Huge chunks of ancient rock uncovered by scientists in Australia may help explain sunspot cycles and changes in Earth's atmosphere during the ages preceding the reign of the dinosaurs.
Sunspots are the dark, irregularly shaped blotches on the sun's surface that appear in recurrent cycles and are caused by solar magnetic storms.
Scientists say the spots are both darker and cooler than the rest of the sun's surface and new evidence suggests sunspot cycles may have occurred with the same regularity since prehistoric times.
The evidence was found in 700-million-year-old layers of banded sandstone that once lay at the bottom of an Ice Age lake in Australia. The rocks were deeply marked with lines that were first embedded during the Precambrian geological period.
20,000 Years of Activity
"There are about 20,000 years of this recorded in the rock and that is a marvelous thing because we've only had a couple hundred years of recorded sunspot activity, now we have 100 times as much to work with," said Ronald Bracewell, a Stanford University astronomer in Palo Alto.
"About every half an inch or so you can see a dark line running across it for about 100 feet and that fact is evident as soon as you look at it," he said.
So far, markings on the rocks have enabled Bracewell to extrapolate from present sunspot activity back to the year 1800. He plans to record cycles even further back in time as his research of sunspot activity continues.
But interestingly enough, Bracewell hypothesizes, the markings were not burned into the sandstone by the sun but by a combination of events that initially were enhanced by Earth's lack of a protective shield of gases.
"During the Precambrian period, Australia was a permafrost region just like Alaska and in the spring the ice would melt," Bracewell explained.
The striations in the rock were caused by layers of silt laid down annually at the bottom of what was then a lake bed.
"The quantity of silt would depend on the quantity of water that ran off," he said. "If it was a warm spring, a lot of ice would melt, and a more than average amount of silt would be deposited."
12 Layers Across
Bracewell said his work relies heavily on that of Australian geoastronomer George Williams, the original discoverer of the rocks. Williams was the first to notice that the striations occurred in groups that averaged about 12 layers across, but ranged from eight to 14.
Sunspot cycles also range between eight and 14 years and it is that relationship that prompted Bracewell to agree that the lines were caused by activity occurring on the sun's surface.
"It's so regular that it's obviously totally under solar control," he said.
Bracewell said scientists speculate that during prehistoric times sunspots controlled weather conditions on Earth by determining spring runoff in glaciated areas.
He thinks that this occurred when ultraviolet rays beamed directly to Earth without being deflected by the ozone layer which now blocks out most of the ultraviolet rays emitted by the sun.
As for sunspots, Bracewell said many people today believe they "have an effect on drought in the Great Plains," and if that is so, a better understanding of the cycles ultimately could have importance for agriculture.