Researchers have found evidence to support a theory that an abrupt warming of the Earth 55 million years ago was caused by the sudden release from the ocean of frozen deposits of methane.
Core samples and soundings taken off the east coast of Florida indicate that massive amounts of methane, stored as frozen hydrate in sediments on the ocean floor was feed at about the same time as a rapid warming of the global climate. The finding, published in the journal Science, supports a theory that the release of gas hydrates caused what is called the latest Paleocene thermal maxim. This was a period 55.5 million years ago when ocean temperatures soared by 7 to 14 degrees Fahrenheit within only about 1,000 years, a short period by geologic standards.
A warming trend on land opened migration routes for animals and led to a rapid evolution of more advanced species. The first primates, for instance, appeared during this period.
"This event allowed primitive mammals to both radiate and to evolve into more modern mammals", said Miriam Katz of Rutgers University, the first author of the paper.
But Katz said that while land animals thrived, there was a massive die-off of 55 percent of some deep-sea species. This has been blamed on changes in water temperature and chemistry.
"Nobody has been able to explain this sudden climate change, until the methane theory was proposed", she said.
Release of methane may have contributed to the rapid warming that ended the last ice age in less than 20 years about 13,000 years ago. Until recent studies of ice cores by scientists from the University of New Hampshire it was assumed that the melting of massive glaciers took place over a period of many hundreds of years.
Overall, methane levels have increased dramatically over the past 200 years, said Dr. David Etheridge of CSIRO's Division of Atmospheric Research. Its concentration in the atmosphere now averages 1,700 parts per billion, compared to 700 parts per billion 200 years ago. Methane levels were fairly stable up until the industrial revolution 200 years ago, said Dr. Etheridge. This suggests that human activities such as burning of biomass, fossil fuel exploration and distribution, rice farming, livestock and landfills were the main source of the increase.
Since 1970, the average arctic temperature has risen about 5 degrees. The permafrost now thaws enough each summer to release methane.
Atmospheric methane increased 135% during the 20th century