How the Earth Lost Billions of Years of History (Geographically)

The earth is a strange place, with thousands of undiscovered creatures in the deep seas, beautiful constructions from long lost civilisations, and languages to cultures that will never emerge again. But by far ,the most impressive mystery is of how  a billion of the Earth's history has been completely erased from the Earth's surface.

Yes, you heard/ read that right! A billion of the Earth’s geographical history has been erased, and no one really knows why. To put things into perspective, a billion years is almost a quarter of the earth's entire history. This billion year gaping hole is called The Great Unconformity.

Let's dig a little deeper ,shall we?

If you were to dig into the earth's crust you'd be essentially going back in time. At first, let's say you find a Madonna tape from the 90s, then a disco ball, from the 70s but eventually you’d reach things like human remains from the 700th century BC !

Now why is it that human remains and objects tend to be deeper in the earth the  farther in time they lay there? This is due to the fact that the earth's surface is constantly being littered with fine particles (sand, dust…etc) in an agonizingly slow process called deposition. Then ,through another process called cementation ,these particles bind together until finally sedimentary rock is formed.

After that, another layer of rocks piles on top, then another, then another, until eventually the initial layer of rock is buried under thousands of pounds of other rocks. Like a multilayered cake of geological history!

But ,while this is happening, animals do what they do best. Die. So, all the soft and meaty bits are eaten up by bacteria, fungi or scavengers until only the hard bone remains. The bones are eventually left to be covered with fine particles, succumbing to sedimentation ,and, through time and the right conditions, become encased in their own makeshift rocky tomb.

As time goes on, water penetrates the rock reaching the animal remains. Which dissolves the biological remains (the bones) within. Minerals eventually fill this void ,and a fossil is formed. This is important because most of our understanding of the earth is based on studying the sequence of sedimentary rock  layers and the hidden history they've trapped through time.

Each layer, called  a strata, is distinct and unique with each revealing something interesting about the era they were formed. The study of stratas is called Stratigraphy, and one of its guiding laws is called The Law of Superposition , which states that “if undisturbed, the lower down the rock the older it is” .Not exactly rock-et science, but explains what has been stated up to now.

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Now, of course, the natural world isn't as predictable. So, due to things like water erosion the soil layers are disturbed and there will be “pauses” 'in the timeline of the layers of the earth, which are called a hiatus. Sometimes those gaps will be as large as millions of years long, and especially if it is an integral part of the earth's history, it will be a huge loss to the geologic record. When these hiatuses happen it makes a noticeable difference in the angle , texture and color of the new rock.

Geologists call this feature an Unconformity. It was first coined by a Danish man called Niels Steenson (the father of stratigraphy), who first drew one in 1669. But it was a Scottish farmer called James Hutton who documented the first significant unconformity (Hutton's Unconformity, at Siccar Point) with a hiatus of 80  million years. It was based on his discoveries that he could make major breakthroughs about erosion, the movement of tectonic plates, and the forces that shape the earth.

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Some geologists call Siccar point a geologic shrine, which is a testament to how strange geologists and the rock formation actually is.  

However, the strangest unconformity was discovered in 1869 by John Wesley Powell whilst traversing through the Grand Canyon, he found that a vertical rock formation was jutting up against horizontal formations ,and with the creativity bestowed upon from his geologic forefathers him he called it Powell’s Conformity, although it is now more commonly referred to as Powell's Great Conformity.

There are two reasons for calling it a Great Unconformity :

Firstly, the unconformity actually spans an entire continent, spanning across Laurentia (the ancient heart of North America), Secondly, other unconformities had also been reported , but they had been on a smaller scale in the grand scheme of our planetary history. They usually spanned from 14 million to 25  or 80 million like in Siccar Point. The smallest difference in Powells Unconformity , however, had a modest 250 million, while the greatest is over 1.2 billion years.

That missing piece from the great prehistoric pie spans a whopping 1.2 billion years of missing history- and we have no idea where it went.

The strangest part of this mystery is that there have been different unconformities discovered around the world during the same time period, millions of years plucked from the geologic record. Together ,we collectively refer to this as The Great Unconformity.

It's a mystery that spans the globe and hundreds of millions years to a billion years. Take The Grand Canyon as an example, the 525 million year old Cambrian Tapeat Sandstone sitting upon the 1.7 billion year old Vishnu Basement Rocks dating back to the precambrian era has a time difference of 1.2 billion years. If you go over to Missouri you'll see a similar sight in The Ozark Plateau,  a 500 million year old sandstone sits upon 1.4 billion year old granite.

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Weird, right? Now , you may be wondering “What in the metamorphic heck is going on here?”. Now, there are a few theories on why this may have happened. The most popular of which is The Snowball Earth theory. It refers to the time during the Cryogenian time period, around 650  million years ago, where the Earth was thought to be covered in ice. Hence the name, Snowball Earth Theory. 

During this time, the earth was covered in giant ice sheets and Glaciers. Glaciers are capable of eroding the Earth's surface on a massive scale, and it has been estimated that they have removed two to three miles of the Earth's surface. 

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The younger rocks that sit atop The Great Unconformity all conspicuously date back to the Cambrian period . Well ,what's really interesting here is that the Cambrian period  happened to be when the biggest explosion of life occurred on the planet in a (relatively speaking) small window of time: 11 million years. 

This occurred between 541 to 530 million years ago, and all of the original ancestors of all the life forms that we currently know today sprung into existence. There was life before this event, but this period was when mother nature downed an energy drink and went into overdrive, pushing the evolutionary fast button.

How does this all relate to The Snowball Earth theory? The idea is that when all these ice deposits deposited all the rock and soil into the ocean, it also deposited gargantuan amounts of minerals into the ocean. When the ice deposited such large amounts of nutrient rich soil in the oceans it was responsible for the aforementioned explosion of life.

So, in the end with a billion years of geographical history down the drain (although the metaphorical drain turns out to be the bottom of the ocean), The Snowball Earth   theory remains just that: a theory. One posed as early as 1998 by Dr.Paul Hoffman. 

Maybe one day we will discover new technologies, or techniques that will rock the Geology world and reveal the secret once and for all. But until then, The Great Unconformity will be a blank chapter in our planet's very long- and very empty- history book.