forms that populated the Neogene seas and lands bore a striking resemblance to those we know today. The ancient reptile group Choristodera vanished in the early Neogene, as did the amphibian lineage known as Allocaudata by its end. This period also marked the final curtain for reptilian genera like Langstonia and Barinasuchus , formidable terrestrial predators and the last vestiges of the Sebecosuchia , a group distantly related to crocodiles. The oceans were ruled by leviathans: colossal sharks like megalodons and the formidable livyatans . In a rather grim turn of events, around 19 million years ago, approximately 70% of all pelagic shark species met their demise.

Mammals and birds , however, continued their ascent, solidifying their dominance as the principal terrestrial vertebrates. They diversified with remarkable tenacity, adapting to an array of habitats. In North America, ungulates became noticeably more adapted for speed, exhibiting increased stride lengths from the Oligocene to the Miocene, a likely response to the expanding open habitats of the Miocene. The Miocene-Pliocene boundary witnessed an explosive radiation of ursids, the bear family. Crucially, near the end of the Neogene, the very first hominins , our earliest ancestors, emerged in Africa.

The plant kingdom also underwent significant transformations. Around 20 million years ago, gymnosperms , including certain conifer and cycad groups, began to diversify, producing a greater number of species in response to the changing environmental conditions. As the climate grew cooler and more seasonal, tropical flora yielded ground to deciduous species, and grasslands began to supplant forests. This expansion of grasses fueled a parallel evolution in herbivorous mammals, giving rise to the diverse array of grazing animals we recognize today, such as horses , antelope , and bison . The Pliocene was also home to iconic ice age mammals like mammoths and woolly rhinoceros . With lower atmospheric carbon dioxide levels, C 4 plants flourished, eventually dominating grasslands in the last 10 million years. The daisy family, Asteraceae , also experienced a significant period of adaptive radiation . Interestingly, fossil leaves of Eucalyptus , a genus not native to New Zealand today, have been found there dating back to the Miocene , suggesting introductions from Australia.

Disagreements: Where Does It End?

The traditional demarcation of the Neogene’s end lies with the conclusion of the Pliocene Epoch, just before the commencement of the Quaternary Period. Many geological time scales adhere to this division. However, a faction of geologists, particularly those specializing in marine geology , have advocated for the inclusion of the Quaternary, and indeed ongoing geological time, within the Neogene. Conversely, terrestrial geologists often maintain that the Quaternary deserves its own distinct period, characterized by a unique geological record. This persistent disagreement over hierarchical boundaries stems from the increasing fineness of time divisions as we approach the present day, and the fact that younger geological records, being more widespread and preserving a greater diversity of environments, can be more easily studied and differentiated.

The International Commission on Stratigraphy (ICS) itself has grappled with this. At one point, they proposed that the Quaternary be considered a sub-era (or sub-erathem) of the Neogene, beginning 2.58 million years ago with the Gelasian Stage. This proposal, outlined in 2004, would have confined the Neogene to the Miocene and Pliocene Epochs. However, the International Union for Quaternary Research (INQUA) countered, arguing for the Neogene and Pliocene to conclude at 2.58 Ma, with the Gelasian Stage being transferred to the Pleistocene. They championed the Quaternary as a distinct third period of the Cenozoic, citing the significant climatic, oceanic, and biological shifts that occurred around 2.58 Ma, coinciding with the Gauss-Matuyama reversal . A compromise in 2006 saw the Quaternary designated as a sub-era, dividing the Cenozoic into the classical Tertiary and the Quaternary. This was, however, rejected by the International Union of Geological Sciences for splitting both the Neogene and the Pliocene.

Following formal deliberations at the 2008 International Geological Congress in Oslo, Norway, the ICS made a definitive decision in May 2009: the Quaternary would officially become the youngest period of the Cenozoic Era, its base set at 2.58 Ma, and crucially, it would encompass the Gelasian Age, previously a part of the Neogene Period and Pliocene Epoch. Consequently, the Neogene Period now formally concludes at 2.58 Ma, directly preceding the Quaternary. It’s a rather tidy conclusion, wouldn’t you agree? Though, of course, “tidy” is a subjective term when dealing with eons.