Everything Everywhere Daily: History, Science, Geography & More - The Geologic Timeline

Episode Date: September 8, 2021

The Earth is pretty old. Our current, best estimate is that it is 4.54 billion years old, plus or minus 50 million years. Since then, however, a lot has happened. To help clarify the Earth’s timeline, geologists have divided the Earth’s history into various eras and periods. Each division of time represents a change in something, which happened on the planet. Learn more about the Earth’s history and geologic time scales, on this episode of Everything Everywhere Daily. Learn more about your ad choices. Visit megaphone.fm/adchoices

The Earth is pretty old. Our current best estimate is that it's 4.54 billion years old, plus or minus 50 million years. Since the Earth formed, however, a lot has happened. To help clarify the Earth's timeline, geologists have divided the Earth's history into various errors and periods. Each division of time represents a change in something which happened on the planet. Learn more about Earth's history and the geologic timescales on this episode of Everything everywhere daily. Do you ever climb into bed ready to sleep only to have your mind start racing the

moment your head hits the pillow? Thoughts bouncing around, replaying the day or jumping ahead to tomorrow? That is exactly why Catherine Nikolai created Nothing Much Happens. Each episode is a gentle, cozy bedtime story where, well, nothing much happens. No drama, no tension, nothing you need to follow closely. Just soft narration, calming repetition, and soothing sensory details designed to help your mind slow down and your body relax. It's not about entertainment, it's about rest. And millions of listeners around the world use it every night to quiet their thoughts and finally fall asleep. If you've ever struggled to shut your brain off at night, this might be exactly what you've been missing. You can listen to Nothing Much Happens wherever you get your

podcasts. Episodes are every Monday and Thursday. This episode is sponsored by the tourist office of Spain. In Spain, you can find accommodations like you can find everywhere else, hotels of all luxury levels and even hostels. However, you can also find something in Spain that you can't find everywhere. Peradores. A peridore is a luxury accommodation, usually in a refurbished historic building like a monastery or a castle, or in a modern building with a really great view. There is an official network of over 90 Peradores scattered all over the country in every region. In my many trips to Spain, I've stayed at several Peradores, and it's always a unique experience that adds an extra cultural element to every trip. I've stayed at ones in Guadalupe, Caseres, and in Costa Brava.

You can research visiting one of the many pedidores in Spain before your next visit by going to Spain.info. Once again, that's Spain. Info. The Earth is so old that to make sense of its history, geologists have come up with divisions. These divisions are very broad and cover millions to billions of years, depending on what the division is. Each division also has subdivision, that they themselves can be further subdivided. The three primary temporal divisions of Earth's history are eons, eras, and periods. An eon is a very broad definition of history,

and there's really only been three eons. The Arcan, which goes from the formation of the Earth to about 2.5 billion years ago. The Proterozoic, which goes from 2.5 billion years ago to about 540 million years ago, and the fanerozoic, which goes from 540 million years ago to today. There is also sometimes a fourth ion called the Hedain, which would have been the formation of the Earth to about four billion years ago, but it's really hard to study that period

by itself, so it's often just lumped with the Archaean. I actually studied geology and geophysics for several years, and the use of eons seldom came up. Occasionally you would hear about the Archaean, but other eons are so broad that they're just generally not useful. The Archaean is the period where the continents started to form, and the very simplest life began. The Proterozoic is the ion where oxygen appeared in the atmosphere, and up to the beginning of complex multicellular life. In the Archaean and the Proterozoic, there is little to nothing

in the way of fossils, because there was nothing that could be fossilized yet. There are some fossilized stromatolite beds, which were mats of bacteria, but that's about it. The rest of this episode will focus on the Phanerozoic ion. That's where most geologic research is done, and it's where all the fossils are. The Phanerozoic is divided up in three eras, the Paleozoic, the Mesozoic, and the Senezoic. The first period in the Paleozoic is the one you might have heard of, the Cambrian. The Cambrian is noted for the sudden appearance of complex life forms and animals in the fossil record. This is known as the Cambrian explosion. Here is where you'll see many of the trilobites, which are really common fossils. In fact, the appearance of

