Ancient ocean water discovery is unlocking secrets of Earth's past

High in the Himalayas, a new discovery has emerged that will ultimately shed light on the mysteries of Earth’s past. An international team of scientists from the Indian Institute of Science (IISc) and Niigata University in Japan has found drops of water preserved in mineral formations that are believed to have originated from an ancient ocean dating back around 600 million years.

“We have found a time capsule for paleo oceans,” said study lead author Prakash Chandra Arya. A detailed examination of these deposits, which contain both calcium and magnesium carbonates, has enabled the researchers to propose a potential sequence of events leading up to a pivotal period of oxygenation in Earth’s history.

Unlocking Earth’s past 

According to the widely held scientific consensus, between 700 and 500 million years ago, the Earth experienced a prolonged period of intense glaciation known as the “Snowball Earth” glaciation. Following this icy era, there was a dramatic rise in the Earth’s atmospheric oxygen levels, known as the Second Great Oxygenation Event. 

This oxygen increase, it’s believed, played a crucial role in the emergence of complex life forms. The connection between these two monumental events, however, has remained obscure, due to a lack of well-preserved fossils and the disappearance of oceans from that epoch. But the discovery of marine rocks in the Himalayas could potentially provide a key to these mysteries.

“We don’t know much about past oceans,” said Arya. Questions about the composition, temperature, and acidity of the primeval seas continue to perplex researchers. Gaining insights into these aspects could help us comprehend Earth’s past climate patterns, a resource that would be invaluable for improving current climate models.

What the researchers learned 

The team’s analysis of the Himalayan mineral deposits, which date back to the Snowball Earth glaciation, reveals that these basins experienced a lengthy period of calcium deprivation. This depletion is thought to be due to a drop in riverine input. 

“During this time, there was no flow in the oceans, and hence no calcium input. When there is no flow or calcium input, as more calcium precipitates, the amount of magnesium goes up,” said study co-author Professor Sajeev Krishnan. He suggests that the magnesium-rich deposits from this era managed to capture and preserve remnants of ancient ocean water as they crystallized.

This scarcity of calcium would have also resulted in a nutrient deficiency, providing the perfect conditions for the flourishing of slow-growing photosynthetic cyanobacteria. These microorganisms, in turn, likely started releasing an increased amount of oxygen into the atmosphere. Arya explained: “Whenever there is an increase in the oxygen level in the atmosphere, you will have biological radiation (evolution).”

Ancient ocean deposits 

The ancient ocean deposits were found scattered along a substantial stretch of the western Kumaon Himalayas, from Amritpur to the Milam glacier and Dehradun to the Gangotri glacier region. 

With meticulous laboratory testing, the researchers verified that these deposits were indeed the product of ancient ocean water precipitation and not originating from other sources, like submarine volcanic activity within the Earth’s interior.

The scientists are hopeful that these ancient deposits can unlock details about the prehistoric ocean conditions, such as pH levels, chemistry, and isotopic composition. This knowledge could help answer questions related to the evolution of oceans and, by extension, life on Earth. The study is published in the journal Precambrian Research.

More about ancient oceans

Ancient oceans, also known as paleo-oceans, hold significant importance in understanding the Earth’s past and the evolution of life. These bodies of water existed hundreds of millions to billions of years ago and played a pivotal role in shaping the Earth’s climate, geological features, and biological diversity.

While modern oceans cover about 70% of the Earth’s surface, it is believed that ancient oceans might have been even more extensive due to the Earth’s hotter, more volatile climate. There were fewer landmasses to obstruct the flow of water, leading to vast, interconnected oceanic bodies.

Composition

The chemical composition of these ancient oceans was very different from what we observe today. For instance, the Archean oceans (4 to 2.5 billion years ago) were probably rich in iron. There was less oxygen available because photosynthetic organisms, which produce oxygen, hadn’t yet evolved. 

When photosynthetic organisms did begin to proliferate around 2.4 billion years ago in what’s known as the Great Oxidation Event, they started to release oxygen which reacted with the iron, leading to the formation of iron oxide that settled to the ocean floor. This event drastically changed the composition of the oceans and the atmosphere, setting the stage for the evolution of more complex life forms.

