Sea Salt Reveals Seawater’s Geologic History
Sea salt holds a secret hidden within its tiny crystals – droplets of ancient seawater that offer glimpses into the Earth’s geologic history. Thanks to specialized equipment obtained through a National Science Foundation grant, Mebrahtu Weldeghebriel, a postdoctoral fellow at Princeton University, and Tim Lowenstein, a Distinguished Professor of Earth Sciences at Binghamton University, were able to reconstruct changes in seawater chemistry over the past 150 million years. Their groundbreaking research sheds light on geological processes and climate changes and was published in the prestigious journal Science Advances.
Reconstructing Changes in Seawater Chemistry
The vast expanse of the ocean is not just a saline solution; it is a complex soup of different elements. While sodium and chloride are the most common elements in seawater, numerous others exist in trace amounts. Lithium, for example, plays a crucial role. Weldeghebriel and Lowenstein examined sea salt, or halite, dating back 150 million years from sedimentary basins across the globe. Inside these salt samples, they discovered tiny pockets that held remnants of ancient seawater.
Unlocking the Secrets of Ancient Seawater
The researchers devised a technique to access these minuscule droplets. By using laser technology, they drilled holes into the salt crystals, revealing the tiny pockets. They then employed a mass spectrometer to analyze the different trace elements present. Their specific focus was on lithium concentrations. Over the past 150 million years, they observed a seven-fold decrease in lithium levels, accompanied by an increase in magnesium to calcium ratios.
The Puzzle Unraveled
But what caused these long-term variations in seawater composition? The answer to this question has been the subject of debate for the past two decades. Weldeghebriel and Lowenstein proposed that the decline in lithium concentration is primarily linked to reduced production of oceanic crust and decreased seafloor hydrothermal activity. These phenomena are influenced by the movements of tectonic plates. Over the past 150 million years, a slowdown in plate activity resulted in a reduced amount of lithium being added to the ocean. This, in turn, led to a decreased release of carbon dioxide into the atmosphere, contributing to global cooling and the onset of the present ice age. By rewinding the clock 150 million years, we are transported to a warmer Earth with more carbon dioxide in the atmosphere and higher levels of lithium in the sea.
The Interconnectedness of the Oceans and Atmosphere
The research conducted by Weldeghebriel and Lowenstein not only enhances our understanding of the chemistry of ancient oceans but also highlights how the movement of tectonic plates influences the composition of Earth’s hydrosphere and atmosphere. These chemical changes have significant implications for biology as well, particularly for marine creatures that build their shells using calcium carbonate. This study underscores the close link between ocean chemistry and atmospheric chemistry, emphasizing that changes in one domain inevitably affect the other.
A Glimpse into Earth’s Complex Interplay
The research conducted by Weldeghebriel and Lowenstein marks a significant advancement in unraveling the chemical intricacies of Earth’s ancient oceans. Their findings highlight the profound impact of tectonic plate movements on the Earth’s systems and lay the groundwork for further investigations into the interconnectedness of our planet. By understanding the intricate interplay between the oceans, atmosphere, and geologic processes, scientists can gain invaluable insights into the past, present, and future of our planet.