In August, the geologist Matt Jackson with his wife and four-year-old daughter moved from California to the fjords of Northwest Iceland, broke up the camp and became day time to wander the cliffs and rocky slopes in search of a little olive green stones are called olivine.
Jackson, a cheerful young Professor from the University of California, Santa Barbara with a shirt with pearl buttons and worn shorts for two years studied the best hunting grounds of the Icelandic fjords. While referring to brief notes in the legacy of other geologists ‘ field log, on the day he passed 10-15 miles past countless sheep and random farmers. “All their lives they lived in those beautiful fjords,” he said. “They look at black layered rocks, and I tell them that each of them is the eruption of volcanic lava. They’re just in shock!” He laughed. “And I’m more shocked by the fact that they never understood it!”
Olivine broke through the surface of the Earth, composed of lava flow 10 to 17 million years ago. Jackson, like many geologists believed that the source of the eruptions was the Icelandic mantle plume is a hypothetical thermal solid rocks deep in the Earth according to the principle of the balls in a lava lamp. This plume, if it exists, causes would now work active volcanoes in Central Iceland. In the past he would have risen to the surface here, in the fjords, before the part of the earth’s crust, which is Iceland, moved to the North-West.
According to other contemporary studies in this region, the olivine could occur from the ancient reservoir of minerals at the base of the Icelandic mantle plume, which over billions of years never mingled with the rest of the Earth. Jackson hoped that the collected samples are some sort of chemical information from this reservoir and prove that he was formed in the era of the infancy of our planet, which until recently was considered inaccessible to science period.
After returning to California, he sent his samples to Richard Walker to find out what that information is. Walker, a geochemist from the University of Maryland, is engaged in processing of olivine to determine the concentration therein of a chemical isotope tungsten-182 compared to the more common isotope of tungsten-184. If Jackson is right, the samples will join the growing collection of stones that have absolutely amazing abnormal ratio of isotopes of tungsten. These tungsten anomalies reflect the processes that could happen only during the first 50 million years of the Solar system — the period of formation, which, as was long assumed, has been erased from the annals of geochemical destructive collisions that the Earth and mix its contents.
The anomaly “gives us information on some of the earliest processes of the planet Earth,” said Walker. “It’s the universe, alternative to the one with which the last 50 years worked geochemists”.
Such discoveries are pushing geologists like Jackson in search of new clues to the origin of the Earth and modern mechanisms for its operation. Both modern and early Earth has been insufficiently studied. Many questions remain unanswered, starting with how are volcanoes and whether there are plumes before any oceans and continents and what is the nature and origin of giant structures colloquially called “clusters” detected by seismologists near the Earth’s core. All aspects of the form and functions of the planet are interconnected, and intertwined with the rest of the Solar system. Any attempt to explain, for example, why are tectonic plates like a mosaic to cover the earth’s surface, it is necessary to consider the fact that none of the other planets in the Solar system such plates no. To understand the Earth, scientists have to figure out how it became unique in the Solar system. And for this you need to understand the mysteries of the first tens of millions of years.
“You can perceive it as a problem of the initial state,” — said studying the geysers and volcanoes Geophysics from the University of California, Berkeley’s Michael Manga. “The land we know today, emerged. And there are many uncertainties in the issue of where”.
Part of the puzzle
Once, among the endless succession held in Santa Barbara days, a week before his departure to Iceland, Jackson at the head of a group of scientists held a 2 mile walk along the beach to explore the mound of viscous oil — the place where sticky black material emerges from the rock, forming a soft, lush growths that you can push with your finger. Pressing the viscous substance and throwing rocks at it, scientists were thinking about the underground origin of the material and the approximate limits of its viscosity. When yours truly picked up a small piece to understand how it is easy, two or three people nodded approvingly.
The group is composed of geophysicists, geologists, mineralogists, geochemists, and seismologists arrived in Santa Barbara to participate in the annual conference of the joint Institute for dynamic Earth research (CIDER) at the Institute of theoretical physics Kavli. Every summer, the changing composition of representatives of these regions is found to last some weeks of the conference to share the latest research findings and to enrich mutually of ideas, because their common goal is the understanding of such a complex system as the Earth.
