It seems 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 was ‘hot and thin’ throughout the time period, measuring just 25 miles (40km) or less.
Today, the base of the Earth’s crust can reach as deep at 60 miles (100km) in large mountain ranges such as the Sierra Nevada and the Alps.
Furthermore, the crust was thin and was populated with low mountain ranges that were created by less gentle tectonic activity.
The Boring Billion was always considered the most dull period in Earth’s past, due to the fact that not much happened to its climate or tectonic activity.
The formation of most of Earth’s mountains has been caused by tectonic plates colliding together – a process known as ‘orogenesis’, which includes the Himalayas (pictured). Earth was populated with lower mountain ranges created by gentler tectonic activity during the Boring Billillion.
The new study, led by Christopher J. Spencer, a geological scientist at Queen’s University in Kingston, Canada, challenges this idea.
‘Notably during the Boring Billion, oxygen levels were low and there is no evidence of glaciation,’ the team say in their paper, published in Geophysical Research Letters.
“We propose that the thin crust observed at this time is due to high temperatures, which result in greater crustal flow, and thus lower mountain ranges.
Earth’s lithosphere – its rocky, outermost shell – is formed of around 15 tectonic plates, each of different shapes and sizes.
You can detect powerful seismic activity along the tectonic plates’ borders, where the plates rub up against one another.
This is when plate tectonics can cause natural disasters all over the globe, including earthquakes and tsunamis.
But tectonic plates smashing together has caused the formation of most of Earth’s mountains – a process called ‘orogenesis’ – including the Himalayas.
Map showing the tectonic plates in the lithosphere of Earth. Orogenesis refers to the process by which tectonic plates collide and mountain systems are formed.
The study authors explain that orogenesis caused significant thickening in the continental crust in the case of the Himalayas and the Andes.
“Recent efforts to provide geochemical proxy for crustal thickness has allowed geologists track the thickness through geologic times.”
Previous knowledge that the Earth’s crust was thin during the Boring Billion has led some to believe that it was a period of ‘orogenic quiescence’ or dormancy.
The authors of this paper claim that the geologic record is “rife” with ancient orogenic belts at this time, as evidenced in metamorphic andigneous rock.
They state that metamorphic rocks, in particular, have higher than normal pressure and temperature ratios, which indicates unusually hot crust.
The Earth’s three layers are the crust (made from solid rocks and minerals), mantle, and core. The Earth’s crust can reach as deep today as 60 miles (100km), depending on how high the mountain ranges are, such as the Sierra Nevada and the Alps.
This created a style of plate tectonics much like ‘a waltz on a slippery dancefloor’, the Guardian reports – rather than the violent dodgem-car style we see today.
Understanding more about the Boring Billion – which occurred in the the mid-Proterozoic era – may shed more light on how contemporary tectonic plates became so powerful.
The Boring Billion was when algae was the most advanced form of life on Earth. However, oxygen levels were much lower than they are now.
But despite its boring reputation, a study in 2017 found that the origin of photosynthesis in plants dated to 1.25 billion years ago during the period.
This era may have been the catalyst for the development of more complex life forms, which culminated in the Cambrian Explosion 541 million years ago.
The Cambrian Explosion saw an explosion of new animal phyla. This may have been due to a steep increase in oxygen, which included arthropods with legs.