Abstract:

The early Earth refers to the Hadean or dark ages of the Earth. The Hadean Earth is also known as the Earth of 4.56 to 4 Ga. The early Earth is a scientific frontier of Earth Science and a basic problem related to many theories on geology and geochemistry. This paper systematically integrates the early Earthrelated research advances, especially in the recent 10 years, from the professional popularization perspective. Focusing on the origins of large geological phenomena in the establishment of geological theory as the main line, this paper describes concisely the origins of the protoEarth core, protocrust, mantle convection, lithosphere, mantle heterogeneity, continental and oceanic crusts, water and atmosphere and oceans, plate tectonics, the origin of early life and others that are major frontier scientific issues of Earth Science. These problems are closely associated with some origins of the universe and elements related to origin of matter in the Earth. The protocore of the Earth occurred after a few million years at the beginning of the formation of the ProtoEarth; the last time global largescale melting event in the Earth happened at 4450 Ma; the Earths protomantle and protocore was again under homogenization; and the protocore may disappear. After 4450 Ma, the primitive core size is similar to the size of the present core. Only the liquid outer core was under cooling and its size decreased, while the solid inner core increased. Based on the earliest crustal zircon ages that are greater than 4408 Ma, and the earliest crustal age obtained from the Sm - Nd system is 4470 Ma; the formation of the crust is earlier than that of the late core. Therefore, the time of the protocrust separated from the protomantle is about 4.45 Ga. Based on the geochemical characteristics of Hf and Nd, some of the oldest zircons occurred at 4.3 Ga ago. The upper part of the primitivemantle after assimilation of the magma was cooled, which may constitute the primitive lithospheric mantle that can become the lower part of the protocrust. However, there is no differential oceanic and continental lithospheres in the original 4 billion years ago. There are three different theories for the origin of mantle convection which is most likely to occur in the event of accidental impact at 4.45 Ga. The origin of the mantle heterogeneity may be related to the mantle convection. The mantle heterogeneity happened earlier than the plate tectonics, which can be only explained by the theory of mantle plume or mantle overturn, and then it has been enhanced by the late plate tectonics. The origins of water, atmosphere and oceans are possibly earlier than the origins of continental and oceanic crust. The earliest water has the most reliable and direct evidence from the discovery of the oldest zircon oxygen isotope, suggesting that the water in the primary Earths surface is stable at 4.0 Ga. However, the records of the Earths earliest minerals remaining in the Western Australia Yilgan Craton (Mt. Narryer and Jack Hills area) is one 4.4 Ga zircon. The earliest zircon also means that the earliest felsic crust (continental crust) should occur at 4.4 Ga ago. Therefore, the origin of continental crust is far earlier than that of plate tectonics, and the mechanism of early continental crust origin is likely to be independent of the plate tectonics regime, triggered by the tectonicmagmatic processes and the three generations of magmatic differentiation processes under preplate tectonics regime that eventually led to the formation of largescale TTG (continental crust). Water is a prerequisite for the origin of life, so the origin of life on Earth should be later than 4.0 Ga, and the reliable fossil confirms that life at least originated before 3.7 Ga. Furthermore, early life may appear in the submarine hydrothermal vents. In summary, this paper briefly introduces the essences and frontiers of many academic achievements to help professional experts profoundly understand different fields of scientific frontiers and new achievements on the component, structures, evolution and dynamics of Early Earth.

Key words: early Earth, Earth core origin, ocean origin, continent crust origin, plate tectonics origin