The complexity of Land, its distinctive features and, above all, the mysterious conditions of its emergence imply that, despite compiling a map of the Universe cosmologists and astronomers scanning the galaxy in search of a second Earth, progress in the understanding of our planet were always surprisingly slow. As we pushed our way from one mound of viscous oil to another, Jackson said exposed layers of sedimentary rocks on the cliff — some of them were horizontal, others curved and placed at an angle. Surprisingly, he said, but scientists are only in the 1960-ies agreed that the inclined sedimentary layers lose their stability and not accumulate under the corner. Only after this consensus was reached with respect to the mechanism explanation of the stability and strength of the Earth’s surface in General — the theory of plate tectonics.
A geophysicist from the University College London, Carolina Lithgow-Bertelloni studying tectonic plates, says that the German meteorologist Alfred Wegener is credited with entering the concept of continental drift (1912) in an attempt to explain why the earth’s land area arrays resemble the scattered pieces of a puzzle. “But the mechanism he could not explain — or rather I could, but it was complete madness,” said she.
A few years later, Caroline continued, the British geologist Arthur Holmes gave convincing evidence that from the point of view of Geology the solid and the solid mantle of the Earth moves smoothly, driven by emerging from the earth’s core heat; and the movement of the mantle, in turn, causes the movement of the surface. Even more evidence appeared during the Second World War. The magnetic properties of the seabed, mapped to conceal submarines, suggested that new crust is formed at mid-ocean ridge — underwater mountain range, lining the bottom of the oceans like the seam and extends in both directions to the edges of the continents. There, in the so-called “subduction zones”, ocean plates slide under the continental, causing earthquakes and bringing the water down where it proplase pockets in the mantle. As a consequence, melting occurs when magma rises to the surface obscure jerks, causing the eruption of volcanoes. (Volcanoes also exist far away from plate boundaries, for example, in the Hawaiian Islands and in Iceland. Currently, scientists explain this by the presence of plumes, and researchers like Walker and Jackson put them to the test and applied to the card using isotopic analysis.)
According to Lithgow-Bertelloni, physical description of the plates was finally made in the late 1960-ies, when the British geophysicist Dan McKenzie and American Jason Morgan separately proposed a quantitative basis for modelling of plate tectonics on a sphere.
In addition to the existence of the plates, almost all other information about them remains controversial. Than, for example, due to their transverse displacement? Where the end abdulrhaman plate — whether it’s those “clots”?— and how do they affect the dynamics of Earth’s interior? Why the crust is split into plates, and with other planets of the Solar system this did not happen? Another quite puzzling thing is the dual structure of oceanic and continental plates and how they were oceans and continents — all the necessary conditions for the existence of intelligent life. A greater amount of knowledge about how the Earth was formed, could help us understand how widespread in the Universe for Earth-like planets, and how likely is the occurrence in them of life.
Lithgow-Bertelloni says that the continents probably formed during that early process when gravity has streamlined the contents of the Earth concentric layers of iron and other metals sank to the center, forming the core and the rocky silicates remained in the mantle. However, low-density materials rose upwards, forming on the surface of the mantle, the crust is like the skin on the soup. Perhaps in some places it accumulated in the shape of the continents, and appeared in other oceans.
To find out what exactly happened and in what order, “much harder,” said Lithgow-Bertelloni because these stages precede the development of stratigraphic records and are “part of the melting process that took place in the very early stages of existence of the Earth.”
Until recently, scientists didn’t know about any geochemical traces of that era did not anticipate that it will be able to shed light on the most wonderful characteristics of the Earth. But a slight anomaly in the concentrations of tungsten and other isotopes currently form the first ideas about the emergence and transformation of the planet. These chemical indicators give hope for the emergence of information on the timing of development and the scheme of the Land surface of the early period, revealing how, why and when did its distinctive character.
Schematic chronicle
In their understanding of early Land his first giant leap mankind made when the astronauts of “Apollo” brought rocks from the moon, our less structural companion, whose origin was at the time a complete mystery.
Stones “looked gray and very similar to earth,” says Fouad Tera, which analyzed lunar samples at the California Institute of technology between 1969 and 1976. According to him, their lunar origin created a “sense of euphoria” all who had to keep them in hand. Some interesting features eventually appeared: “under the microscope we saw small glass spherical body — a bright, beautiful green, yellow, orange, and other,” recalls the now vosmidesyatitonnye Tera. These balls probably formed due to volcanic eruptions on the moon, when she was still young. But for the most part, he said, the Moon is the most ordinary things, nothing special.
