1 Billion Years of Earth's History are Missing
Almost 1.2 Billion years of Earth's history is missing. What happened and how? Let's find out:
To put it into perspective, Earth is almost 4.5 billion years old, and a billion years is almost a quarter of Earth's history gone! A billion-year gap in the fossil record! Geologists call this "The Great Unconformity".
Let's get some fundamentals cleared first:
If you go out today and start digging, the deeper you dig, the older the rocks you will find. Human and natural remains sink deeper down the Earth's surface due to a process called "deposition".
Then in another natural process called "cementation", these remains bind together until sedimentary rocks are formed a few million years later. This process goes on and on and thus the layers are formed, and the bottom-most layers turn into rocks.
All this while animals are dying. Their bones get covered in dust, succumb to sedimentation, and get encased by rocks, water penetrates this case, dissolves the bones, and eventually, minerals fill that void, forming a fossil.
Most of our understanding of our history has come through studying these layers of rocks that contain fossils and other remains.
These layers of rocks are called "strata", and each of them dates back to a certain period in the history of our planet, giving us a clear picture of that era. Stratigraphy (the study of strata) says that the lower the layer, the older the time it dates.
But history is not so predictable. While in one location new sedimentary rocks are being formed, in another location it might just stop due to geographical conditions. Wind and water causing erosion can just delete an entire layer of sedimentation.
This gap, called a "hiatus", can sometimes be millions of years old. These hiatuses create a noticeable difference in the angle, color, and texture of the rock layers. This feature is called an "unconformity".
James Hutton, a geologist, discovered an unconformity near Siccar Point in Scotland in 1787. He coined this "Hutton's Unconformity". This unconformity had a gap of 80 million years! Hutton made some theories about tectonic plate movements post this discovery. But this is nothing.
In 1869, whilst exploring the Grand Canyon, John Powell - an American geologist observed a bigger anomaly. He found an unconformity that proved a hiatus of about 1.2 billion years! It spanned across the entire North America!
After Powell's discovery, other formations around the world have been found that are missing the same time period of history. Collectively, these are called "The Great Unconformity." But what happened?
Well, we don't precisely know, but some have theorized what might have happened. It is called the "Snowball Earth" theory as it dates back 650 million years ago when the Earth's surface was thought to be covered with ice and glaciers.
Glaciers are large sheets of ice and are known to cause massive swathes of erosion. It is estimated that during this period (Cryogenian period), glaciers collectively caused the removal of 2-3 miles of the surface. But there is a climax.
Remember the topmost layer of rocks of the Great Unconformity, those layers are from a period called the Cambrian period. What's interesting is that during this period, the fossils suggest, the first ever bigger organisms (like fish) sprang into existence.
But how does it relate to the Snowball Theory? Well, these large glaciers carved the rocks and hit the oceans, depositing large amounts of minerals into the water that acted as a catalyst for life formation. It looks like we lost the 1 billion year of history to our oceans.
But, the Snowball Earth Theory is still a theory proposed in 1998. I think there is still a whole lot of research to be conducted to prove this theory and time will tell what happened to its ancestral period.