Early Palaeozoic Icehouse
Encyclopedia
The Early Palaeozoic Icehouse was a cool period that interrupted the greenhouse temperatures of the Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...

 and Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...

 periods, culminating in the Hirnantian glaciation and the Ordovician extinction event. The icehouse was formerly thought only to consist of the Hirnantian glaciation itself, but has now been recognized as a longer, more gradual event.
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