Research 

Investigating the properties of ancient oceans is a challenging task. Direct evidence, such as water trapped in rocks (like the example in the Himalayas), can provide valuable information. Scientists also study the composition of ancient marine sediments, isotopic ratios, and other geological signatures to infer characteristics of the Earth’s early seas.

These insights into ancient oceans are not only important for understanding Earth’s past but also for predicting its future, particularly in relation to climate change. Understanding how Earth’s climate and life evolved in response to changes in the oceans can help us model and predict how ongoing changes in ocean temperature, acidity, and circulation might influence future climate and ecosystems.

More about Snowball Earth

Snowball Earth refers to a geological hypothesis proposing that the Earth was entirely, or nearly entirely, covered in ice for extended periods in the Earth’s distant past.

The concept primarily concentrates on the Neoproterozoic era, specifically between 750 to 580 million years ago. The American geologist Joseph Kirschvink coined the term ‘snowball Earth’ in 1992 to represent a severe global climate condition.

Geological Evidence

The evidence supporting the snowball Earth hypothesis is diverse, ranging from glacial sedimentary deposits to isotopic signatures. Glacial tillites and dropstones, found in tropical latitudes, are key evidence suggesting a near-global or global glaciation. Icebergs appear to have deposited these sediments into open water. This suggests that ice covered most, if not all, of the world’s oceans.

On a chemical level, the cap carbonates lying above glacial deposits exhibit unusual isotopic ratios of carbon and sulfur. This suggests a rapid change in the carbon cycle at the end of the glaciation period. One possibility is an extraordinary proliferation of photosynthetic life once the ice retreated.

The Sturtian and Marinoan Glaciations

The Snowball Earth hypothesis mainly focuses on two glaciations – the Sturtian and Marinoan.

The Sturtian glaciation occurred approximately 720 to 680 million years ago.

The Marinoan glaciation, which followed, lasted from 650 to 635 million years ago.

Both glaciations left a similar geological footprint, providing compelling evidence for the occurrence of global ice cover.

Triggering Mechanisms

The exact mechanisms that initiated these severe glaciations remain under debate. Some scientists propose that a decrease in solar radiation output or changes in the Earth’s orbit could have triggered such a glaciation. Alternatively, the gradual removal of greenhouse gases from the atmosphere due to weathering processes might have played a role.

One prevailing theory is that the breakup of the supercontinent Rodinia led to increased weathering of silicate rocks. This drew down carbon dioxide from the atmosphere and initiated a global cooling.

The Earth’s Recovery

The recovery from the snowball Earth condition is another intriguing aspect of the hypothesis. One explanation posits that volcanic outgassing of carbon dioxide could have built up a greenhouse effect over time. This would have eventually lead to ice melt.

When the ice began to retreat, a positive feedback effect would take over. Ice reflects sunlight, but the newly exposed rock and water would absorb sunlight. This accelerated the warming and lead to a swift end to the glaciation.

Life During Snowball Earth

Despite the harsh climatic conditions, life appears to have survived during the snowball Earth periods. Some microorganisms, like cyanobacteria, could have continued photosynthesis in open water refugia near the equator or beneath the ice.

The dramatic changes in climate and environment during these periods might have spurred the evolution of multicellular life. In addition, these changes may have also spurred the radiation of complex life in the Ediacaran and Cambrian periods that followed the last Snowball Earth event.

Criticism and Alternatives to Snowball Earth Hypothesis

While many widely accept the snowball Earth hypothesis, it does encounter criticism and competes with alternative theories. Critics argue that some areas of the Earth may have remained ice-free, suggesting a ‘slushball Earth’ scenario. They base their arguments on the existence of certain sedimentary structures that typically form in non-glacial environments and on the survival and evolution of life during these periods.

Snowball Earth represents a significant hypothesis in understanding our planet’s climatic past and the resilience and evolution of life. The extreme conditions of this period showcase Earth’s potential for radical change and provide crucial insights into the Earth’s climate system.

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