Greenhouse Worlds

The Cretaceous Period

During the Cretaceous period some 100 million years ago, Earth was a greenhouse. There were no ice caps and sea level was up to 200 m higher than it is now, flooding large portions of continents and creating inland lakes and seas. By 200 million years ago, the great super-continent of Pangea had begun to break apart, evolving toward the present-day configuration of our continents. Throughout the Cretaceous period, there is evidence that palm trees and reptiles were present in the interior of the continents north of the Arctic Circle. It is likely that CO2 levels were significantly elevated relative to today, but it remains a mystery how polar continental interiors could have remained so warm throughout the year.

Rapid Warming at the Paleocene-Eocene Thermal Maximum

During the Paleocene-Eocene Thermal Maximum (PETM) 55 million years ago, several thousand gigatons of carbon were added to the ocean atmosphere system in a period of centuries to a few millennia, resulting in a substantial increase in global temperatures and acidification of the ocean. As such, this event provides an important natural example of ocean’s response to warming and rapid carbon input. Significantly, the source of the carbon and the trigger for its release are not known, raising questions about the potential for large carbon releases from natural reservoirs such as permafrost and seafloor methane hydrates in response to future warming.

Anoxic Oceans in the Permian?

At the Permo-Triassic extinction – the largest mass extinction, 250 million years ago – and several other periods in Earth’s history, substantial portions of the ocean appear to have had extremely low oxygen levels. We have little knowledge of what triggered these events and how low oxygen levels could have been maintained in a circulating ocean. As most periods of ocean anoxia in Earth history occurred in warm climates, it is important to establish their relationship to climate.

Key Questions We’re Exploring
  • What sets the pole-equator temperature gradient in warm climates?
  • What were the drivers of past periods of ocean anoxia?
  • What was the source of carbon released at the PETM? What triggered its release and what were its consequences?
  • How did the ocean and its biological communities respond to past periods of ocean acidification?