Major biological events and fossil energy formation: On the development of energy science under the earth system framework

In geological history, one major life explosion and five mass extinction events occurred. These major biological and environmental events affected the evolution of the Earth ecosystem and controlled the formation of organic-rich strata. The life explosion occurred in Cambrian and the five mass extinction events happened at the end of Ordovician, Late Devonian, end of Permian, end of Triassic, and end of Cretaceous, respectively. They are corresponded to the formation of multiple suites of organic-rich strata globally, which are crucial to the formation, evolution and distribution of the fossil energy on Earth. China’s energy is characterized by "unlimited new energy, rich in coal but insufficient in oil and gas ", and it is determined to rely on new energy sources to achieve " energy independence " and carbon neutrality. From the perspective of the Earth system evolution, we investigate the multiple relationships between energy and Earth, energy and environment, as well as energy and human beings, and carry out comprehensive research on energy. Energy science refers to the science of studying the various energy sources formation and distribution, evaluation and selection, production and utilization, orderly replacement, development prospects, etc. in temporal and spatial scales based on the evolution of the Earth system. The connotation of energy science includes three core contents:(1) The relationship between the Earth and energy, including the formation of energy in the Earth system and the feedback of energy consumption to the Earth’s climate and environment;(2) The relationship between the Earth environment and the human beings, including the Earth environment breeding human beings and human activities transforming the earth environment;(3) The relationship between the energy and the human beings, including the development of energy technology by human beings and the progress of human society driven by energy utilization. The energy science focuses on the formation and development of fossil energy, development and orderly replacement of new energy, exploration and utilization of energy in deep earth and deep space, and energy development strategy and planning. The proposal of energy science is of great significance for improving the discipline system, promoting energy development, clarifying the development direction of energy transition, driving the carbon neutral geology research and constructing a habitable Earth.

The naked planet Earth:Most essential pre-requisite for the origin and evolution of life

Our blue planet Earth has long been regarded to carry full of nutrients for hosting life since the birth of the planet.Here we speculate the processes that led to the birth of early life on Earth and its aftermath, finally leading to the evolution of metazoans.We evaluate：（1） the source of nutrients,（2） the chemistry of primordial ocean,（3） the initial mass of ocean,and（4） the size of planet.Among the life-building nutrients,phosphorus and potassium play a key role.Only three types of rocks can serve as an adequate source of nutrients：（a） continent-forming TTG（granite）,enabling the evolution of primitive life to metazoans;（b） primordial continents carrying anorthosite with KREEP（Potassium,Rare Earth Elements, and Phosphorus） basalts,which is a key to bear life;（c） carbonatite magma,enriched in radiogenic elements such as U and Th,which can cause mutation to speed up evolution and promote the birth of new species in continental rift settings.The second important factor is ocean chemistry.The primordial ocean was extremely acidic（pH = 1-2） and enriched in halogens（CI,F and others）,S,N and metallic elements（Cd,Cu,Zn,and others）,inhibiting the birth of life.Plate tectonics cleaned up these elements which interfered with RNA.Blue ocean finally appeared in the Phanerozoic with pH = 7 through extensive interaction with surface continental crust by weathering,erosion and transportation into ocean.The initial ocean mass was also important.The birth of life and aftermath of evolution was possible in the habitable zone with 3-5 km deep ocean which was able to supply sufficient nutrients. Without a huge landmass,nutrients cannot be supplied into the ocean only by ridge-hydrothermal circulation in the Hadean.Finally,the size of the planet plays a crucial role.Cooling of massive planets is less efficient than smaller ones,so that return-flow of seawater into mantle does not occur until central stars finish their main sequence.Due to the suitable size of Earth,the dawn of Phanerozoic witnessed the initiation of return-flow of seawater into the mantle,leading to the emergence of huge landmass above sea-level,and the distribution of nutrients on a global scale.Oxygen pump also played a critical role to keep high-PO_2 in atmosphere since then,leading to the emergence of ozone layer and enabling animals and plants to invade the land. To satisfy the tight conditions to make the Earth habitable,the formation mechanism of primordial Earth is an important factor.At first,a ＇dry Earth＇ must be made through giant impact,followed by magma ocean to float nutrient-enriched primordial continents（anorthosite ＋ KREEP）.Late bombardment from asteroid belt supplied water to make 3-5 km thick ocean,and not from icy meteorites from Kuiper belt beyond cool Jupiter.It was essential to meet the above conditions that enabled the Earth as a habitable planet with evolved life forms.The tight constraints that we evaluate for birth and evolution of life on Earth would provide important guidelines for planetary scientists hunting for life in the exosolar planets.

Origin of the Earth:A proposal of new model called ABEL

The Earth was born as a dry planet without atmosphere and ocean components at 4.56 Ga,with subsequent secondary accretion of bio-elements,such as carbon（C）,hydrogen（H）,oxygen（O）,and nitrogen（N） which peaked at 4.37-4.20 Ga.This two-step formation model of the Earth we refer to as the advent of bio-elements model（ABEL Model） and the event of the advent of bio-elements（water component） as ABEL Bombardment.It is clear that the solid Earth originated from enstatite chondrite-like dry material based on the similarity in oxygen isotopic composition and among other isotopes.On the other hand,Earth＇s water derives primarily from carbonaceous chondrite material based on the hydrogen isotopic ratio.We present our ABEL model to explain this enigma between solid Earth and water,as well as secondary accretion of oxidizing bio-elements,which became a precursor to initiate metabolism to emerge life on a highly reductive planet.If ABEL Bombardment had not occurred,life never would have emerged on the Earth.Therefore,ABEL Bombardment is one of the most important events for this planet to evolve into a habitable planet.The chronology of ABEL Bombardment is informed through previous researches of the late heavy bombardment and the late veneer model.ABEL Bombardment is considered to have occurred during 4.37-4.20 Ga,which is the concept to redefine the standard late heavy bombardment and the late veneer models.Also,ABEL Bombardment is the trigger of the transition from stagnant lid tectonics to plate tectonics on this planet because of the injection of volatiles into the initial dry Earth.

The oxygen cycle and a habitable Earth

As an important contributor to the habitability of our planet, the oxygen cycle is interconnected with the emergence and evolution of complex life and is also the basis to establish Earth system science. Investigating the global oxygen cycle provides valuable information on the evolution of the Earth system, the habitability of our planet in the geologic past, and the future of human life. Numerous investigations have expanded our knowledge of the oxygen cycle in the fields of geology,geochemistry, geobiology, and atmospheric science. However, these studies were conducted separately, which has led to onesided understandings of this critical scientific issue and an incomplete synthesis of the interactions between the different spheres of the Earth system. This review presents a five-sphere coupled model of the Earth system and clarifies the core position of the oxygen cycle in Earth system science. Based on previous research, this review comprehensively summarizes the evolution of the oxygen cycle in geological time, with a special focus on the Great Oxidation Event(GOE) and the mass extinctions, as well as the possible connections between the oxygen content and biological evolution. The possible links between the oxygen cycle and biodiversity in geologic history have profound implications for exploring the habitability of Earth in history and guiding the future of humanity. Since the Anthropocene, anthropogenic activities have gradually steered the Earth system away from its established trajectory and had a powerful impact on the oxygen cycle. The human-induced disturbance of the global oxygen cycle, if not controlled, could greatly reduce the habitability of our planet.