Background
The emergence of the first biopolymers and their building blocks on the early Earth is considered a key moment in the origin of life (OoL), but how life began on the prebiotic Earth from a pile of prehistoric inert chemicals (gases) is still confusing, and the search for its truth is often even more so because the full scenarios are difficult to recreate.

Over the past century, a variety of plausible OoL hypotheses have been proposed, mostly centered on (terrestrial or interstellar) chemical origin/ evolution theories, but there are still a lot of controversy and incompleteness about these hypotheses because each of them builds upon one-sided empirical data and/or certain theoretical bases. For instance, numerous theories explaining the (terrestrial) chemical OoL, such as the Metabolism-first world (FeS world), Zinc world, Thioester world, RNA world, Lipid world, and so on, had been proposed. However, each of them can only explain relatively narrow parts of whole scenarios, no convincing “one-piece” hypothesis so far can unify them, to provide complete and credible scenarios of how original life can arise from a bunch of inert chemicals on the planet.

Research Progress
In order to unify the existing hypotheses to cover the entire scenarios of OoL, Prof. Yongdong Jin at the School of Biomedical Engineering, Shenzhen University, China, has proposed the “nanozymes hypothesis” of the OoL on Earth. In the OoL hypothesis, primitive natural mineral nanozymes (MN-zymes) and their later upgraded organic small molecule hybridized nanozymes played a crucial role in the long history of the birth and evolution of life on Earth, especially in the early stage of the advent of life molecules and materials. They gradually catalyzed the generation of prehistoric small life molecules from nonliving matter, a bunch of prehistoric inert chemicals (gases), via complex chemical (and physical) processes in the main way of “inorganic photosynthesis”under primitive Earth conditions.

In the OoL hypothesis, as depicted in Fig. 1, multiple critical physical and chemical roles that natural MN-zymes may have played in the OoL on Earth, including (a) catalysis, (b) surface binding/confinement, (c) anti-UV irradiation, (d) (photo-)selection, and (e) energy flow management. By playing these multiple roles, MN-zymes not only manipulate themselves physically via light, heat, and electricity, for initiating chemical evolution of prebiotic organic molecules, but also enable informationization of energy into molecules (and entities) that can be read, written, and duplicated, all of which are necessary for the origin of living systems.

In fact, the Earth itself has the ability to gradually cultivate organic life and world from a completely all-inorganic primordial Earth environment and harsh conditions in the long history of the birth and evolution of life on Earth (akin to previous abiogenesis opinion). Within the framework of the hypothesis, the Earth is a natural “all-in-one” big and sustainable chemistry laboratory. As schematically depicted in Fig. 2, the existence of natural pressure gradients and temperature gradients at different depths and locations (from mantle to crust) of the Earth, especially at the sites of active volcanos and geothermal hot springs, provides abundant conditions for high temperature/high pressure lava reaction and hydrothermal reaction to generate the initial MN-zymes (such as metals/noble metals, metal oxides, and sulfide NPs), the methods of which are actually being widely used for artificial nanozymes syntheses nowadays in laboratories worldwide. These primordial MN-zymes (library) had iterated slowly and self-renewed (upgraded), and some have even become part of living organisms over the long history of Earth's evolution, and in turn resulted in the mineral evolution and mild change of the Earth's environment, all of which provide improved conditions for better survival and evolution of prebiotic molecules and primordial life.

In fact, naturally formed NPs of minerals are plentiful on Earth. Annually, thousands of terragrams (Tg) (1 Tg = 10¹² g) of mineral NPs on Earth move around in natural ecosystems; some of them exhibit intrinsic enzyme-like characteristics (termed MN-zymes), which are ubiquitous in the oceans, waters, atmosphere, and soils, and play critical roles in environmental biogeochemical cycles. Furthermore, multiple natural phenomena on Earth can spontaneously produce MN-zymes in more effective ways than we thought, as recently discovered that NMs can be simply formed via weathering of natural minerals spontaneously in charged water microdroplets, or under UV irradiation. In addition, the natural sunlight conditions and lightning phenomena also provide sufficient photocatalytic and electrocatalytic reaction conditions for the upgraded mass production of primordial natural nanozymes and their later organic hybrid nanozymes, and the generation of rich prebiotic molecules on the Earth's surface.

Fig. 3 depicts the presumed chemical origin route of prebiotic life on Earth under the framework of the hypothesis. It is worth noting that, among all working MN-zymes, the author believes that monolayer-protected gold NPs (AuNPs) as superior MN-zymes, though currently unthought of and severely overlooked, participated in and played key roles in family tree of MN-zymes in the OoL on Earth—which he referred to as the “Au world". In fact, AuNP, though regarded as an artificial nanozyme today, was a geologically plausible MN-zyme that exists under multiple geological conditions of the Earth. Although it may be hard for free AuNPs to exist in the original soup (since they can hardly stably exist without surface coating of organic molecules), AuNPs may survive on the surface of some deposits and can exist primarily in the (thiols/amines) monolayer-protected forms after small molecules like thiols and amines are produced (by other MN-zymes) and enriched at some sites.

Box 1 summarizes the abovementioned several key elements of the hypothesis for better understanding of the hypothesis for readers. Furthermore, to better understand basic principles of the OoL from a physical and chemical perspective, the author proposed further 4 essential elements and conditions for the natural selection and survival of life molecules regarding the OoL on Earth, as shown in Box 2 , namely, wet–dry cycling and amphiphilism, self-assembly and self-organization, catalytic and protoenzyme activity, and pairing symbiosis and stabilization.


Future Prospects
In addition to the aspect of nanozymes, the author also briefly and scientifically discussed in the review article several fundamental and key issues closely related to the theme of the OoL on Earth within the framework of the nanozymes hypothesis, such as: the water paradox and the significance of the micro-nano structure of the Earth's surface and the unique physicochemical properties of water/dry-wet alternating water environment on OoL; molecular cooperation and co-evolution in the early stage of OoL; And more physical contributions and insights on the OoL (including the chiral origin of biomolecules). The author hopes that the nanozymes hypothesis proposed in this article will help clarify the long-standing doubts and paradoxes about various hypotheses regarding the OoL on Earth and ultimately figure out its mystery, and will also contribute to stimulating research interest in nanozymes on the topic of OoL.

The complete study is accessible via DOI:0.34133/research.1025