'Missing Link' Found in Ancient Colorado Rocks Shows Snowball Earth Really Happened

About 700 million years ago, Earth it got so cold that scientists believe massive ice sheets covered the entire planet like a giant snowball. This global freeze, known as Snowball Earthendured for tens of millions of years.

Yet, miraculously, early life it not only endured but thrived. When the ice melted and the earth thawed, complex multicellular life emergedeventually leading to life forms we recognize today.

The Snowball Earth Hypothesis was largely based on evidence from sedimentary rocks exposed in areas which they were once along the coasts and shallow seas as well climate modeling. Physical evidence that ice sheets covered the interior of continents in warm equatorial regions has eluded scientists—until now.

In new research published in the Proceedings of the National Academy of Sciences, our team of geologists describes the missing link found in an unusual gravelly sandstone encased in the granite that forms Pikes Peak in Colorado.

An illustration of the Earth covered in ice

The Earth froze during the Cryogenian period, but life on the planet survived. (Image credit: NASA)

Solving a Snowball Earth Mystery on a Mountain

Pikes Peak, originally called Tavá Kaa-vi by the Ute people, lend their ancestral name, Tava, to these notable rocks. I am composed of solidified injected sandwhich formed in a manner similar to a medical injection when the sand-rich fluid was forced into the underlying rock.

One possible explanation for what created these enigmatic sandstones is the immense pressure of a snowball Earth ice sheet forcing sediment mixed with meltwater into the loose rock below.

A person holding a multicolored stone

Dark red to purple sandstone bands Tava dissects pink and white granite. The tray is also cross-cut with silver-grey veins of iron oxide. (Image credit: Liam Courtney-Davies)

One obstacle to testing this idea, however, was the lack of an age for the rocks that would reveal when the right geologic circumstances existed for sand injection.

A photograph of a granite wall with a vertical shaft of rock of different texture

A nearly vertical 5-foot-tall Tava dike is evident in this section of Pikes Peak granite. (Image credit: Liam Courtney-Davies)

I found a way to solve that mystery, using veins of iron found alongside Tava injectites near Pikes Peak and elsewhere in Colorado.

Iron minerals contain very small amounts of naturally occurring radioactive elements, including uranium, which slowly decay decays to lead at a known rate. Recent advances in laser-based radiometric dating allowed us to measure the ratio of uranium to lead isotopes in the iron oxide mineral hematite to reveal how long ago the individual crystals formed.

The iron veins appear to have formed both before and after the sand was injected into the bedrock of the Colorado: We found hematite and quartz veins that cut both the Tava dykes and were cross-cut by the Tava dykes. This allowed us to find 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 were formed during the Cryogenian period, from 720 million to 635 million years ago. The name derives from “cold birth” in ancient Greek and is synonymous with climate change and the disruption of life on our planet – including snowball Earth.

While the triggers for the extreme cold at the time are debated, prevailing theories involve changes in the activity of tectonic platesincluding the release of particles into the atmosphere that reflect sunlight away from Earth. Finally, a accumulation of carbon dioxide from volcanic release may have warmed the planet again.

How did the earth become a giant snowball? – YouTube

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The tray found on Pikes Peak would have formed near the equator in the heart of a the ancient continent called Laurentiawhich gradually over time and long tectonic cycles moved to its current northern position in North America today.

The origin of the Tava rocks has been debated for over 125 yearsbut new technology has allowed us to conclusively link them to the Cryogenian Snowball Earth period for the first time.

The scenario we envision for how the sand injection took place looks something like this:

A huge ice sheet with areas of geothermal heating at its base produced meltwater, which mixed with the quartz-rich sediment below. The weight of the ice sheet created immense pressures that forced this sandy fluid into bedrock that had already been weakened over millions of years. Similar to fracking for natural gas or oil today, the pressure cracked the rocks and pushed out the sandy meltwater, ultimately creating the injectites we see today.

Clues to another geological puzzle

Not only do the new findings further cement the global snowball Earth hypothesis, but the presence of Tava injectites in weak, fractured rocks once overlain by ice sheets provides clues to other geological phenomena.

Time gaps in the rock record created by erosion and called nonconformities it can be seen today in the United States, most famously at the Grand Canyon, where in places over a billion years of time are missing. Unconformities occur when a sustained period of erosion removes and prevents the formation of newer layers of rock, leaving an unconformable contact.

An aerial photo of the Grand Canyon

The Grand Canyon Unconformity is evident here, where horizontal layers of 500-million-year-old rock lie above a mass of 1,800-million-year-old rock. The discrepancy or “time gap” demonstrates that years of history are missing. (Image credit: Mike Norton via Wikimedia, CC BY-SA)

Our results argue that a large unconformity near Pikes Peak must have formed before the Cryogenian Snowball Earth. This contradicts the hypotheses that attribute the formation of the Great Unconformity large scale erosion of the Snowball Earth ice sheets themselves.

Hopefully, the secrets of these elusive cryogenic rocks in Colorado will lead to the discovery of other terrestrial records of snowball Earth. Such discoveries can help develop a clearer picture of our planet during climate extremes and the processes that led to the habitable planet we live on today.

This edited article is republished from conversation under a Creative Commons license. Read on original article.

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‘Missing Link’ Found in Ancient Colorado Rocks Shows Snowball Earth Really Happened

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