trilobites pretty much defines where the Cambrian appears in the geologic record. All complex life that we know of in the Cambrian was in the sea. Nothing yet had come on to land. Of all the periods I'll be going over, this is one of the most important to have a grasp on. It spans about 55 million years, from 540 million years ago to about 485 million years ago. After the Cambrian comes the Ordovician period. It lasted for 41 million years and went from 485 million years ago to about 444 million years ago. It's noted for its continued biodiversity diversification. The fish first appeared during this period and probably the first fish with jaws. These were the first vertebrate animals. There still

wasn't any animal life on land yet in the Ordovician that we know of. There were lots of volcanoes and meteors during this period as well. By some estimates, over 100 times the number of meteor strikes that the Earth experiences today. The next period is the Silurian. It goes from 440 million years ago to 419, million years ago. What separates the Ordovician and the Silurian is the Ordovician Silurian extinction event. This is the first of the major extinction events in Earth's history and the second largest in terms of the number of species that disappeared from the fossil record. The Silurian sees the appearance of the very first vascular plants on land, as well as the first

arthropod-type creatures on land. I should also note that as we get closer to the present, the information we have becomes better, the divisions in time become more precise, and there are more subdivisions, most of which I'm not going to be going into. After the Silurian comes the Devonian, which extended from 419 million years ago to 359 million years ago. If you were to travel back in time to the Devonian, you'd probably at least recognize the land as being Earth. Life on land had exploded in biodiversity. You would see actual forests and seed-bearing plants. This was also a heyday for fish, and there was a large increase in the number of fish species. Ammonites, which are popular in common fossils with a spiral shell,

appeared here as well as the first tetrapods, which were animals with four legs. If you ever envisioned a fish walking onto dry land, well, it didn't quite work like that, but it would have happened in the Devonian. Following the Devonian came the Carboniferous. It lasted from 358.9 million years ago to 298.9 million years ago. As the name would suggest, the Carboniferous period gets its name from Carbon. In particular, many of the coal beds which are found around the world. The most common land animal during this period were amphibians.

You also find the very first reptiles appearing at the very end of this period. Insects also saw a radical increase in diversification, including species like a dragonfly with a 79 centimeter or 28-inch wing span. The high oxygen levels allowed for such huge insects. There would literally be impossible today because insects don't have lungs. The Carboniferous period saw the highest oxygen. oxygen levels in Earth's history, in fact, reaching 35%. It also saw the formation of the supercontinent, Pangaea. At the end of the Carboniferous, there occurred what was known as the

Carboniferous Rainforest Collapse. This created most of the coal beds we know today, and it also created islands of life. Prior to the collapse, most landlife was widespread all over Pangaea. The last of the Paleozoic periods is the Permian. It lasted from 298.9 million years ago to 252.17 million years ago. The Permian saw the rise of amniotes, or what's known as higher-level vertebrates. All mammals, reptiles, and birds belong to this class. The thing that really defines the Permian is how it ended. The Permian Triassic extinction was the largest mass extinction event in the Earth's history. 81% of all aquatic species died, and 70% of all land species. There is a very clear layer in the geologic record known as the PT layer, where on one side you can find

Permian fossils, and on the other side you can't. And this is where all the trilobites ended. The Permium Triassic extinction was believed to be caused by a massive volcanism event known as the Siberian traps. Over a two million year period, it covered most of what is today central Siberia with basalt rock and radically change the Earth's atmosphere. With the end of the Paleozoic, we now start to get into periods that you might be a bit more familiar with. The first of these three periods of the Mesozoic is the Triassic. The Triassic went from 252.1 million years ago to 201.3 million years ago. Life recovered from the Permium Triassic extinction, and the primary land life form that developed were called archosaurs. They can roughly be

considered reptiles. You also saw the first flying vertebrates called petrosaurs, and in the late Triassic you saw the first animals that we would call dinosaurs. There were also some of the very earliest ancestors of what we would call mammals. During the Triassic, Pangaea broke up into Laurasia in the north and Gondwana in the south. After the Triassic came the Jurassic, which I'm sure everyone is familiar with. The Jurassic went from 201.3 million years ago to 145 million years ago. The Tyrasic and Jurassic were separated by another major extinction event, known as the Tyrasic and Jurassic extinction event. The cause of this extinction isn't as obvious, and there's still a lot of debate about it. It could have been a meteor strike, or it could have been more

