Scientists discover 600-million-old ocean water in Himalayan mineral deposits

Himalayan magnesite is a rare exception

One of the critical events in Earth history, the Snowball Earth glaciation, during which most of the planet was covered with thick sheets of ice, was followed by another event. The Second Great Oxygenation Event, during which oxygen level in the Earth’s atmosphere increased manifolds and led to the evolution of complex life forms.

This research directly links the two events, given that the deposits the scientists found reveal that sedimentary basins were deprived of calcium for an extended period during the Snowball Earth glaciation, probably due to low riverine input as a product of the changing weathering.

“Minerals precipitated from seawater, however, have the potential to preserve evidence of their paleo-oceans. Magmatic, metamorphic, and hydrothermal fluids are commonly trapped in rock-forming minerals. Still, inclusions of paleo-ocean are rarely known because carbonates, the most common marine precipitate, are mostly too fine-grained, readily recrystallized, and chemically altered,” the researchers noted. 

“We have found a time capsule for paleo oceans. We don’t know much about past oceans. How different or similar were they compared to present-day oceans? Were they more acidic or basic, nutrient-rich or deficient, warm or cold, and what was their chemical and isotopic composition? Such insights could also provide clues about the Earth’s past climate, and this information can be useful for climate modeling,” said Prakash Chandra Arya, first author of the study, in an interview with The Hindu.

The research is a joint effort between researchers from the Indian Institute of Science in Bengaluru and Niigata University in Japan.

The study was published in Precambrian Research.

Study abstract:

The widespread glaciation (∼750–580 Ma) of the late Neoproterozoic Snowball Earth and the subsequent (∼630–551 Ma) oxygenation of the oceans and atmosphere were critical factors in microbial evolution and the following ∼540–520 Ma explosion of complex life forms in the Cambrian. However, the underlying mechanisms that link these processes are still unclear due to poorly preserved fossil records and the tectonic destruction of the paleo-oceans, limiting our understanding of the Neoproterozoic Earth, a key time when unicellular life evolved into complex forms. Droplets of Neoproterozoic oceanwater and freshwater trapped in Himalayan crystalline magnesite (MgCO3) show that sedimentary basins were deprived of calcium for an extended period during the Snowball Earth glaciation, probably due to low riverine input of the dissolved products of weathering. Protracted precipitation of calcite-dolomite in a closed basin, now exposed in Kumaun Himalayas, Uttarakhand (India), decreased the Ca/Mg ratio in the seawater. This fall in the Ca/Mg ratio—initiated magnesite precipitation and increased the basin's oligotrophy (nutrition deficiency). The slow-growing photosynthetic cyanobacterial stromatolites could thrive in such oligotrophic conditions. The same is reflected in the field, i.e., the appearance of stromatolites towards the end of dolomite formation and their population expansion in the overlying magnesite beds. Continued magnesite precipitation in a closed basin, driven by positive feedback, resulted in high photosynthetic oxygen production, conceivably triggering the Neoproterozoic Oxygenation Event and stimulating Cambrian Explosion.