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.

When Did Life Likely Emerge on Earth in an RNA‐First Process?

“…These primary precursors include hydrogen cyanide (HCN), cyanamide (H 2 NCN), cyanoacetylene (HCCCN), cyanogen (NCCN), ammonia (NH 3 ), and cyanic acid (HCNO). Further, they all assume that these (or their downstream products) avoided dilution into a global ocean, perhaps by adsorbing on solids, or by delivery to sub‐aerial land with a constrained aquifer …”

Ribose Selected as Precursor to Life

“…We do not know how fast/slow these transitions could have been because we fundamentally do not understand them yet. According to the recent view, life on Earth came into being through chemical evolution by producing increasingly complex molecules and yielding a molecule with the properties of information storage and replication prone to mutations (Gilbert, 1986;Bada and Korenaga, 2018). Nevertheless, the critical chemical reactions yielding the first informational macromolecule have yet to be clarified.…”

Probable Cold and Alkaline Surface Environment of the Hadean Earth Caused by Impact Ejecta Weathering

“…Cold conditions in the Hadean and moderate levels of are favorable for hypotheses of an origin of life on land. Lakes on volcanic islands have been proposed as sites for the origin of life (Bada & Korenaga, ). Such environments readily overcome the “concentration problem” for prebiotic chemistry, in which reactants must be sufficiently concentrated to drive reactions, because lakes can evaporate or, in a cold environment, lakes can freeze and concentrate solutes in residual water.…”