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rom interstellar stone to terrestrial treasure: what is the amazing journey of the Hadean zircon
On our planet, there is a precious mineral called Hadean zircon, which is a survivor of the earliest rock material on Earth and was formed in the Hadean period about 4 billion years ago. These tiny crystals, which resist chemical changes and occur in most igneous and metamorphic rocks, are important materials scientists use for radioactive dating studies.
The rarity and uniqueness of Hadean zircon make it a key to understanding early Earth.
However, Hadean zircon is present at extremely low rates around the globe due to recycling effects of plate tectonics. When surface rocks are buried deep inside the Earth, they recrystallize or melt due to the intense heat. Scientists have a relatively comprehensive record of Hadean zircons in the Jack Hills region of Australia, where the zircons come from metamorphic sediments deposited about 3 billion years ago, but are older than the rocks that surround them.
Through in-depth investigations into the properties of Hadean zircon crystals, scientists have gained valuable information about the early history of the Earth and its geological processes, and have proposed a variety of geological models based on these properties.
Background
ImportanceLearn more about Earth's history
The geological history of the Hadean Epoch remains largely unknown due to the lack of a rock record beyond 4.02 billion years. Most scientists agree that plate tectonic plates have melted almost all of Earth's crust, but some tiny fragments of it have survived, which is an important reason why the rare Hadean zircon is found in younger host rocks.
The study of Hadean zircons is crucial to revealing the early geological conditions of the Earth.
Scientific Contributions
Due to the lack of strong evidence to depict the actual environment of the early Earth, many models have been generated to explain the history of the early Earth. High rates of heat generation and shock flows indicate that continental crust was not present, which is very different from present-day processes. Rapid advances in computational geophysics and planetary science have paved the way for exploring this new area of knowledge, limited by changing analytical methods and a large lack of data.
Rarity
Of the zircons detected worldwide, less than 1% are older than 4 billion years. The number of zircons older than 4 billion years found at Jack Hills shows an unusually high rate for the region. Using uranium-lead dating (U-Pb) techniques, the researchers found that of more than 200,000 detrital zircons that had been U-Pb dated, only 3% were older than 4 billion years.
Type
Depending on the different uranium contents and trace element concentrations, Hadean zircon can be divided into four categories, namely lunar and meteorite zircon, sedimentary grain zircon, kimberlite zircon and oceanic crust zircon. Hadean zircon on Earth and zircon in outer space have significant differences in crystallization temperature and oxygen isotope characteristics, providing clues to understanding the formation process of these crystals.
Nature
The Hadean zircon samples at Jack Hills were analyzed not only for their abundance, but also for their distribution of ages and various chemical signatures.
U-Pb dating technology can not only reveal the age of zircon, but also provide valuable information on the evolution of the earth's crust.
By analyzing the isotope geochemistry and mineral inclusions of Hadean zircons, scientists were able to verify their formation environment and evolution processes. The study of Hadean zircon provides a window into our understanding of the early Earth.
Analysis Methods
With the advancement of technology, isotope analysis and uranium-toluene-lead dating by Ion microprobe have become important methods for studying Hadean zircon. These techniques can provide high-precision data at the microscopic level. In addition, electron microanalysis is also used to study the chemical composition of inclusions in zircon to further reveal their causes.
Mechanism of formation of Hadean Jack Hills zircon
Based on current scientific models, most scholars generally accept the theory of plate tectonics, which states that the existing earth's crust was generated through various geological processes. For the formation of Hadean zircon, a large number of studies point to the humid environment of the early Earth and propose different thermal history models and continental growth models. These new discoveries not only challenge previous views of the early Earth, but also promote the depth and breadth of related research.
As we explore these mysterious Hadean zircons, we can't help but ask, can they give us more clues about the origin of life in the universe?
