NASA
New research has found the missing piece of the snowball Earth theory puzzle in the granite that forms Pikes Peak in Colorado.
About 700 million years ago, the Earth cooled so much that scientists believe huge sheets of ice enveloped the entire planet like a giant snowball. This global freeze, known as Snowball Earth, lasted tens of millions of years.
Yet, miraculously, primitive life not only maintained itself, it thrived. When the ice melted and the ground thawed, complex multicellular life emergedwhich eventually led to the forms of life we recognize today.
The Snowball Earth hypothesis has been largely based on evidence of sedimentary rocks exposed in areas that were once along coasts and shallow seas, as well as in climate models. Physical evidence that ice sheets covered the interior of continents in warm equatorial regions had eluded scientists – until now.
In a paper published in the journal Proceedings of the National Academy of Sciences, a team of geologists describes the missing linkfound in an unusual pebbly sandstone encapsulated in the granite that forms Colorado’s Pikes Peak.
Solving the mystery of Snowball Land on a mountain
Pikes Peak, originally called Tavá Kaa-vi by the Ute people, lends its ancestral name, Tava, to these remarkable rocks. They are composed of solidified sand injectionswhich formed similar to a medical injection, when a sand-rich fluid was forced into the underlying rock.
One possible explanation for the creation of these enigmatic sandstones is the immense pressure exerted by an ice sheet over Snowball Earth, which forced sediment mixed with meltwater into the weakened rock.
One obstacle to testing this idea, however, has been the lack of an age for the rocks that reveals when the appropriate geological circumstances existed for sand injection.
Research has found a way to solve this mystery, using iron veins found along Tava Bugs, near Pikes Peak and elsewhere in Colorado.
Iron minerals contain very low amounts of radioactive elements natural substances, including uranium, which slowly decays into the element lead at a known rate. Recent advances in laser-based radiometric dating have made it possible to measure the ratio of uranium and lead isotopes in the iron oxide mineral hematite to reveal how long ago individual crystals formed.
The iron veins appear to have formed before and after sand was injected into the Colorado bedrock: they found veins of hematite and quartz that cut across the Tava dikes and were crossed by Tava dikes. This allowed us to discover an age range for the sand injectites, which must have formed between 690 million and 660 million years ago.
So what happened?
The time period means that these sandstones formed during the Cryogenic Period, from between 720 million and 635 million years ago. The name derives from “cold birth” in ancient Greek and is synonymous with climate change and disruption of life on our planet – including Snowball Earth.
Although the factors that triggered the extreme cold at that time are debated, the prevailing theories involve changes in tectonic plate activityincluding the release of particles into the atmosphere that reflected sunlight away from Earth. Eventually, the accumulation of carbon dioxide resulting from the release of volcanic gases may have warmed the planet again.
The Tava found at Pikes Peak would have formed near the equator, in the heart of a ancient continent called Laurentiawhich gradually, over time and long tectonic cycles, moved to its current northern position in today’s North America.
The origin of the Tava rocks has been debated for over 125 yearsbut new technology has made it possible, for the first time, to relate them conclusively to the period of Cryogenic Snowball Earth.
The scenario imagined for sand injection is more or less the following:
A gigantic ice sheet with areas of geothermal heating at its base produced meltwater, which mixed with quartz-rich sediments. The weight of the ice sheet created immense pressures which forced this sandy fluid to penetrate the rock that had already been weakened for millions of years. Similar to what happens today with fracking to extract natural gas or oil, the pressure cracked the rocks and pushed sandy meltwater inward, eventually creating the injections we see today.
Clues to another geological puzzle
The new discoveries not only reinforce the global Snowball Earth hypothesis, but the presence of Tava injections in weak, fractured rocks once covered by ice sheets provides clues about other geological phenomena.
Temporal gaps in the rock record, created by erosion and called unconformities, can currently be observed throughout the United States, being the most famous is the Grand Canyonwhere, in some places, more than a billion years are missing. Unconformities occur when a prolonged period of erosion removes and prevents the formation of new layers of rock, leaving an unconformable contact.
The results support that a Great Unconformity near Pikes Peak must have been formed before Cryogenic Snowball Earth. This is at odds with hypotheses that attribute the formation of the Great Unconformity to large-scale erosion by Snowball Earth’s own ice sheets.
We hope the secrets of these elusive cryogenic rocks in Colorado will lead to the discovery of other Earth records from Snowball Earth. Such discoveries could help develop a clearer picture of our planet during climate extremes and the processes that led to the habitable planet we currently live on.
