Episode 164 – The “Boring Billion”

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Earth’s deep history is filled with dramatic cases of changing climates, shifting continents, and evolutionary leaps and bounds, but between roughly 1.8 and 0.8 billion years ago, things were seemingly stable. This episode, we explore the many mysteries of the so-called “Boring Billion.”

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Earth’s “Middle Age”

The early Proterozoic Eon, around 2.5 – 2.0 billion years ago, was a tumultuous time period, featuring a dramatic rise in oxygen levels, the formation of the supercontinent Nuna/Columbia, and the earliest stages in the evolution of eukaryotic life.

Similarly exciting was the late Proterozoic Eon, around 800 – 600 million years ago, which saw a series of global “Snowball Earth” ice ages and the appearance of the earliest animal-like complex life.

But in between is a time period most remarked upon for being unremarkable. This time, roughly 1.8 – 0.8 billion years ago, has been called the “Boring Billion,” the “Barren Billion,” and “the dullest time in Earth’s history,” due to an apparent stasis of tectonic, atmospheric, and biological evolution.

Geochemical evidence from this time period indicates a lack of major climate changes or shifts in oxygen levels in the atmosphere or ocean. The geologic record from this time is generally lacking in the sorts of rock formations associated with mountain-building, crust subduction, and other major side effects of plate tectonics. And the fossil record during these billion years doesn’t show evidence of major innovations in the evolution of life. This “Boring Billion” was seemingly a time when things on Earth slowed down and stabilized for a while, and this has intrigued and puzzled scientists for decades.

A timeline of major events in Earth history, highlighting the “Boring Billion.”
Image by J. Hirshfeld, CC BY-SA 4.0

Why So Boring?

It’s possible that the “Boring Billion” wasn’t quite as boring as it first seems. The geologic record of the Proterozoic Eon is sparse, which makes it difficult to make confident statements about global trends. And indeed, some recent studies have identified potential evidence for fluctuating oxygen levels, more diverse ancient life, and more complex tectonic activity than previous research has suggested.

Examples of fossils from the “Boring Billion”
Left: A 1.4 billion year old stromatolite (bacterial mat fossil) from Glacier National Park. Stromatolites were quite diverse during this time period. Image by James St. John, CC BY 2.0
Right: A 1.6 billion year old fossil of Ramathallus, identified as an ancient red algae, among the oldest known.
Image by Bengston et al 2014, CC BY 4.0

It’s possible that this “Boring Billion” was a time of transition for our planet. Some scientists have suggested that the apparent slowdown of tectonic activity is indicative of a more ancient style of plate tectonics, a less dramatic precursor to the familiar dynamics of crustal movement we see today. Other research has indicated, using fossils and DNA evidence, that several major evolutionary innovations might have happened during this time, including the origins of multicellularity and sexual reproduction, and that perhaps the unusual conditions of this time encouraged new adaptations that laid the foundation for the later evolution of complex plant and animal life. Because of this, the “Boring Billion” might be a crucial time period to study to understand the development of Earth as we know it.

Depiction of the supercontinent Nuna/Columbia, which included most of the Earth’s continental landmass for much of the “Boring Billion.” Image by Alexandre DeZotti, CC BY-SA 3.0

Eventually, this “middle age” came to an end as this seemingly-stable balance was interrupted. Tectonic activity became more dramatic, climate and atmospheric conditions shifted, and shortly thereafter life blossomed into complex new forms. There’s plenty of research left to be done to understand how the “Boring Billion” began, how it ended, how it impacted life as we know it, and just how “boring” it actually was.

Learn More

Myth-busting the Boring Billion
Earth’s ‘boring billion’ years of stagnant, stinking oceans might actually have been rather dynamic

Earth’s middle age, 2014 (technical, open access)
The Boring Billion, a slingshot for Complex Life on Earth, 2018 (technical, open access)
The Mesoproterozoic – no “boring billion” – 2019 (technical, open access)


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