volcanism. During the Jurassic, dinosaurs became the dominant land animal. However, I have to point out that most of the dinosaurs in the movie Jurassic Park are not from the Jurassic period. They are mostly from the next period, the Cretaceous. It is the last period in the Mesozoic and the longest. It lasted from 145.5 to 66 million years ago. Dinosaurs were still the dominant land animal and flowering plants began to dominate plant life. The late Jurassic and Cretaceous saw the period of the largest dinosaurs with species like the Tyrannosaurus rex. This period was relatively warm with forests reaching all the way up to the polar regions.

The Cretaceous ended with a bang, literally. The Cretaceous Paleogene or Cretaceous tertiary extinction was another mass extinction. Unlike the previous ones, this one was a little more sudden. The current theory which is now widely accepted is that the end of the Cretaceous came about about with a meteor impact in what is today the Yucatan Peninsula of Mexico. There's a very clear boundary in the rock layer where you can see increased eridium, which is much more common in meteors than it is on the rest of the earth. It wiped out all of the large megafauna on land.

After the extinction, there were no land animals weighing over 25 kilograms on Earth. After this extinction, the current era, the Cenozoic began, and the first period was known as the paleogene. It extended from 66 to 23 million years ago. Mammals rose to prominence during this period. While they had always been around the last few periods, they were rather minor. Now they were able to dominate and diversify. You saw the rise of large mammals as well as aquatic mammals.

One type of dinosaur which did survive was flying dinosaurs. They became what we call birds, and there was also a huge increase in bird diversity during this period as well. The continents were beginning to move into the places where they are today. Temperatures overall cooled, but there were some periods with very warm temperatures along the way. The next period was the Neogene, which went from 23 million years ago to 2.58 million years ago, and you'll notice that the dates are getting far more precise as we get closer to the present. North and South America joined up during this period, and there was also

considerable cooling. The late Neogene saw the beginning of ice ages. India was colliding with Asia, forming the Himalayan mountains. Sea levels fell, creating land bridges, which connected Asia and North America. The Poles also started developing ice caps during this period. Many mammals that we would be familiar with today, or at least close relatives of them, appeared during this period. The final period is the one that we're in today, the quaternary. This extends from 2.588 million years ago to the present.

This is basically the entire time that covers the period where we can point to species that were ancestors of humans. This period is probably best defined by the series of glaciersions that occur during this period. I haven't talked about epochs, which are subdivisions of periods, but it's worth it for the quaternary. The early quaternary is known as the Pleistocene. It went from 2.5 million years ago to 11,700 years ago. Starting 11,700 years ago, we entered the Holocene epic. The event which divides the Pleistocene from the Holocene epic is the end of the last Ice Age and the end of the younger Dryest.

The Under Dryas is a really important period of human history and one that I have scheduled to do a future episode on. The start of human agriculture also sort of corresponds with the beginning of the Holocene. There won't be a quiz at the end of this episode. You don't need to worry about knowing all of these different periods, although I had to do exactly that when I was studying geology. But I think it's helpful for everyone to have a rough idea of the Earth's timeline. You should approximately be able to know some of the major events. For example, the Earth formed 5.4 billion years ago. Complex life appeared 550 million years ago. 440 million years ago, things moved on land. The dinosaurs went extinct about 66 million years ago,

and the first human ancestors appeared about 2 million years ago. This is just one of the many things I think a reasonably knowledge person should know off the top of their head. As I said, you don't need to know everything on the timeline, but you should know where to stick the most important pins. The associate producers of Everything Everywhere Daily are Peter Bennett and Thor Thompson. I want to give a big thank you to everyone who has supported the show over at Patreon and who's left a review on the various podcast sites. The show just keeps on growing. Podcasting is unlike anything else in the internet.

There's no algorithm and there isn't one company that controls everything. That means I can't try to game an algorithm to grow my audience. I just have to try to put out a good show every day and hope that everyone who listens will tell their friends about it. Remember, if you leave a review online or ask me a question via email or social media, I'll read it on the show.