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It seems that the “boring billion” – a period in Earth’s history between 1,850 million and 850 million years ago – wasn’t so boring after all.
Geologists have found that our planet’s crust is “hot and thin” throughout the period, measuring only 25 miles (40 km) or less.
Today, under large mountain ranges, such as the Alps or the Sierra Nevada, the base of the earth’s crust can be as deep as 60 miles (100 km).
In addition, the relatively thin crust swirled around and was populated by a few low mountain ranges, created by milder tectonic activity.
The Boring Billion has always been considered the most boring time in Earth’s history, as little has happened to its climate, tectonic activity, or biological evolution.
The crushing of tectonic plates caused most of the Earth’s mountains to form – a process called “orogeny” – including the Himalayas (pictured). But during the Boring Billion, Earth populated by lower mountain ranges, created by milder tectonic activity
The new study, led by Christopher J. Spencer, a geologist at Queen’s University in Kingston, Canada, challenges that idea.
“During the Boring Billion in particular, oxygen levels were low and there is no evidence of glaciation,” the team says in its article, published in Geophysical research letters.
“We propose that the thin crust at this time is a product of high temperatures resulting in greater crustal flow and therefore lower mountain ranges.”
The Earth’s lithosphere – its outermost rocky shell – is made up of about 15 tectonic plates, each of different shapes and sizes.
Strong seismic activity can be detected along the boundaries of the tectonic plate, where the plates rub against each other.
When this happens, plate tectonics cause natural disasters around the world, including earthquakes, tsunamis, and volcanic eruptions.
But the crushing of the tectonic plates caused most of the Earth’s mountains to form – a process called “orogeny” – including the Himalayas.
The map shows the tectonic plates of the lithosphere on Earth. Orogeny is the process by which tectonic plates converge and mountain systems are created
“In the case of the Andes and the Himalayas, the orogeny has led to a significant thickening of the continental crust”, explain the authors of the study.
“Recent attempts to provide geochemical approximations of crustal thickness have enabled geologists to track crustal thickness through geologic time. “
Previous knowledge that the earth’s crust was thin during the Boring Billion has led some to believe it was a period of “orogenic quiescence” or dormancy.
But the authors of this new article say that the geological record is “plentiful” with ancient orogenic belts during this period, as evidenced by metamorphic and igneous rocks.
“In particular, metamorphic rocks display higher than normal temperature / pressure ratios, indicating an unusually warm crust,” they say.
The Earth has three layers: the crust (made of solid rocks and minerals), the mantle, and the core. Today, under large mountain ranges, such as the Alps or Sierra Nevada, the base of the earth’s crust can reach a depth of 100 km.
This created a style of plate tectonics much like “a waltz on a slippery dance floor”, the Guardian reports – rather than the violent dodgem-car style we see today.
Learning more about the Boring Billion – which occurred in the middle of the Proterozoic Era – could shed light on how contemporary tectonic plates have become so powerful.
During the Boring Billion, the most advanced life on Earth was algae, and oxygen levels were much lower than they are today.
But despite its boring reputation, a study in 2017 discovered that the origin of photosynthesis in plants dates back to 1.25 billion years ago during the period.
The era may have paved the way for the proliferation of more complex life forms that peaked 541 million years ago with the so-called Cambrian Explosion.
The Cambrian explosion saw an explosion of new animal phyla, likely due to a surge in oxygen, including arthropods with legs.
