In the Himalayas, researchers from the Indian Institute of Science (IISc) and Niigata University, Japan, have discovered water droplets bound in mineral deposits that were likely left behind by an ancient ocean that existed approximately 600 million years ago. The analysis of the deposits, which contained both calcium and magnesium carbonates, also allowed the team to provide a possible explanation for events that may have contributed to a major oxygenation event in Earth's history, according to a press release issued by the IISc in Bengaluru on Thursday.
"We have found a time capsule for paleo oceans," says Prakash Chandra Arya, PhD student at the Centre for Earth Sciences (CEaS), IISc, and lead author of the research published in 'Precambrian Research'.
According to the statement, scientists believe that between 700 and 500 million years ago, the Snowball Earth glaciation (one of the main glacial events in Earth's history) covered the planet for an extended period.
The subsequent increase in the amount of oxygen in the Earth's atmosphere, known as the Second Great Oxygenation Event, eventually lead to the evolution of complex life forms, so the theory goes.
IISc noted that, due to the lack of well-preserved fossils and the disappearance of all previous oceans in Earth's history, scientists have not completely understood how these events are related. However, exposures of marine rocks in the Himalayas can provide some answers.
Arya states, "We do not know much about past oceans." How dissimilar or similar were they to the oceans of today? What was their acidity, alkalinity, nutrient content, temperature, and isotopic composition?" Such insights could also provide clues about the Earth's climate in the past, and this information is helpful for climate modelling, he adds.
The deposits discovered by the team, which date back to roughly the time of the Snowball Earth glaciation, revealed that the sedimentary basins were devoid of calcium for an extended period of time, most likely due to low riverine input.
"During this period, there was no ocean current, and consequently no calcium input. When there is no flow or calcium input, the quantity of magnesium increases as more calcium precipitates, explains CEaS Professor Sajeev Krishnan, the study's corresponding author. The researchers hypothesise that the magnesium deposits formed at this time were able to capture paleo-ocean water in their pore space as they crystallised.
Calcium deficiency also likely resulted in a nutrient deficiency, creating a favourable environment for slow-growing photosynthetic cyanobacteria, which may have begun emitting more oxygen into the atmosphere.
"Whenever there is an increase in the oxygen level in the atmosphere, you will have biological radiation (evolution)," says Arya.
The team searched for these deposits from Amritpur to the Milam glacier and Dehradun to the Gangotri glacier region in the western Kumaon Himalayas.
Using extensive laboratory analysis, they were able to confirm that the deposits are the result of precipitation from ancient ocean water, and not from elsewhere, such as the Earth's interior (for instance, from submarine volcanic activity).
The researchers believe that these deposits can provide information about ancient oceanic conditions such as pH, chemistry, and isotopic composition that has only been theorised or modelled up until now. It was stated that such information can help answer concerns about the evolution of oceans and even life on Earth.
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