Friday, May 27, 2022
Photo: Getty Images, Grate Canyon
Photo: Getty Images

Traces of a billion years are missing from the rocks on Earth. How could they disappear from the face of the Earth? Scientists are closer to solving this mystery. The key here is the snowball-Earth hypothesis, i.e. glaciation that bound the entire planet to the equator.

Towards the end of the 17th century, Scottish explorer James Hutton noticed that the cliffs of Siccar Point on the east coast of Scotland were missing the rock traces that were to be expected. A similar lack was noticed by the American geologist John Wesley Powell in the Grand Canyon of Colorado during his 1869 expedition. Well, the oldest sedimentary rocks in the Scottish cliffs were 435 million years old, in the Colorado Canyon about 550 million. Below them is a layer of crystalline rock that is about 1.7 billion years old. Between them there is no trace of rock from a long period of nearly 1.2 billion years!

How can "rocks be missing"? For example, sedimentary rocks are often formed on an annual basis - the lighter layer of sediment comes from summer, and the darker layer from winter. By counting these darker and lighter layers (and dividing the number by two), you can estimate how old a rock is. There are also other indirect methods of age estimation.

Powell estimated that the thickness of the sedimentary rocks in the Grand Canyon should be almost 3,000 meters. Meanwhile, it is just over 150. What took - and where - the traces of over a billion years of history, more than two and a half thousand meters thick? This was something Powell couldn't explain. He called the break "The Great Disagreement."

The "Great Incompatibility", or where the billion-year-old rocks have gone

Today, geologists date rocks by examining the proportions of radioactive elements. Uranium turns into lead over time. The proportions of these two elements make it possible to determine how many years a rock can be - the older it is, the less uranium should remain in it and the more lead there should be. This is the oldest radiometric dating method first used in 1907. Today, the proportions of other elements are also used.

They also indicate that in many places around the world there is a gap in the geological history of the Earth over a billion years. Geologists call such gaps nonconformities. They are not uncommon. They are traces of the fact that the rocks were taken by water or shifting glaciers, or were moved by colliding continents and rising mountain ranges.

However, these are inconsistencies that have occurred in different places and at different times. The "Great Disagreement", on the other hand, is discovered in many different places around the world and always points to the same period in history. Something very dramatic must have happened all over the Earth that took traces of over a billion years of its history.

 

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Photo: Getty Images, Grate Canyon
Photo: Getty Images

Traces of a billion years are missing from the rocks on Earth. How could they disappear from the face of the Earth? Scientists are closer to solving this mystery. The key here is the snowball-Earth hypothesis, i.e. glaciation that bound the entire planet to the equator.

Towards the end of the 17th century, Scottish explorer James Hutton noticed that the cliffs of Siccar Point on the east coast of Scotland were missing the rock traces that were to be expected. A similar lack was noticed by the American geologist John Wesley Powell in the Grand Canyon of Colorado during his 1869 expedition. Well, the oldest sedimentary rocks in the Scottish cliffs were 435 million years old, in the Colorado Canyon about 550 million. Below them is a layer of crystalline rock that is about 1.7 billion years old. Between them there is no trace of rock from a long period of nearly 1.2 billion years!

How can "rocks be missing"? For example, sedimentary rocks are often formed on an annual basis - the lighter layer of sediment comes from summer, and the darker layer from winter. By counting these darker and lighter layers (and dividing the number by two), you can estimate how old a rock is. There are also other indirect methods of age estimation.

Powell estimated that the thickness of the sedimentary rocks in the Grand Canyon should be almost 3,000 meters. Meanwhile, it is just over 150. What took - and where - the traces of over a billion years of history, more than two and a half thousand meters thick? This was something Powell couldn't explain. He called the break "The Great Disagreement."

The "Great Incompatibility", or where the billion-year-old rocks have gone

Today, geologists date rocks by examining the proportions of radioactive elements. Uranium turns into lead over time. The proportions of these two elements make it possible to determine how many years a rock can be - the older it is, the less uranium should remain in it and the more lead there should be. This is the oldest radiometric dating method first used in 1907. Today, the proportions of other elements are also used.

They also indicate that in many places around the world there is a gap in the geological history of the Earth over a billion years. Geologists call such gaps nonconformities. They are not uncommon. They are traces of the fact that the rocks were taken by water or shifting glaciers, or were moved by colliding continents and rising mountain ranges.

However, these are inconsistencies that have occurred in different places and at different times. The "Great Disagreement", on the other hand, is discovered in many different places around the world and always points to the same period in history. Something very dramatic must have happened all over the Earth that took traces of over a billion years of its history.