Now, after time, it’s a surprise no longer: chemical analysis made at Caltech and other laboratories have shown that the Moon formed from the surface material of the Earth, which, apparently, was thrown into orbit as a result of the collision the proto-Earth at the age from 60 to 100 million years with other protoplanets in the crowded inner part of the Solar system. Although the details of the hypothesis “giant impact” (impact formation of the moon) is still hotly debated, it has become one of the key steps in the history of the Earth, moon and Sun that helped the rest to form a coherent picture.
Chemical analysis of meteorites helps scientists to identify earlier stages of the history of the development of the Solar system, including the moment that started it all.
First, 4.57 billion years ago, a nearby star became a supernova, spewing into space matter and forming a shock wave. Matter includes radioactive elements which immediately began to collapse, starting the clock mechanism, which studies the properties of isotopes, chemists are now measured with great precision. The shock wave swept through our cosmic neighborhood, gathering like a broom in a bunch there existed a cloud of gas and dust; and the increase in density triggered the gravitational collapse of clouds and the formation of brand new star — our Sun, surrounded by the “placenta” from hot debris.
Over the next tens of millions of years of debris surrounding the Sun field, accumulating, formed a larger and larger space gems, then coalesced into particles called “planetesimals”, and those, in turn, merged into a protoplanet that became mercury, Venus, Earth and Mars, the four rocky planets of the current of the inner part of the Solar system. And from the gas and ice in cold areas formed the giant planets.
Drifting in a crowded inner Solar system, the Earth in its infancy was experiencing frequent clashes with red-hot heavenly bodies that, as was long assumed, melted the planet to a state of a giant “magma ocean.” At the time gravity is turned sirenne the maintenance of Land in separate layers — core, mantle and crust. It is believed that each of the global melt destroyed the existing species, mixing their contents and erasing all geochemical differences from the original constituent elements of the Earth.
© flickr.com, ArchiveМиссия Project Apollo “Apollo-17”
The last that the Earth is a “giant clash” was likely then due to which the Moon formed; and minus the mass of the moon itself hitting the body has become the last significant addition to the mass of the Earth. Perhaps this point on the timeline — after at least 60 millions years after the birth of the Solar system, counting backwards from today, no more than 4.51 billion years ago — coincided with the beginning of a geochemical chronicle the past of our planet. “The notion that it destroyed much of the Earth is a giant clash of triggering geochronology — the idea is at least good,” says geochemist at the Carnegie institution of Washington-Rick Carlson. In those first 60 million years, “Earth may already be here, but we don’t have any evidence, because they were simply erased”.
Another discovery in the study of moon rocks dated to 1974. Tera with her colleague Dimitri Papanastasiou and their chief Jerry Wasserburg, who died in June and was a prominent figure in the field of isotope cosmochemistry, summarized isotopic analyses of samples from the same plot, but different missions for the Apollo program, identifying an appropriate time, a straight line called isochrone method. “When we are together with the rest applied to graph our data, I noticed a trend showing that about 3.9 billion years ago, something massive has left a mark on all the rocks on the moon,” said Tera.
Wasserburg dubbed this event the “lunar cataclysm”. Now it is more often called “late heavy bombardment”, which was a struck the moon 3.9 billion years ago — that is, after 600 million years after its formation — the flow of asteroids and comets that rocks on its surface and change its chemical composition. This meteorite bombardment probably touched the Earth and, given its size and gravitational pull. Having made such a momentous discovery in the history of the Solar system, Wasserburg “celebrated it in some bar in Pasadena”, taking with him his younger, more moderate colleagues, said Tera.
In 1974 the Earth was not found nor one stone of the time of the late heavy bombardment. It turns out that the formation of the oldest rocks of the Earth had been completed about 3.8 billion years ago. “This figure is striking,” says bill Bottke, an astrophysicist at the southwest research Institute in boulder, Colorado. It is, according to Bottke, suggests that the late heavy bombardment might have melted that the planetary crust that existed 3.9 billion years ago, once again destroying the entire geological history, and the new bark is hardened only after 100 million years.
In 2005 a group of researchers from the French of nice proposed a mechanism explaining the late heavy bombardment and some other mysteries of the Solar system, including the curious position of Jupiter, Saturn, Uranus and Neptune, as well as the sparseness of the asteroid belt and Kuiper. In their model, they argued that some time after the formation of gas and ice giant planets experienced a sudden destabilization of the orbits, so that they were forced to move. Simulation of Bottke and his colleagues indicates that migration of planets could cause a scatter of asteroids and comets, and, as a consequence, something very similar to the late heavy bombardment. It is likely that the comet, which, during this shake-up pushed out of the Kuiper belt inward, delivered to the surface water, which explains the presence of the oceans.
