Completely Incomplete
Earth’s Electromagnetic Field and the Human Perception of History
How does Earth’s magnetic field set a compass in motion? And how much does paleomagnetic data contribute to how we understand the history of our planet?
Earth’s electromagnetic field: It serves as the basis upon which our planet’s geologic time scale has been crafted; influencing the human perception of our place in Earth’s history and how our planet fits into the history of the cosmos at large. Earth’s interior can divided up into layers based on its chemical variations: the outer layer being the crust, the middle layer the mantle, and the innermost layer the core, which can furthermore be divided into an outer and an inner core. The electromagnetic field is created as a result of convection in the outer core which is fluid; composed mainly of the elements iron and nickel. Convection is the movement caused within a fluid (in this case magma) by the tendency of hotter and therefore less dense or less heavy material to rise, and colder, denser material to sink under the influence of gravity, which consequently results in transfer of heat. This convection generates electric currents which produce a magnetic field that encompasses the Earth. This process, known as geodynamo, allows the Earth’s poles to attain positive and negative charges; just like a magnet. This is reason why we can use a compass to navigate; compasses have a magnetic needle that is calibrated according to Earth’s poles.
Because we (humans) inhabit a planet characterized by magnetic poles, one positive and one negative at opposite ends, we may imagine ourselves living on a giant electromagnet. The field that encompasses our magnet protects us from solar radiation; harmful rays that come from the sun. It allows us to live, reproduce, make history, fall in love, and create art. The two poles at the edges of the giant electromagnet that we call home, reverse irregularly throughout time. At one point in history, what we consider the magnetic North Pole today, was actually the magnetic South Pole, and the magnetic South Pole was the magnetic North. The last time this happened was 780,000 years ago. If you were alive then, and facing what we call north with a magnetic compass in your hand, the needle would point to 'south.'
The cause of these irregular reversals is unknown, but here is what we do know: these irregularities are recorded in rocks and thanks to paleomagnetic data gathered from magnetic minerals within those rocks, humans have been able to make distinctions between periods of Earth’s history to create the geologic time scale and craft our own version of our planet’s past. Sediment cores taken from deep ocean floors can tell scientists about magnetic polarity shifts, providing a direct correlation between magnetic activity and the fossil or stratigraphic record. The Earth's magnetic field determines the magnetization of lava as it is laid down on the ocean floor on either side of the Mid-Atlantic Rift, right down the center of the Atlantic ocean where the North American and European continental plates are spreading apart. As the lava solidifies, it creates a record of the orientation of past magnetic fields much like a tape recorder records sound.
The same data that is recorded in the stratigraphic record and serves as the basis for the geologic time scale, can be used as a tool in assessing stratigraphic completeness. In other cases, the lack of data, may be interpreted as “missing time”; a gap in our planet’s history. It has been understood by scientists for generations that we have more gaps than physical data in the record, and that these gaps, how they occur, where they occur, and the way we interpret them, may tell us just as much about the history of the earth, as the data itself.
This leaves us with two unanswered questions: how certain are we, as a civilization of the distinctions we have made between periods of geologic history? And how complete is the story that we have crafted for ourselves? Just like many of the universe’s biggest questions, it may be more accurate to think of these as ones for which the answer cannot be found; it must be created. “History” and “Purpose” as they relate to life on Earth, are two of the very few things bigger than what science can define without the help of art, culture, and community; the fundamental things that make us human. And just like humans may choose to create a purpose for themselves and for all life on Earth, because no “purpose” is scientifically evident, we may also choose to acknowledge the gaps in our data and begin to think more accurately of our planet as a four dimensional puzzle for which we have only one percent of the pieces. And the rest, through research, communication, and innovation is yet to be discovered.
A personal story
One of my most formative experiences as a scientist was also one of my most embarrassing experiences, and it all started with a compass
When I entered university, my advisors recommended I choose a non-science major, upon seeing my high school test scores. I was not yet declared as a geology major. I wanted to prove them wrong. I had a passion for science and believed I could succeed if I were at least given a chance.
It was my first field-based geology class. We were mapping in the Texas Hill Country with only a compass, a pencil, and paper. It was a cold morning in February when I was climbing up a slippery limestone outcrop above a river with my classmates. On a particularly wet patch of rock, I tripped, and the compass fell out of my hand. It tumbled down the rock, which dipped steeply and dropped off into a very deep, cold river.
I couldn’t believe what had just happened. I dropped my compass in a river in the middle of a field mapping project. There was no way I would be able to finish the project without it. Devastated, I went to inform my professor, who was about a kilometer away.
“Can you see the compass?” he asked me.
“Just barely,” I told him.
I was prepared to pay for the compass. I had lost it. I was prepared to fail the project. It was my fault. He followed me to the outcrop and squinted his eyes to see the very bottom of the river where my compass lay. What happened next, was the most embarrassing moment of my time at university. My professor handed me his map, his compass, and his pencils, and undressed. In front of the rest of my classmates, he jumped in the river, which was nearly freezing, and swam to the bottom to get the compass. When he got out of the river, he gave me the compass, which was full of water and so foggy that it was hard to read.
That night I was so ashamed that I didn’t join my classmates for dinner. Sitting alone in my tent I thought to myself “they were right. I am not cut out for this. I cannot do science and I will never be a geologist.”
But I had to finish the project. The next day would be another full day of mapping, and I needed to use the compass. I knew the only way I would be able to complete the project is if I fixed the compass myself. And it wasn’t until that night that I truly understood how a compass works.
By the dim light of my headlamp, I removed the glass covering, cleaned it, and dried it. Then I removed the needle and did the same. When it was time to insert the needle back into the compass, I was met with a fascinating surprise; the needle seemed to almost jump out of my hand and spin into place. Without my touch or control, the compass had put itself back together. I knew theoretically that compasses had a magnetic needle, which was calibrated according to magnetic north and south, but never before had I taken apart a compass and seen the intricacies of the mechanics work before my eyes, and in my hands.
That night I went to sleep embarrassed and ashamed but also enthused in an odd way. In a single night, I had learned more about the compass than any of my classmates.
The following semester, I excelled so far in my geology studies that the very same professor who jumped in the river awarded me a scholarship to do fieldwork in Arctic Norway; a prestigious international field expedition at the University Centre in Svalbard. Two years later, I am a Board-Certified Professional Geologist by the state of Texas.