Hills on the Western side of Australia reveal facts on the natural turbulence that gave birth to the continent Earth as it looked now. Peck, Simon Wilde at the Curtin Institute of Technology in Australia; John Valley at the University of Wisconsin, Madison; and Colin Graham of the University of Edinburgh in the United Kingdom discovered 4. 4 billion years old tiny crystals known as zircons, which are considered as the oldest dated minerals of terrestrial origin. From these crystals, scientists are trying to frame a portrait of the Earth how it looked like 4. 4 billion years old. (NASA Astrobiology Institute 2001)
Those Zircons weigh approximately 250 microns in width, which is approximately considered as less than one one-hundredth of an inch. As said by Peck, “The zircon is ‘our earliest record of the earliest crust’ on Earth. Zircons deposited in ancient stream show that the continents, water, oceans and environments and other microbial life came into existence some 4. 3 to some 4. 4 billion years ago. (Clancy, Brack and Horneck, 2005) The Zircons contain the traces of uranium and thorium, which proved to be useful for dating of rocks. Zircons are defiant to weathering, erosion, and re-melting.
It is believed that Zircons came into existence only soon after the formation of the earth, when water interacted with rocks and this amalgamation can have occurred only in three ways: firstly when there is an exchange of water with minerals in rocks, secondly when crystals are formed and thirdly when the veins in minerals are deposited. (NASA Astrobiology Institute 2001) With the interaction with water, rocks raised but later lowered due to certain bombardment by meteorites and with this there was a formation of zircons within molten granite that was getting cooler which in turn began to be formed into solid rock. NASA Astrobiology Institute 2001) It is said that the granite, which was laden with zircons, was pushed open and later battered.
Though the granite broke into pieces, but zircons got scattered into places and finally got placed in sandy Australian stream sediments, which turned into hard rocks. Studies pinpointed to the fact such granites have never been found but these ancient zircons are the testament to the presence of granites as said by Geologist Sam Bowring of the Massachusetts Institute of Technology. “The fact you have a 4. 4-billion-year-old zircon from granite suggests there had to be the rock of the continental crust. (NASA Astrobiology Institute 2001) Zircon discoveries motivated several scientists to unravel mysteries of our mother Earth. The surface of each zircon is greatly rough, which implies that they must have traveled greater distances from their source rock. From zircon only, scientists can predict the longevity of their existence i. e. individual crystals of zircons can be dated once extracted from their source rock, as they are ideal timekeepers. Uranium, rare earth elements and other impurities like lead are often contained in these zircons. “The uranium-lead clock starts ticking as soon as the zircon crystallizes.
Thus, the ratio of lead to uranium increases with the age of the crystal. Scientists can reliably determine the age of an undamaged zircon within 1 percent accuracy, which for the early earth is about plus or minus 40 million years”. (Valley 2005) Instruments called ion microprobes were used to date and analyze the specific parts of single crystal. The dating of zircons could became possible only in 1980 when William Compston and his colleagues at the Australian National University in Canberra invented a special kind of ion microprobe named SHRIMP.
As the most zircons are almost invisible to naked eye, a beam of ions is fired so narrowly focused by the ion microprobe that small number of atoms can be blasted off any targeted part of a zircon’s surface. Then the composition of those atoms is measured by a mass spectrometer by comparing their masses to determine the age of the crystal. If ratio of lead is more than the uranium due to the constant decay of radioactive uranium, it means that the crystal is older. It was in 1986 when Jack Hills zircons were first dated by a Compston’s group (Robert T.
Pidgeon, John Baxter and Robert T. Pidgeon) at Curtin University of Technology in Australia. (Valley 2005) Discovery of Zircons from the Jack Hills of Western Australia changed the perception of scientists about the early history of the earth. They found that temperatures had cooled to the 100-degree Centigrade range 4. 4 billion years ago, which implies that early Earth to be far different than imagined. John Valley, a geologist at UW-Madison, says, “This is an astounding thing to find for 4. 4 billion years ago. At that time, the Earth’s surface should have been a magma ocean.
Conventional wisdom would not have predicted a low-temperature environment. These results may indicate that the Earth cooled faster than anyone thought. ” (ScienceDaily 2001) Scientists held the view of infant Earth as a swirling ball of molten metal and rock shortly after it first formed 4. 5 to 4. 6 billion years ago. They believed that Earth took a long time about 700 million years to cool from a dense and steamy atmosphere. Massive meteorites struck Earth blasting craters of the size about 1,000 kilometers in diameter for hundreds of millions of years.
Also, the decay of radioactive elements produced heat deep underground six times greater than what is produced today. (Valley 2005) Oceans of magma roiled the surface of the earth due to the repeated collisions with massive boulders, orbiting the sun. The surface got scorched i. e. got shattered, melted and vaporized on contact with each impact, which took at the rate of 75 times the speed of sound. (Valley 2005) It is believed that Mars-size object slammed into the Earth about 4. 45 billion years ago and thus moon was created when pieces of Earth blasted into space due to the collision. Science Daily 2001) Scientists assume that these fiery hellish conditions continued for more than 500 million years that is why they named this era as Hadean. Geologist William Peck said that a new view of the early Earth is given by these zircons when Earth cooled quickly “after gas and dust in the newborn solar system congealed to form planets. ” (NASA Astrobiology Institute 2001)
Studies also indicate that continents and water really existed early which were eliminated by meteorites and thus all the records also got obliterated except these zircons. This view is in sharp contrast to the old view, which held that stabilizing of Earth i. . formation of oceans and continents was a slow process. The hellish conditions, which prevailed earlier, must have erased any life living there. Now these zircons exhibit the existence of continents and oceans 4. 3 billion to 4. 4 billion years ago and the life could have emerged 400 million years earlier than recorded previously. Peck viewed that life could have arisen many times but would have been destroyed by the meteorites and life could have stabilized only when the meteorites had tapered off. Also, there was water on the earth 4. 3 billion to 4. billion years ago was confirmed when the zircons were analyzed for oxygen isotopes and isotope of oxygen-18 was found as compared to oxygen-16. To this Peck said “we know there was liquid water at some point before 4. 4 billion years ago” (NASA Astrobiology Institute 2001) and this liquid water must have collected somewhere to form oceans and also it is viewed that oceans existed because water is needed to make continents. Peck is of the view that before the oceans were there, giant plates of Earth’s crust could have moved and collided as a result these huge blocks of rocks would have dived downward due to the process known as subduction.
Also, the rocks could not have melted without oceans to form granite, a type of continental rock. If oceans were there then the hydrated lava erupting from undersea volcanoes would have reacted with seawater. A new seafloor would have formed with the cooling of lava, which got subducted afterwards. The melting point of the sinking rocks got lowered due to the presence of water trapped in minerals resulting in the volcanic eruptions, which produced chains of islands, made of granitic rocks.
It is assumed that clumping together of these types of island arcs formed continents. According to Geologist Stephen Mojzsis, life could have existed on Earth 4. 3 billion years ago as suggested by zircons as three essential factors for the emergence of life i. e. energy, organic matter coming from atmospheric reactions and comets and thirdly liquid water according to zircons were present there. (NASA Astrobiology Institute 2001) Mojzsis also said that according to findings by two research groups, “liquid water stabilizes early on Earth-type planets. (NASA Astrobiology Institute 2001) This means that conditions conducive to life can develop faster and more easily than previously thought and thus the likelihood of finding life elsewhere in universe increases. The research to unravel the hidden mystery of the Earth i. e. to discover new insights about the early crust and early Earth is still being continued by the scientists worldwide, as the discovery of zircons have added new dimensions to their research by refuting the claims made by scientists about the early earth.