Due to the similarity of the ideas of the late heavy bombardment was widely recognized as an important step in the history of the early Solar system. But this news was unpleasant for the study of the Earth, as it meant that the reading of the geochemical history of the planet is not from the start — 4.57 billion years ago — or even since the formation of the moon 4.51 billion years ago, and is dated 3.8 billions years, and that all the clues of earlier events were lost forever.
Extending the stratigraphic record
The theory of the late heavy bombardment, and many other long-standing assumptions about the early history of the Earth and the Solar system have only recently become a subject of discussion, shedding light on the issues related to the so-called “dark ages of the Earth.” According to Carlson, “the evidence of this event that occurred 3.9 billion years ago, over time, become less clear”. For example, in the study of meteorites for signs of shock waves, “reveals many traces of collision by age 4.2, 4.4 billion years,” he said. “This event is the age of 3.9 billion years hardly stands out within the framework of the geochemical history of the planet.” He and other skeptics of the theory of the late heavy bombardment claim that delivered the “Apollo” samples could be selected biased. All expeditions were sent to the near to the Earth side of the moon, many of them were in the immediate vicinity of the basin of the Sea of rains (the largest visible from Earth the shaded area of the moon), which was formed as a result of a collision with another celestial body 3.9 billion years ago. Maybe this event influenced the collected “Apollo” samples of rocks and promote melting, large areas of the surface of the moon. This allows to make an assumption about a certain never took place cataclysm.
Secrets of the Earth formation
Moreover, the most famous oldest part of earth’s crust not 3.8 billion years as previously thought. In two regions of Canada were found fossils of the age of 4 and even of 4.28 billion years, refuting the idea that the late heavy bombardment completely melted the mantle and the crust of the earth 3.9 billion years ago. Some earlier part of the crust was not injured.
In 2008, Carlson and his colleagues proved the existence of fossils by the age of 4.28 billion years old in the Greenstone belt mountain system Nuvvuagittuq in Canada. After hearing about these findings, a geochemist from the University of Bristol Tim Elliott was surprised to find out that Carlson used the same method of determining the age of rocks, which previously used the French researchers, is based on a system of short-lived radioactive isotope called samarium-neodymiun method. Elliott decided to find in ancient rocks traces of even more short-lived system hafnium-tungsten, which would point to an even earlier time in Earth’s history.
The method of determining the age of rocks works as follows: every 9 million years (half-life) parent isotope hafnium-182 has a fifty percent chance to turn into a “daughter” isotope tungsten-182. The division of the parent isotope in two leads to its almost complete disappearance, and thus almost all of the hafnium-182 would be transformed into tungsten-182 after 50 million years after the appearance of the Sun in the supernova explosion.
That is why the ratio of isotopes of tungsten is represented by Matt Jackson of samples of olivine can be very significant: any change in a subsidiary concentration of the isotope tungsten-182 relative to tungsten-184 should reflect the processes that influenced the parent isotope hafnium-182 when he was still present in large quantities — the processes occurring during the first 50 million years of the Solar system. Elliott knew that this kind of geochemical information was considered destroyed by the processes of melting and the subsequent billions of years of mantle convection. What if wasn’t?
Elliott got in touch with Steven Arbatom, Professor Emeritus of Geology at Oxford University and, as he believed, “one of the greatest scientists in the study of ancient rocks”. “Arbat was full of enthusiasm, and I immediately went to him.” The scientist held Elliott in the basement of the building of the faculty of Earth Sciences, University of Oxford, where, as in many similar areas, a huge collection of rock specimens was located adjacent to the boiler house and warehouse of chairs. Arbat dug up specimens of the ancient breed age of 3.8 billion years, discovered them in the 1970-ies in the formation of Isua in Greenland.
Tim Elliott and his student Mathias Willbold crushed and processed rock samples from the isua formation and resorted to time-consuming chemical method of extracting tungsten. Then using cutting-edge mass spectrometer they measured the ratio of isotopes of tungsten. In one issue of the journal Nature in 2011 Elliott, Willbold and died in October Arbat reported that in the rocks of the isua formation age of 3.8 billion years contains 15 ppm more tungsten-182 than the world average, which is the first discovered “positive” tungsten anomalies on Earth.
