There's a Giant Hole In Earth's History

Hello, Thoughty2 here. If you've ever found yourself turning over furniture while frantically searching for your car keys, you know how easy it is to lose something. Maybe you've lost your phone, your wallet, or your will to live. But of all of them, the biggest mystery is how we lost a billion years of

history

. This is much more serious than when you found the keys in the bread basket, because there is a colossal blank space in our planet's past and no one is quite sure where we keep it. To put things into perspective, a billion years is almost a quarter of the Earth's existence.

And yet, there is a billion-year gap in the fossil record that geologists call "The Great Unconformity." Let's dig a little deeper, shall we? Speaking of which, if you ran outside right now and started digging, you would discover older layers of rock as you went deeper. First, you'd find an Alanis Morisette tape from the '90s, maybe a disco ball from the '70s, but eventually you'd dig up some Roman coins and other assorted artifacts. So why do both human and natural remains sink deeper into the

earth

as time passes? Well, the Earth's surface is constantly covered in fine particles like sand and dust;

This sediment accumulates in an agonizingly slow process called deposition. Then, in another process called cementation, these mineral particles gradually join together until, a few million years later, sedimentary rock is formed. Then another layer of rock forms on top, then another, and another, and so on, until the ground beneath your feet is like a bagatelle, a bagatelle of rock, with millions of layers formed over millions of years, and not even one. one of them contains custard, what a tragedy. But during all this sedimentation and cementation the animals are doing their usual party trick: dying. All the soft, slippery bits are eaten or decomposed, but sometimes the harder parts, such as bones, shells and husks, become covered in dust, slowly succumbing to sedimentation and becoming encased in the rock.

Over time, water penetrates this rocky tomb, which dissolves the biological remains it contains. Over time, the minerals fill the void and form a fossil, which of course is nothing more than a rock replica of the creature that once resided there. Most importantly, however, this fossil is frozen in time, enshrined in the sedimentary rock of the time in which the animal lived. Much of our understanding of the

history

of the planet and of life itself comes from studying the sequence of sedimentary rock layers and the treasures they have trapped over time. Often the different layers, called strata, are clear and distinct, each revealing something unique about the time in which it formed.

The wonderfully fun hobby of studying strata is called stratigraphy, and one of its guiding principles is the law of superposition. which states that “if left undisturbed, the lower the rock layer, the older the rock.” It's not exactly rocket science, but it does mean that, in general, when you look at a cross section of geological formations, you have a pretty clear picture of the passage of time. But unfortunately the story is not so predictable. While in one place new layers of sedimentary rock form, in another the conditions may change and sedimentation stops. Wind or water erosion can move particles to other locations, effectively eliminating part of the geological record.

After a time, sedimentation may resume, but these temporary interruptions will forever leave a gap in the rock record, and sometimes that gap, called a hiatus, can last for millions of years. It's like pausing, rewinding, and then re-recording during a very long conversation: the final recording will be missing parts that are unrecoverable, and if these parts are integral to the meaning of the conversation, then everything will no longer work. make sense. When these pauses occur, it creates a noticeable difference in the angle, color, and texture of the new rock on top, as you can see here and here.

Geologists call this characteristic unconformity. It was the Dane Niels Steensen, considered the father of stratigraphy, who first outlined an unconformity in 1669. But it was a Scottish farmer named James Hutton who discovered the first significant unconformity. While walking near Siccar Point in Scotland in 1787, he noticed the striking difference between the lower and upper rock formations and coined a name for it: "Hutton's Unconformity." If this seems a little rude to you, but you're not sure why, join the club. The lower layer of grayish rock is mainly made up of deep-sea deposits from about 425 million years ago. But the reddish top layer was deposited by rivers and streams about 345 million years ago.

This is a pause of about 80 million years. It was thanks to this discovery that Hutton helped develop some important theories about the movement of tectonic plates and the forces that shape the face of the Earth. Some geologists call Siccar Point a geological sanctuary, which shows how incredibly strange both this formation and geologists are. However, the most surprising discrepancy was found in 1869, when John Wesley Powell was observing a strange mound. As he traversed the Grand Canyon, he noticed vertical rock formations crashing into horizontal formations. Channeling the supreme creativity of his geological predecessors, he called it “Powell's nonconformity.” But it has since become more commonly known as Powell's Great Unconformity, and there are two surprising reasons why it deserves the title "Great Unconformity." First, the unconformity actually spans an entire continent, stretching across Laurentia, which is the name of the ancient heartland of North America.

Second, many other unconformities had been un

earth

ed around the world by now, but they mostly represented small gaps, at least on a planetary scale, perhaps tens of millions of years old. But the smallest time interval between the two rock layers in the Great Unconformity is a modest 250 million years, and the largest is more than 1.2 billion years. That's right, that missing slice of the prehistoric pie sandwiched between these two unassuming rock formations represents up to 1.2 billion years of lost history, and we have no idea where it went. But there is much more to this rocky oddity. Since Powell's great discovery, a few more formations have been found around the world that have had the same time period removed from their record.

Together we collectively refer to this as "the Great Disagreement"; It is a mystery that spans the entire planet and more than a billion years of lost knowledge. Take the example of the Grand Canyon, here the 525 million year old Cambrian era Tapeats sandstone sits comfortably on top of the 1.7 billion year old Vishnu basement rocks, which date back to the Precambrian era; like I said, an epoch interval of 1.2 billion years: strange, right? Head to Missouri's Ozark Plateau, where we'll see a similar sight: 500-million-year-old sandstone sits suspiciously atop 1.4-billion-year-old granite, representing a 900-million-year interval. For the sake of all things igneous, what the metamorphic heck is going on here?

Well, some have suggested a theory to explain the Great Discord. And it's called the "snowball Earth" theory: it refers to a time during the cryogenic period, about 650 million years ago, when the Earth's surface was thought to be covered by glaciers and ice sheets. Glaciers are capable of causing erosion on a massive scale as they advance across landscapes, and it is estimated that together they moved two to three miles away from the earth's surface; basically, the surface of the earth was exfoliated. Remember how I said that the youngest rocks sitting on top of the Great Unconformity around the world date back to a period called the "Cambrian Period"?

Well, what's really interesting here is that the Cambrian period was when the largest explosion of life in the history of our planet took place. During a short timeline of just 11 million years, approximately 541 to 530 million years ago, the original ancestors of almost all life forms we know today emerged; for example, that was when fish first appeared. There was life before this event, but this brief window was when Mother Nature downed a Redbull, snorted some cocaine, and hit the big evolutionary boost button. So how does this relate to the "Snowball Earth" theory? Well, when all of these ice flows started hitting the ocean, they deposited gigantic amounts of nutrient-rich minerals into the water, where, the theory goes, it was responsible for the aforementioned explosion of life.

More than a billion years of sedimentary rock was removed from the face of the planet by glaciers and then submerged in the breeding ground of evolution, the ocean, where the numerous minerals contained within it acted as a catalyst for life such as We know her today. So in the end it seems like we lost a billion years of history on the back of the couch; only the sofa in question turns out to be the bottom of the ocean. But Snowball Earth is still a theory that Dr. Paul Hoffman only put forward in 1998. And if you ask me, two decades doesn't seem like enough time to definitively explain a billion years of lost history.

Maybe one day new techniques or technologies will shake up the world of geology and allow us to fill in more of the missing gaps in our planet's very long, empty history book, but until then the Great Unconformity will remain a great mystery. Thanks for watching.