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

Abstract

How life began on Earth is still largely shrouded in mystery. One of the central ideas for various origins of life scenarios is Darwin's "warm little pond". In these small bodies of water, simple prebiotic compounds such as amino acids, nucleobases, and so on, were produced from reagents such as hydrogen cyanide and aldehydes/ketones. These simple prebiotic compounds underwent further reactions, producing more complex molecules. The process of chemical evolution would have produced increasingly complex molecules, eventually yielding a molecule with the properties of information storage and replication prone to random mutations, the hallmark of both the origin of life and evolution. However, there is one problematic issue with this scenario: On the Earth >3.5 Gyr ago there would have likely been no exposed continental crust above sea level. The only land areas that protruded out of the oceans would have been associated with hotspot volcanic islands, such as the Hawaiian island chain today. On these long-lived islands, in association with reduced gas-rich eruptions accompanied by intense volcanic lightning, prebiotic reagents would have been produced that accumulated in warm or cool little ponds and lakes on the volcano flanks. During seasonal wet⁻dry cycles, molecules with increasing complexity could have been produced. These islands would have thus been the most likely places for chemical evolution and the processes associated with the origin of life. The islands would eventually be eroded away and their chemical evolution products would have been released into the oceans where Darwinian evolution ultimately produced the biochemistry associated with all life on Earth today.

Keywords: continental crust; exposed land; prebiotic chemistry; volcanic islands; volcanic lightning.

Figure 1

Likely evolution of continental area on the Earth based on continental freeboard modeling: exposed above sea level (solid) and total (dashed) (based on Figure 4d in ref. [20]).

Figure 2

(a) Hotspot island formation in the stagnant lid regime of mantle convection. An island considerably larger than a typical hotspot island today can be constructed by continuous magma input from a stationary mantle plume. (b) Two contrasting fates of hotspot islands in early plate tectonics. Those formed on young ocean floor would have subsided as quickly as present-day hotspot islands, whereas those on older ocean floor could have been subaerial on a longer time scale because of subdued seafloor subsidence. See text for further explanation.

Figure 3

(a) Volcanic lightning associated with an eruption of the Colima Volcano in 2015 (photo credit: Sergio Tapiro); (b) a nearby “warm little pond” (WLP) on a volcano flank (Courtesy Ben K. D. Pearce).

Figure 4

Aerial view taken in 1965 of ice-covered Lake Waiau in the Pu‘u Waiau cinder cone near the summit of the Mauna Kea volcano on the island of Hawai‘i (USGS Library, Denver; Photo KPA-N183].