Global warming gets all the press today but there was a time when pollution-caused global cooling was the concern - and if you map the planet's recent history, 90,000 out of every 100,000 years were ice ages and it's been 12,000 years since the last one so the historical reason for concern was not unfounded.  A new book, "The Late Eocene Earth - Hothouse, Icehouse, and Impacts" tackles what global cooling was like.

According to the book's editors, Christian Koeberl of the University of Vienna and Alessandro Montanari of the Observatorio Geologico di Coldigioco in Italy, the end of the Eocene and the Eocene-Oligocene (E-O) transition mark the most profound oceanographic and climatic changes of the past 50 million years of Earth's history.

Earth experienced global cooling beginning in the middle Eocene, with a sharp temperature drop of about two degrees Celsius in the Late Eocene. This drop was characterized by an increase in marine oxygen isotope values and significant floral and faunal turnovers. The global climate changes are commonly attributed to the expansion of the Antarctic ice cap following its gradual isolation from other continental masses. However, as examined in this volume, multiple extraterrestrial bolide impacts, possibly related to a comet shower that lasted more than two million years, may have played an important role in deteriorating the global climate.

The volume provides an excellent overview of conditions on Earth during the last few million years of the Eocene and around the time of the Eocene-Oligocene boundary. Chapters include an expanded look at Earth across time by Walter Alvarez and colleagues; an updated and enhanced understanding of the Eocene-Oligocene boundary transition using different climate proxies, improved time control, and climate models; integrated stratigraphy of the late Eocene-early Oligocene transition and reevaluation of the Global Stratotype Section and Point (GSSP); paleoecology and paleoclimate through the critical period of transition from hothouse to icehouse; and Late Eocene impact processes and impact stratigraphy.