[6] The hyperthermals were geologically brief time intervals (<200,000 years) of global warming and massive input of isotopically light carbon into the ocean and atmosphere.
[7][8] The most extreme and best-studied event, the Paleocene-Eocene Thermal Maximum (PETM or ETM-1), occurred about 1.8 million years before ETM-2, at approximately 55.8 Ma.
The number, nomenclature, absolute ages and relative global impact of the Eocene hyperthermals are the source of much current research.
[9][10] In any case, the hyperthermals appear to have ushered in the Early Eocene Climatic Optimum (EECO), the warmest sustained interval of the Cenozoic Era.
[5] However, in sections deposited along continental margins (for example those now exposed along the Waiau Toa / Clarence River, New Zealand), the clay-rich horizon represents dilution by excess accumulation of terrestrial material entering the ocean.
[13] Somehow carbon input was coupled to an increase in Earth surface temperature and a greater seasonality in precipitation, which explains excess terrestrial sediment discharge marking both events in continental margin sections.
[15] Along the Atlantic Coastal Plain, changes in local hydrology and nutrient supply were minimal, unlike during the PETM.