Episode 1: The Earth Calendar
Hello and welcome to Bedrock, a podcast on Earth’s earliest history.
I’m your host, Dylan Wilmeth.
In this first episode, I’ll be giving an overview of the time period covered by this podcast, and why it’s important. This show will progress forward through time starting with Earth’s formation. Along the way, I’ll interview scientists and students on the cutting edge of ancient earth research.
But before all that, I want to briefly start with a personal introduction. In 2010, I was a dinosaur kid- my life’s goal was to be a vertebrate paleontologist. But one summer’s day I took a field trip that changed my life. On the forested shores of Lake Superior, I found strange lumpy rocks that turned out to be ancient bacterial colonies- in other words, fossil pond scum. These rocks were more than four times older than the oldest dinosaur, and at once I felt the lure of Earth’s truly ancient past. Following my newfound passion, I received my PhD in Earth Sciences at the University of Southern California in 2018. I am currently a postdoctoral researcher in Brest, France. All the while, I have been studying fossil pond scum.
You might ask “Why should we care about ancient bacteria? Why should we care about old rocks at all? A rock is a rock, what’s so special?”
One of the universal traits of humanity seems to be the question: “Where did we come from?” We look at photo albums for faded images of our youthful grandparents. When we don’t have photographs, we look at cemeteries and censuses for a glimpse of family names. We take genetic tests to trace our lineage across continents before writing was crafted. And we carefully dig up bones when DNA fails us- bones of humans, primates, reptiles, and eventually fish.
But where can we turn to when bones are gone? The only things that remain, that can persist for so long, are the rocks themselves. As you can probably tell, my bias is towards rocks with evidence of life, but there are many tales of ancient Earth that take place on larger scales. In this podcast, we will see the Earth struck by objects the size of Mars, and still survive. We will see oceans of lava and glaciers that cover the entire world multiple times. And we will see a strain of life that produces a toxic, highly reactive gas that smothers the world, but eventually life adapts and evolves into completely new organisms- that gas is oxygen. For 90% of Earth’s prehistory, we would need spacesuits just to breathe. And speaking of space, governments are currently spending many dollars and many hours to find fossil pond scum on Mars, in rocks just as old and older than ones we will discuss here.
So, how ancient are we talking about?
Before I start throwing around dates of millions and billions of years, I want to give a little context. Consider this a gas-station roadmap for the grand tour we’re about to take. I will borrow a concept made popular by Carl Sagan: the Cosmic Calendar. Using this calendar, Sagan compressed the history of the universe into 365 days, with each day representing 38 million years.
Since Sagan’s Calendar tracks the entire universe’s history, Earth doesn’t show up until September! Since this podcast is about Earth, we are going to modify the calendar so that everything isn’t squished at the end. For our Earth Calendar, January 1st will NOT be the Big Bang, but the formation of Earth itself. This brings us to our first important date. If there is only one number to take away from this podcast, here it is:
The Earth is 4.6 billion years old, give or take a few decimal places down the line.
4.6 billion years ago will be our January 1st, a beginning against which all future dates can be measured. Armed with this knowledge, when you hear a news report talking about rocks 2 billion years old, you can think, “OK, that’s about halfway back in Earth’s history!”
As we move forward in the Earth Calendar, each day takes about 12 million years to pass. This number will not be on the test, I’m simply mentioning it to show the vastness of the timeframes we’re looking at. I work with rocks that are billions of years old every day, and I still find it hard to wrap my head around these numbers. It’s OK if you find all of this intimidating- my goal is not to make you, the listener, feel small- it is to show you the beauty of Earth’s past, and part of that beauty is its immensity.
The Earth Calendar, a thought experiment modeled from Sagan’s Cosmic Calendar
Image credit: Dylan Wilmeth
On our calendar, this podcast will cover Earth history from January 1st to November 19th, from 4.6 to 0.5 billion years ago. Geologists have a name for this time period- we call it The Precambrian. There are many subdivisions we will cover in later episodes. For now, Precambrian is the word of the day. I could give you a month by month preview through the calendar, but instead I’ll give you three dates as a teaser- consider these the “holidays” of the Precambrian: something special is happening, people get very excited, and there is the inevitable family argument.
Our first holiday is the end of March, 3.5 billion years ago, when we see the oldest uncontested evidence of life on Earth. Specifically, the fossils are of layered rocks that used to be ancient bacterial colonies. Life almost certainly evolved earlier, but this is our first fossil pond scum and will certainly not be the last.
Next, we fast forward to the end of June, 2.4 billion years ago, about halfway through Earth’s history. The special occasion is the rise of oxygen in Earth’s atmosphere also known as the Great Oxidation Event, or the Notorious GOE. The GOE is heralded by many changes in Earth’s chemistry, including huge deposits of rusty iron on ancient seafloors. This holiday is one of those slow-burn events that lasts for several weeks into July, and the gifts keep on giving.
Finally, we approach the end of the Precambrian, on November 19, half a billion years ago. The Precambrian ends not with a whimper, but with a bang, specifically the Cambrian Explosion. This event is not a cataclysmic eruption or impact, it is the global appearance of fossils of major animal groups, including backboned animals that will lead to us. The Cambrian Explosion doesn’t remove the pond scum that had dominated for billions of years, but the weeks of November and December will overshadow them with shell, bone, and wood, and on the last minute of December 31, brick, steel, and plastic. But those stories are for other podcasts.
After hearing all this, you might be shouting at your cell phone or computer- “We’re not covering dinosaurs or pyramids? This is a rip-off!” Now before you hit “Stop”, I have two notes of reassurance.
First, I would have said the same thing about ten years ago. I was going to dig up dinosaurs- it was my single-minded goal for as long as I could remember. And fossil beasts will always have a special place in my heart- without them, I wouldn’t be here, both career-wise and literally. This being said, you can easily find books and videos about dinosaurs and mammoths, but the 90% of earth’s history that came before is harder to find. This podcast will attempt to fill part of that void, a sample platter of the great Precambrian buffet.
Finally, while we won’t be talking about kings, pyramids, or even Neanderthals, there will be people in this story. These are people who sweat in the sun hammering rocks in South Africa, Australia, India, and Canada. These are people who spend many nights in the laboratory, perfecting intricate chemical and biological experiments. These are also people who relax in bars on Friday evenings, laughing and singing karaoke with everyone else. These are the scientists who investigate the Precambrian world, and it will be a pleasure to introduce them, their stories, and their research to you.
Over the next few episodes, I will give you the mental toolkit you need before we set out on this great adventure. And I don’t know about you, but every road trip needs snacks. So next episode, break out your oven mitts and pressure cookers, because I’m going to give you three recipes for making a rock.
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Thank you for listening to Bedrock, a part of Be Giants Media. As the show takes off, I would love to hear your input on style, topics, and people to interview- you can drop me a line at bedrock.mailbox@gmail.com. See you next time!
Images:
Cathédrale Notre-Dame de Strasbourg from Wikimedia Commons, photo by Gzen92
https://commons.wikimedia.org/wiki/File:Cathédrale_Notre-Dame_-_intérieur_-_horloge_astronomique_-_détail_(Strasbourg).jpg
Earth Calendar by Dylan Wilmeth
Music:
Taking it In by Michael Brandon
Their Arrival by Emmett Cooke
The Planets: Jupiter by Gustav Holst, performed by the United States Air Force Heritage of America Band https://commons.wikimedia.org/wiki/File:Holst_The_Planets_Jupiter.ogg