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A time warp in Earth history: How does the Hadean zircon reshape our understanding of early Earth?
In the long history of the earth, Hadean zircon, as an existing mineral in the early earth, is of great significance to our understanding of the geological conditions of that period. The Hadean Zircon is the oldest known crustal material from Earth's early days, dating to approximately 4 billion years ago, providing a window into this period. With the deepening of scientific research, the secrets of the earth's past revealed by Hadean zircon gradually surfaced.
Background
Importance
The geological history of Hadean eon is not fully understood, mainly due to the lack of rock records that are more than 4.02 billion years old.
Current research shows that Earth's plate movement mechanism has melted nearly all of the Earth's crust. However, there are still tiny parts of the crust that have not been melted, including rare Hadean zircon grains that were recently discovered in the geological formation. Studies of these Hadean zircon could provide evidence of the geophysical conditions of the early Earth.
Scientific Contribution
Due to the lack of strong evidence describing the true environment of the early Earth, various models have been proposed to explain the early Earth's history.
The high values of heat production and flux in the Hadean zircon indicate that no continental crust existed at that time, which is quite different from modern geological processes. In the absence of large amounts of unallocated data, computation in geophysics and planetary science is rapidly evolving to explore this new area of knowledge.
Rarity
Globally, the probability of discovery of zircon that is more than 4 billion years old is extremely low, probably no more than 1%.
The high discovery rate in Jack Hills indicates its rarity is much higher than in other locations. Research shows that only 3% of more than 200,000 detrital zircon particles have been confirmed to be older than 4 billion years by U-Pb analysis.
Type
Hadean zircon can be divided into four clusters based on different uranium and trace element concentrations:
- Moon and meteorite zircon
- Deposited particle zircon
- Kimberlite zircon
- Ocean crust zircon
The crystallization temperatures of most of these zircon are between 600 and 780°C. There are also significant differences in oxygen isotopes between the terrestrial Hadean zircon and the zircon in outer space.
Features
Extracting Jack Hills zircon for analysis involves multiple chemical and radioisotope determinations. The research results show that the age combination of these zircon particles shows a bimodal distribution, mainly between 3.4 billion years and 4.1 billion years.
Isotope geochemistry
Stable isotope data show that the original host rock to which zircon is associated was largely material that formed near the Earth's surface.
Through these isotope data, researchers were able to reconstruct the environment in which Hadean zircon formed and infer the diversity and complexity of the early Earth environment.
Analytical methods
Ion microprobe analysis
SIMS and uranium-thorium-lead (U-Th-Pb) dating are common methods for measuring isotopes. The high-resolution data from these techniques provide sufficient support for analyzing the formation process of zircon.
Electron microprobe analysis
The JNEL 8600 Electron Microprobe Analyzer (EPMA) used to study the interior of minerals can analyze the chemical composition of zircon and estimate the abundance of elements. Through such research, scientists can unravel the origin of zircon and how they are formed.
Generation mechanism of Hadean Jack Hills zircons
Research on Hadean rock records shows that the early Earth was not a scorching environment as conventional wisdom had it.
Scientists believe that the plate tectonics theory can explain the creation of the Hadean Jack Hills zircons, which shows the potential of ancient crustal formation mechanisms.
As research progresses, Hadean zircon will undoubtedly provide valuable evidence for describing the early history of the Earth. However, is this evidence enough to completely change our understanding of the formation and evolution of the Earth?
