A shocking discovery has been made: there is a billion years lost and no one knows where it went.
This record is found in the rock strata of the earth's crust, and this gives clues to scientists of the earth's distant past. For one thing, it should be complete yet something is missing there.
The Great Unconformity was discovered by John Wesley Powell in 1869, in the layers of the Grand Canyon, where he found out that a billion years was missing in certain rock layers. Since then scientists have been trying to crack the secret.
In response to the missing time, many scientists have developed ideas and hypotheses why it is missing. UC Santa Barbara geologist Francis Macdonald and his colleagues may have the answers to these questions. This was pursued in a study that is in the National Academy of Sciences.
According to Macdonald, unconformities all through the rock record is evident, and they just gap the rock record that is unaccounted for. The Great Unconformity is a large or even a global gap that needs explaining.
One idea is that the glaciers carved and scoured away kilometer of rock strata about 720 to 635 million years ago (MYA) on frozen earth that was covered in ice. It is plausible because of the Cambrian explosion that saw life developing rapidly, due to nutrients in the frozen ocean.
Macdonald is not convinced of the hypothesis, similar to the theory of the earth as a giant snowball which is doubtful, even with the missing rock.
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He added that the Great Unconformity happened long ago in the past with the fact earth is unpredictable. These rocks are buried and eroded so much, there is no way to tell.
Testing the idea was done with Thermochronology, which is measuring the variation of heat as it changes from the core to surface of the earth. A difference of 50 degrees Celsius for each kilometer of depth, the changes are marked on the minerals.
Radioactive elements breakdown in rock and Helium-4 is made and generated. Tracking how much helium, thorium and uranium to gauge how old as paleo-thermometer, and how much movement is there.
As a result, scientists can use the ratio of helium to thorium and uranium in certain minerals as a paleo-thermometer. This phenomenon enabled Macdonald and his coauthors to track how rock moved in the crust as it was buried and eroded through the ages.
Macdonald said that it is happening through tectonics, and it can be studied now.
Samples were taken from granite below the boundary of the Great Unconformity at Pikes Peak in Colorado. Extracting grains of resilient mineral, zircon, from the stone and analyzed the radio nucleotides of helium contained inside. Revealing that several kilometers rock was eroded from 1,000 to 720 million years ago (MYA). If this is proof of snowball earth, then it might have explained it already.
The Great Unconformity is related to the Snowball Earth and the sudden burst of life in the Ediacaran and Cambrian, this is the billion years lost in the geologic record, and solving it will be a big deal.
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