Research has revealed what eradicated billions of years from the "memory" of the Earth.
When "the window has" the whole planet, it is a mystery that has been solved for almost two hundred years.
Before the world began, something dramatic happened on our planet. All over the world, much of Earth's memory has been erased – miles of rock records.
In a new study, geologists at the University of California at Berkeley have confirmed the guilt of one of the suspects. They have succeeded in researching two peculiarities – extreme variations in the number of ancient craters and in the isotopic composition of ancient zircons.
The great disagreement that geologists call the largest "window in the memory of the Earth" seems to have caused the devastating activity of the glaciers that have repeatedly covered the entire planet.
The research work was published by the journal PNAS.
Missing billions of miles3
Rock sequences are the memory of Earth. Their mineral or chemical form, structure, and composition indicate when, where and under what conditions they were created, and what they have gone through since then.
Geologists read them as the true crown of praise.
Due to the devastating effects of erosion and erosion (drainage), the rock record is incomplete. The biggest difference is observed in old age (2.5 to 0.5 billion years ago).
In some places there is no shortage of more than 1.5 billion years. In a way, it removed the continent from several billion cubic kilometers of rock.
A mystery of twelve years
Geologists noted a great deal of disagreement in the nineteenth century.
It is surprising that the layers deposited on the surface (eg in the rivers) by the sites are placed directly on the deep rocks, which are created due to the high temperatures and pressures in the depth of up to 10-15 km.
Of course, they have known many processes that destroy rocks in all regions. For example, you can do it with mountain bands.
But in case of major disagreement, the destruction occurred not only in some areas but virtually where the continent lay on the ocean.
"It is difficult to imagine a sufficiently drastic increase in horticultural activity, which would cause such erosion of intense erosion," the authors write in the research paper.
In addition, the search for a solution complained of the fact that the destruction that led to a major disorder in some places was much more destructive than elsewhere.
Photo gallery / 3
An example of geological disorder – the horizontal layers were formed much later than tilted in their subsoil, with erosion in that half time for millions of years.
Source: Patrick Mackie
The main suspect
Several discoveries have suggested that one of the possible explanations is the activity of glaciers. As demonstrated by the galloping rocks in northern Europe or northern Canada, in the recent Ice Age they acted as a true continental treadmill tractor.
The hope of this explanation encouraged the discovery that there were special glaciations before 717-660, 641-635, and before about 580 million. The first two apparently around the world.
"The emergence of major disagreement would require erosion by removing 0.0625 mm per year, which is almost one hundred times smaller than the recent measures for the Greenland iceberg," the authors wrote.
It has also been found that the erosive effect of glaciers ranges from 0.01 mm to 10 cm per year, depending on many factors, such as the velocity, thickness or temperature of the lower layers.
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The rocky bed in Norway, which exposed and smoothed the glaciers in the fourth quarter.
Source: Siim Sepp
Search for evidence
Old-fashioned joys are not just enough to create a big discrepancy, but they can also explain their varying intensity in some areas. And to make that explanation, geologists found that they turned their attention to the craters after the impact of the asteroids.
"Deep erosion in large areas would greatly reduce the number of craters, except for larger craters," the authors explain.
In analyzing the number of craters of different ages, they found that their quantity for each geological period roughly corresponds to the size of the area in which the rocks of the given period emerge.
This rule applies only to rocks less than 550 million years old.
Only two survived 700 million years ago. Both large and preserved only torzovite. They have evidence of removing about 5 or 10 miles of rocks.
They also found that the number of craters smaller than 10 km fell dramatically to zero on rocks more than 600 million years ago. "These findings agree with what we would expect from the gradual erosion of glaciers," geologists say.
Finally, the researchers analyzed the chemical composition of 30,000 zirconia formed by volcanic activity near the places where the oceanic shell grew in the bowels of the planet.
It is important to note that the amount of radioactive isotopes of hafnium-176 in such zirconia reflects the volume of sedimentation of continental origin covered by the cloudy ocean floor.
As expected, in the zircon of the ancient 700-600 million years, geologists found an extreme loss of hafnium-176.
Only the massive erosion of continents by the glaciers could have caused it. It is precisely in the case of large-scale glaciation that the ocean floor inflates an excessive amount of terrestrial material.
Thus, with the other evidence, they also confirmed the hypothesis that large-scale disagreements had created long lasting glaciations.