The journal also reported about Richard Walker of Maryland and his colleagues, who a few months later announced another positive anomalies of tungsten, discovered in comatiites age of 2.8 billion years old, found in the Russian city of Kostomuksha.
Although rocks of Isua and Kostomuksha was formed long after the disappearance of hafnium-182, they, apparently, comes from materials with the earlier chemical telltale signs. Walker and his colleagues argue that the samples from Kostomuksha was most likely excavated from ancient hafnium-rich deposits in the Earth that have not been homogenized in the process of melting of the mantle. Walker and his co-authors wrote that the preservation of these deposits, which belong to the first 50 million years, and somehow had to be preserved even under the influence of lunar formation, “suggests that the components of the gown most likely was never shuffle”. This indicates the possibility of finding many other specimens of the early era.
Scientists believe that will be able to use tungsten isotope anomaly and other signatures of the surface layer as indicators of the composition of ancient Earth’s interior and, based on evidence from the past, create a map of the proto-Earth and discover the peculiarities of its formation. “You can see and trace the sequence of events that took place during the generation and modification of planets,” said Carlson. “You definitely have the opportunity to study in detail the first tens of millions of years of Earth’s history”.
Anomalies continued to be detected in the rocks of different age and origin. In may, a geochemist from the University of Quebec at Montreal Khanika Rizo, together with Walker, Jackson and their colleagues published a report in the journal Science, which reported the first positive tungsten anomalies in the modern rock age of 62 million years found in Baffin Bay, Greenland. Rizo put forward the hypothesis that these rocks were the result of a mantle plume that escaped from one of the “clusters” deep in the bowels of the Earth near its core. If these clots do rich tungsten-182, they are not tectonic burial, as suggested by many of Geophysics and relate to the period of “infancy” of the planet. Rizo suggests that it is the debris of planetesimals, which somehow survived in the process of formation of the Earth. She believes that the more collisions, the more possibilities exist for creating such a heterogeneous mantle. In this case, the depths of the early Earth have nothing to do with the images in the textbooks primordial magma.
On the surface began to emerge more and more evidence of the heterogeneity of the Earth’s interior. At the meeting in the beginning of the month meeting of the American geophysical Union, a group of scientists under the direction of Walker made a report, which reported a negative tungsten anomalies — about the shortage of tungsten-182 in relation to tungsten-184 is in basaltic rocks of the Hawaiian Islands and Samoa. This and other concentration of isotopes in the rocks talking about what led to their formation inferred plumes could occur from the primary deposits of metals, including tungsten-184. There is a possibility that these metals were not tightened in the nucleus in the process of modifying the planet.
Meanwhile, Elliott explains the positive anomaly of tungsten in ancient rocks of the earth’s crust, such as, for example, samples of the isua formation age of 3.8 billion years, the hypothesis that these rocks are hardened on the surface of the planet before them mixed up half a percent of the mass of the Earth, trapped on the planet thanks to a series of minor collisions.
However, there is evidence that this hypothesis is complicated, the concentration of gold and platinum in rocks of the isua formation in line with the average for the world, indicating that some part of the late the surface layer of sediments with them is still mixed. Still there is no integrated system that takes into account all currently available data. But, says Carlson, is “the period of discoveries” and not grandiose conclusions. Because geochemists consistently applied to map the plumes and primary field from the core to the crust, all the hypotheses will be tested, gradually shaping the history of the Earth.
Elliott continues to work to test his hypothesis about the later the surface layer of sediments. Temporarily replacing your mass spectrometer with a sledgehammer, he had picked up in Australia a number of samples of the earth’s crust aged from 3 to 3.75 billion years. Tracking the ratio of isotopes of tungsten from ancient times to the present day, he hopes to pinpoint the moment when the earth’s crust formed the mantle is fully mixed with the late surface layer of sediments.
“Such questions are not so easy to be solved,” said Elliott. “But you can always begin with simple ideas and trace their development.”
Natalie Wolchover writes for a dedicated science magazine Quanta Magazine. Previously, her articles have appeared in Popular Science, Live Science and other publications. He graduated from tufts University with a bachelor’s degree in physics, studied physics in graduate of the University of California at Berkeley, is the author of several scientific papers in the field of nonlinear optics. In 2015, her work was recognized the best articles in mathematics. In 2016, received the award for excellence in statistical reporting award for young science journalists behalf of the Evert Clark/Seth Paine.
