Kanada’da 4,28 Milyar Yaşlı Kayaç Bulundu
4,28 milyar yaşıyla dünyanın en eski kaya kütlesi Kanada’da bulundu. Science dergisinin son sayısında yer alan makaleye* göre Kanada’nın Quebec eyaletinin kuzeyinde Hudson körfezi kıyılarında ”Nuvvuagittuq yeşil kuşağı” olarak adlandırılan bölgesinde bulunan kaya kütlesi yaklaşık 10 kilometre karelik bir alana yayılmış durumda ve pembe-kahverengi renkleriyle çok güzel bir görünüme sahip.
Dünyanın yaşının 4,57 milyar yıl olduğu dikkate alındığında bu eski kaya kütlesinin neredeyse dünyanın oluşumundan kısa bir süre sonra (290 milyon yıl sonra) şekillendiğini düşünmek mümkün. Bu kaya kütlesi dünyanın ilk soğumaya başladığı dönemlerden kalma. Daha önce de 4,03 milyar yaşında olduğu saptanan en eski kaya kütlesi yine Kanada’da bulunmuştu.
Earth’s oldest known rock is composed of the mineral amphibole, which contains abundant garnet, seen as large round “spots” in the rock. Credit: Jonathan O’Neil.
(McGill) McGill Researchers Find Oldest Rocks On Earth
Discovery of rocks as old as 4.28 billion years pushes back age of most ancient remnant of Earth’s crust by 300 million years.
McGill University researchers have discovered the oldest rocks on Earth – a discovery which sheds more light on our planet’s mysterious beginnings. These rocks, known as “faux-amphibolites”, may be remnants of a portion of Earth’s primordial crust – the first crust that formed at the surface of our planet. The ancient rocks were found in Northern Quebec, along the Hudson’s Bay coast, 40 km south of Inukjuak in an area known as the Nuvvuagittuq greenstone belt. Their results will be published in the September 26 issue of the journal Science.
The discovery was made by Jonathan O’Neil, a Ph.D. candidate at McGill’s Department of Earth and Planetary Sciences, Richard W. Carlson, a researcher at the Carnegie Institution for Science in Washington, D.C., Don Francis, a McGill professor in the Department of Earth and Planetary Sciences, and Ross K. Stevenson, a professor at the Université du Québec à Montréal (UQAM).
O’Neil and colleagues estimated the age of the rocks using isotopic dating, which analyzes the decay of the radioactive element neodymium-142 contained within them. This technique can only be used to date rocks roughly 4.1 billion years old or older; this is the first time it has ever been used to date terrestrial rocks, because nothing this old has ever been discovered before.
The data from these findings will give researchers a new window on the early separation of Earth’s mantle from the crust in the Hadean Era, said O’Neil.
“Our discovery not only opens the door to further unlock the secrets of the Earth’s beginnings,” he continued. “Geologists now have a new playground to explore how and when life began, what the atmosphere may have looked like, and when the first continent formed.”
* Geologists report the discovery of rock in northern Quebec on Hudson Bay that records the existence of the earliest crust. The Canadian rock may also be the oldest known rock by 300 million years.
Geologists Find Vestige of Early Earth-Maybe World’s Oldest Rock, 2008. 26 September, Science, V. 321, N. 5897, pp. 1828-1831.
Neodymium-142 Evidence for Hadean Mafic Crust
Neodymium-142 data for rocks from the Nuvvuagittuq greenstone belt in northern Quebec, Canada, show that some rock types have lower 142Nd/144Nd ratios than the terrestrial standard (142Nd = –0.07 to –0.15). Within a mafic amphibolite unit, 142Nd/144Nd ratios correlate positively with Sm/Nd ratios and produce a 146Sm-142Nd isochron with an age of 4280 million (+53, -81) years. These rocks thus sample incompatible-element-enriched material formed shortly after Earth formation and may represent the oldest preserved crustal section on Earth.
Bu haber, AA ve McGill Üniversitesi sitelerinden derlenmiştir.
Bunu okuyan, bunları da okudu..
Yorumunuz mu var?
Yakın Takip
Güvenli Yaşam
Evrim 101 (~Türkçe)
