A comprehensive understanding of the inception and degradation of our planet’s continental lithosphere during the Archean eon is paramount for deciphering early oceanic geochemistry, the trajectory of biosphere development, and the initiation of plate tectonic activity.
An artistic conception of the early Earth. Image credit: Simone Marchi / NASA.
Following the consolidation of terrestrial landmasses through dynamic geological mechanisms such as plate tectonics, the process of weathering commences, contributing essential minerals and vital nutrients to oceanic bodies.
Evidence of these nutrient contributions is meticulously preserved within the geological strata of ancient rock formations.
Prior investigations relied on strontium isotope analyses of marine carbonate deposits; however, such rock sequences are typically scarce or significantly altered in geological samples predating 3 billion years.
A novel methodology for tracing the initial appearance of ancient terrestrial rocks has been pioneered by Desiree Roerdink, a geochemist at the University of Bergen, and her research collaborators. This innovative approach utilizes a distinct mineral, barite, as its analytical focus.
Barite precipitates from a confluence of sulfate ions derived from seawater and barium originating from hydrothermal geological features.
The structural integrity of this mineral encapsulates a durable historical record of oceanic chemical conditions, proving invaluable for reconstructing paleoenvironmental settings.
“The elemental composition of a barite sample we retrieve from the field today, having been part of Earth for 3.5 billion years, remains identical to its state at the moment of its original precipitation,” stated Dr. Roerdink.
“Consequently, it serves as an exceptionally reliable proxy for examining geological processes that occurred on the primordial Earth.”
Dr. Roerdink and her research team conducted analyses on six distinct barite deposits spanning three different continents, with ages ranging approximately from 3.2 to 3.5 billion years.
By determining the strontium isotope ratios within these barite samples, they were able to deduce the timeframe during which weathered continental strata were transported to the oceans and subsequently incorporated into the barite structure.
The newly acquired data indicates that the onset of terrestrial weathering occurred approximately 3.7 billion years ago, signifying an advancement of around 500 million years beyond previously established estimates.
“This represents an immense temporal span, carrying profound implications for our understanding of how life evolved,” Dr. Roerdink commented.
“Current scientific paradigms often posit the origins of life within deep-sea, hydrothermal environments; however, the biosphere’s evolution is inherently complex.”
“It remains uncertain whether life could have concurrently emerged on land, but such a possibility necessitates the prior existence of landmasses.”
“Furthermore, the emergence of terrestrial continents provides insights into the dynamics of plate tectonics and the nascent development of a geodynamically active Earth.”
“The formation of land requires specific geological processes to create continental crust, distinct chemically from the oceanic crust.”
The findings of this research were formally presented by the investigators at the EGU General Assembly 2021.
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D. Roerdink et al. 2021. The emergence of subaerial crust and onset of weathering 3.7 billion years ago. EGU21-4701; doi: 10.5194/egusphere-egu21-4701
