Rapid emergence of subaerial landmasses and onset of a modern hydrologic cycle 2.5 billion years ago

Abstract

The history of the growth of continental crust is uncertain, and several different models that involve a gradual, decelerating, or stepwise process have been proposed. Even more uncertain is the timing and the secular trend of the emergence of most landmasses above the sea (subaerial landmasses), with estimates ranging from about one billion to three billion years ago. The area of emerged crust influences global climate feedbacks and the supply of nutrients to the oceans , and therefore connects Earth's crustal evolution to surface environmental conditions. Here we use the triple-oxygen-isotope composition of shales from all continents, spanning 3.7 billion years, to provide constraints on the emergence of continents over time. Our measurements show a stepwise total decrease of 0.08 per mille in the average triple-oxygen-isotope value of shales across the Archaean-Proterozoic boundary. We suggest that our data are best explained by a shift in the nature of water-rock interactions, from near-coastal in the Archaean era to predominantly continental in the Proterozoic, accompanied by a decrease in average surface temperatures. We propose that this shift may have coincided with the onset of a modern hydrological cycle owing to the rapid emergence of continental crust with near-modern average elevation and aerial extent roughly 2.5 billion years ago.

Exposed Areas Above Sea Level on Earth >3.5 Gyr Ago: Implications for Prebiotic and Primitive Biotic Chemistry

“…Geological records for exposed continents are rare for >3 Gyr ago. Spatially expansive exposure horizons can be identified in the Precambrian sedimentary record only after ~3 Gyr ago [20], and this is consistent with the abundant occurrence of submarine flood basalt magmatism in the Archean [21] and with the oxygen isotope record of shales [22]. Recent modeling of continental freeboard indicates that plate tectonics results in the net water flux from the oceans to the mantle at the rate of 3–4.5 × 10 14 g/yr [20], and such positive net water influx has also been suggested by the global water cycle [23].…”

Early Archean origin of Photosystem II

“…The development of water oxidation would have opened up the way to faster photosynthetic rates, spurring on gross primary production rates, later in the Archean, with the concomitant need for increases in nitrogen fixation. In consequence, if water oxidation originated at an early stage during the evolutionary history of life other geological processes should have delayed the oxygenation of the planet until the Great Oxidation Event (Bindeman et al., ; Smit & Mezger, ).…”

Large influence of dust on the Precambrian climate

“…That means, the effect of dust on deep-time paleo-climate was enormous and should always be considered when simulating early Earth climatic conditions as long as large area of continents have formed. Recent studies showed that the area of continents had probably not been much smaller than that of present day since 2.5 billion years ago 35,36 . Whether dust has promoted the initiation of Neoproterozoic snowball Earth or not is uncertain because it can lower the surface albedo and warm the climate when there is a large amount of sea ice (such as in a near snowball state); this effect may overwhelm its cooling effect and warrants further investigation.…”