What did Earth look like in the Neogene? (23.04–2.58 Ma)

Key events of this period

• Early Hominins

  6 Ma

  African fossils around 7–6 million years old, including Sahelanthropus, lie near the early history of the human lineage. Evidence for upright walking coexists with traits suited to climbing, and interpretations of the earliest fossils remain debated. Human evolution was a branching process, not a single moment when a modern-style walker appeared.

  References: Sahelanthropus tchadensis (Smithsonian Human Origins) · Walking Upright (Smithsonian Human Origins) · Earliest evidence of hominin bipedalism in Sahelanthropus tchadensis (2026)

• Caspian Sea isolation

  5.5 Ma

  Around 5.5 million years ago, the Caspian basin, once part of the Paratethys, became separated from the Black Sea basin. Falling water levels are studied as a factor in severing connections between the basins. This was one stage in the Caspian’s formation: later rises reconnected it with the Black Sea.

  References: Vasiliev et al. (2011): Magnetostratigraphy and radio-isotope dating of upper Miocene–lower Pliocene sedimentary successions of the Black Sea Basin · de la Vara et al. (2016): Quantitative analysis of Paratethys sea level change during the Messinian Salinity Crisis · Van Baak et al. (2019): Flooding of the Caspian Sea at the intensification of Northern Hemisphere Glaciations

• Messinian crisis & Mediterranean refilling

  5.33 Ma

  Restricted Atlantic exchange left enormous salt deposits in the Mediterranean between 5.97 and 5.33 million years ago. Marine conditions returned around 5.33 million years ago; Sicilian erosion features support a rapid refilling flood. How far water levels fell, and exactly how refilling unfolded, remain debated.

  References: Micallef et al.: Land-to-sea indicators of the Zanclean megaflood

• Panama Isthmus

  3 Ma

  Islands and shallow seas changed gradually; the final land bridge formed about 2.8 million years ago, connecting continents and restricting exchange between oceans. Relatives of horses and camels spread south; ground sloths and glyptodonts spread north. Some animals crossed before the land bridge was complete. At a separate historical date, the Panama Canal opened in 1914. Locks raise and lower ships to cross a lake; this did not restore the ancient seaway.

  References: O’Dea et al. (2016), Formation of the Isthmus of Panama · Formation of the Isthmus of Panama — full paper (2016) · Panama Canal Authority — History of the Panama Canal

• Northern Hemisphere Ice Sheets Expand

  2.6 Ma

  Northern Hemisphere glaciation intensified around 2.7–2.6 million years ago, within a longer cooling trend. Changes in Earth’s orbit and tilt paced repeated cold and warm intervals, with feedbacks from ice, oceans and greenhouse gases. The cycles later grew longer, shifting from roughly 41,000 to 100,000 years.

  References: Role of land-ocean interactions in stepwise Northern Hemisphere Glaciation (2024) · Milankovitch (Orbital) Cycles and Their Role in Earth’s Climate (NASA, 2020)