Ancient rocks, found in the crystalline basement of continents, are typically composed of basic and ultrabasic igneous rocks. These have undergone intense metamorphism, transforming into chlorite- and amphibole-rich metamorphic rocks known as greenstones. For instance, in 1973, a granitic gneiss with an isotopic age of approximately 3.8 billion years was discovered in West Greenland. In 1979, Bayu and colleagues dated gneiss from the central Bobolin belt in South Africa to around 3.9 billion years old. In northern Canada, the Acasta Gneiss represents one of the best-preserved ancient crustal remnants. Radiometric dating has revealed that this rock is nearly 4 billion years old, suggesting that some continental materials had already formed hundreds of millions of years after Earth's formation. This discovery provides critical insights into the early development of Earth's crust. More recently, scientists uncovered some of the oldest rocks in western Australia. Zircon crystals within these rocks, analyzed through isotope techniques, suggest their age ranges between 4.3 and 4.4 billion years. Based on these findings, it is inferred that by this time, Earth already had continents and oceans. This challenges previous assumptions that the early Earth was entirely molten. Instead, it may have cooled enough to form a solid surface and liquid oceans within 200 to 300 million years of its formation. The differentiation of Earth’s layers might have been completed as early as 4.4 billion years ago. In China, the oldest known rock is the granitic gneiss found in the eastern part of the country. Inclusions within this rock have been dated to about 3.5 billion years old, offering further evidence of early crustal evolution on our planet. Swim Spa,Swim Spa Inground,Swim Spa Aboveground,Outdoor Acrylic Swim Spa SpaRelax Co., Ltd. , https://www.sparelaxoutdoorspa.com