Many of those with deep concerns about global warming are believers in a static earth, that is they would like to keep the planet the way it is. They fear that someone may soon be cultivating bananas in their Pennsylvania backyard.
Such thinking runs counter to the geological history because the earth is a dynamic work in progress.
Some 60 years ago even many geologists believed the continents were fixed. Then came the gradual acceptance of plate tectonics that showed the land masses floating on the inner layer of the earth building mountains and even causing earthquakes.
Once major concern even voiced by President Barack Obama is that global warming causes sea-level rise. That is true, and the seas have been rising since the peak of the Ice Age, perhaps 18,000 years ago. Some scientists place the increase at 120 meters.
But global warming appears to be a minor concern of humanity when compared to super volcanoes, 800-foot tsunami waves, plagues, droughts and giant earthquakes.
Now comes a report from the Royal Astronomical Society that says mass extinctions occurring over the past 260 million years were likely caused by comet and asteroid showers.
Said the society in a news release:
For more than 30 years, scientists have argued about a controversial hypothesis relating to periodic mass extinctions and impact craters caused by comet and asteroid showers on Earth.
In their paper, Michael Rampino, a New York University geologist, and Ken Caldeira, a scientist in the Carnegie Institution’s Department of Global Ecology, offer new
support linking the age of these craters with recurring mass extinctions of life, including the demise of the dinosaurs. Specifically, they show a cyclical pattern over the studied period, with both impacts and extinction events taking place every 26 million years.
This cycle has been linked to periodic motion of the Sun and planets through the dense mid-plane of the galaxy.
The Royal Astronomical Society said that the researchers prepared a timeline showing that five out of the six largest impact craters of the last 260 million years on earth correlate with mass extinction events.
“The correlation between the formation of these impacts and extinction events over the past 260 million years is striking and suggests a cause-and-effect relationship,” said Rampino in the news release.
One of the craters considered in the study is the large, 180-kilometer diameter Chicxulub impact structure in the Yucatan, which dates to about 65 million years ago, the time of a great mass extinction that included the dinosaurs.
The researchers did not address what may have been a much more recent massive comet strike in North America about 12,900 years ago. Scientists date the disaster because nanodiamonds have been found all over the continent in sediment of that time.
Paired with the fact that this layer occurs directly before the extinction of at least 35 genera of large mammals, including mammoths, it is strong circumstantial evidence for a cosmic event, said Scientific American in a 2009 article.
What ever happened stopped a warming trend and set off the more than 1,300-year cooling period in the Northern Hemisphere known as the Younger Dryas for the abundance of an alpine flower’s pollen found during the interval, the article said.