English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

In this issue of PNAS, Kent and Muttoni (1) offer an explanation of why Earth, after being hot 50 million years ago, cooled dramatically, changing its climatic state. What were these states, and how did they come to be recognized? In the early 20th century, Vladimir Köppen (2) classified present climate into five main types based on the idea that native vegetation is its best expression. There is an overall latitudinal zonation reflecting the gradient in mean temperature from pole to equator, with lateral variations arising from variability in rainfall and continentality. To determine the past distribution of climate zones, he, in collaboration with his son-in-law Alfred Wegener (2), compiled occurrences of climate sensitive deposits and fossils and plotted them on Wegener's newly minted continental drift maps back to the Devonian (350 Ma). Assuming that Köppen's present-climate model always applied, they constructed poles and parallels of geographic latitude (2). But their maps contained certain inconsistencies and failed to explain certain phenomena, not because there were gross errors in the data, but because climate zones were not always the same as at present. Inconsistencies became increasingly evident as Early Cenozoic and especially Eocene floras of “tropical” aspect were found in northern Europe and Greenland, and floras of temperate aspect were found in the Canadian arctic islands, much farther north that would be expected. As …

Why Earth became so hot 50 million years ago and why it then cooled