Geologists in Colorado have found compelling evidence that hundreds of millions of years ago, huge glaciers covered the Earth, stretching all the way to the equator, turning the planet into icicles drifting through space. The study, led by the University of Colorado Boulder, is a coup for proponents of a long-standing theory known as the "Snowball Earth."
The theory is that from about 720 million years ago to 635 million years ago, for reasons that are still unclear, a series of runaway events fundamentally changed the Earth's climate. Temperatures plummeted and ice, possibly miles thick, covered every inch of the Earth's surface.
"This study provides the first physical evidence that Snowball Earth reached the center of an equatorial continent," said Liam Courtney-Davies, first author of the new study and a postdoctoral researcher in the Department of Geological Sciences at the University of Colorado Boulder.
The research team published their findings on November 11 in the Proceedings of the National Academy of Sciences. Co-authors include Rebecca Flowers, professor of geological sciences at the University of Colorado Boulder, and researchers from Colorado College, the University of California, Santa Barbara, and the University of California, Berkeley.
The research focused on the frontier of Colorado's Rocky Mountains. Here, a series of sandstones nicknamed "Tavakaiv" or "Tava" provide clues to this cold period in Earth's past, Courtney-Davies said.
The researchers used a dating technique called laser ablation mass spectrometry, which shines a laser on the mineral, releasing some of its atoms. The results show that the rocks were forced into the ground about 690 million to 660 million years ago - most likely caused by huge glaciers pressing on top of the rocks.
Courtney-Davies added that the research will help scientists understand a key stage in Earth's geological history, but also in the history of life on Earth. The first multicellular organisms may have appeared in the oceans immediately after Snowball Earth thawed.
"Climate evolved, life evolved. All of these things happened during the Snowball Earth upheaval," he said. "We must better characterize this entire period to understand how we and the Earth co-evolved."
The term "Snowball Earth" can be traced back to a 1992 paper by American geologist Joseph Kirschvink.
However, despite decades of research, scientists still don't agree on whether the globe is actually frozen. For example, geologists have found traces of thick ice from this period in ancient coastal areas, but not in the interior of continents near the equator.
That's why Colorado comes into play. At that time, Colorado was not located at the northern latitudes it is today. In contrast, Colorado lies above the equator and was the inland portion of the ancient Laurentian supercontinent.
Scientists believe that if glaciers formed here, they could have formed anywhere.
In search of this missing piece of the puzzle, Courtney-Davis and his colleagues found the Tawa Sandstone. Today, these landforms poke out of the ground in several places in Colorado's Front Range, especially around Pikes Peak. To the untrained eye, they appear to be ordinary-looking tawny rocks arranged in vertical bands ranging from less than an inch to several feet wide.
But to geologists, these features have an unusual history. At some point in the past, they were likely sand on Colorado's surface. But then forces pushed them underground, digging like claws into the earth's crust.
"These are typical geological features called injectites that typically form beneath some ice sheets, including modern-day Antarctica," Courtney-Davies said.
He wondered whether the Tawa Sandstone was also related to the ice sheet. To do this, the researchers calculated the ages of mineral veins that cut through these landscapes. They collected tiny samples of minerals rich in iron oxide (essentially rust) and then shined lasers on them. In the process, these minerals release small amounts of the radioactive element uranium. Because uranium atoms decay into lead at a constant rate, the team could use them as timekeepers in Earth's rocks.
The team's findings indicate that the Tawa Sandstone was compressed underground during the "Snowball Earth" period. The team suspects that thick ice formed over Colorado at that time, exposing the sandstone to intense pressure. Eventually, with nowhere else to go, they were squeezed into the bedrock below.
"We are excited about the opportunity to unravel the mystery of the only Snowball Earth deposit ever discovered in Colorado," Flowers said.
The researchers' work isn't over yet: If such landforms formed in Colorado during Snowball Earth, Courtney-Davies said, they likely formed elsewhere in North America: "We want to get the word out and get others to try to find these landforms as well, helping us build a more complete picture of Snowball Earth."
Compiled from /ScitechDaily