#geologic time scale

Oh my god I love it!! Yes it is totally cool!!

Deep time is not an easy thing to try and comprehend and it certainly doesn’t help when there’s all these crazy names being thrown at you. Let’s take a moment to break it down and really understand what we are seeing. The largest unit of geochronologic time is an eon. There are four formally defined eons: the Hadean, the Archean, the Proterozoic, and the Phanerozoic. The Hadean Eon is the oldest eon going from 4.6-4 Ga years ago. Its name is derived from the Greek god, Hades in reference to the still molten surface of the newly formed planet.

Following the Hadean Eon is the Archean Eon. This eon went from 4-2.5 Ga years ago. As mentioned in my Barberton Greenstone Belt video two weeks ago, this eon saw the creation of oceans and mountains as well as the appearance of the first living organisms known as stromatolites which would put oxygen into the atmosphere. Archean means “beginning or origin” which is fitting.

Next came the Proterozoic Eon. Lasted from 2.5 Ga-545 Ma. During this eon, the atmosphere became oxygenated, there were several glaciations, and the first eukaryotes evolved represented by the Ediacaran Biota. The name Proterozoic means “before life” because initially, fossils hadn’t been found until the Cambrian Period.

The last eon which we are currently in is the Phanerozoic Eon. It means “visible life” which makes sense as most living organisms have existed within this eon.

Okay, eons make sense? Excellent. Eons are broken down into eras. Now the Hadean is not broken into eras simply because the only evidence of this eon are detrital zircons in Australia.

The Phanerozoic Eon is the current eon and most of you are probably familiar with its eras: The Paleozoic Era, the Mesozoic Era, and the Cenozoic Era. These names mean “old life”, “middle life”, and “new life” respectively.

Eras are then split into periods. Like the Hadean before it, there isn’t enough evidence to split the Archean eras into periods. Again, we will use the Phanerozoic eras to show the break down starting with the Paleozoic.

The Paleozoic Era is split into six periods: the Cambrian Period,

the Ordovician Period,

the Silurian Period,

the Devonian Period,

the Carboniferous Period

and the Permian Period.

These will be discussed in more detail later on down the road. I have already made posts on the Cambrian and the Ordovician Periods and this month is all about the Silurian Period.

The Mesozoic Era is split into three periods of which most people know the names: The Triassic,

the Jurassic,

and the Cretaceous Periods.

Each of these will be discussed in detail further down the road as well.

The Cenozoic Era is also split into three periods: The Paleogene Period,

the Neogene Period,

and the Quaternary Period.

These will also be discussed in detail later.

Periods are further broken down into epochs. There are no formal epochs outside of the Phanerozoic Eon. Some early Paleozoic periods also do no have formal epochs. Many such as the Triassic and Jurassic Period are split into Early, Middle and Late. Strangely, the Cretaceous is only split into Early and Late though I think an argument could me made to create a middle.

The most well-known epochs are those of the Cenozoic Era. The Paleogene Period is split into three epochs: the Paleocene Epoch meaning “old dawn”,

the Eocene Epoch meaning “dawn”,

and the Oligocene Epoch meaning “few new”.

The Neogene Period is split into two epochs: the Miocene Epoch meaning “less new”

and the Pliocene Epoch meaning “more new/recent”.

The Quaternary Period is split into two epochs as well: the Pleistocene Epoch meaning “most new/recent”

and the Holocene Epoch meaning “whole new” and is the epoch we are currently in.

Epochs can then be broken down into still smaller categories called ages. For example, the Late Jurassic Epoch is broken up into three ages: Oxfordian Age, Kimmeridgian Age and Tithonian Age.

Now let’s put all these, eons, eras, periods, epochs, and ages into perspective. Let’s pretend Earth’s current lifespan is a clock. At 12:00, the Earth’s crust forms (Hadean Eon). At 2:10, the oldest rocks are preserved (Archean Eon). At 3:17, the first bacteria appear (Proterozoic Eon). At 11:52, the Cambrian Explosion occurs. At 11:53, first plants and fish. 11:54, first insects. 11:55, first reptiles and amphibians. 11:56, Mesozoic Era begins. 11:57, first dinosaurs, mammals, and birds. 11:59 Cenozoic Era.

Need a different visual? Try a calendar. The Hadean starts in January and ends halfway through February where the Archean picks up. The Archean lasts until halfway through June. From there, the Proterozoic starts and doesn’t end until about Thanksgiving. The Paleozoic Era then goes until about a week before Christmas. The Mesozoic covers Christmas to the December 30. New Year’s Eve represents the Cenozoic Era.

Thanks for coming to this lesson and make sure to tune in tomorrow for some fun trivia! Fossilize you later!

By: @zoe248

Ok, so I just started rewatching a prehistory documentary I used to love as a kid. It's about the whole geologic timeline and the evolution of all life on earth over it's lifespan.

I could barely get through the first 3 minutes without bursting into tears. Oh my god. I don't know what it is but these past few weeks I've learned that apparently evolution makes me super emotional?? I *genuinely* cannot think about concepts like the mass extinctions or any extinct ancient creature without feeling a lil pang in my chest. Up until now I failed to realize how formative this facet of science was to me growing up and it's all hitting me now lol.

What's weird is that geology didn't even occupy my headspace at ALL after I was like, 12 until a month ago. It's like I'm returning to something old that I used to love, before all the internet and all the fandom stuff I'd end up getting into in my teens later. It's so wacky.

I started reading a book on trilobites yesterday and also got emotional at the author writing about the ancient rocks and formations. I'm crying at rocks chat, ROCKS. It's so over for me but also we're so back.

This is so weird and I've never felt anything like it... sniff sniff... look at these stupid "try the bites" or whatever they're called

Figure 1:  Baculites fossil from the Bayet Collection with L. W. Stilwell label.

Why did a wealthy European baron seek out a Dakota Territories fossil dealer in the winter of 1889?    This post is the first of a four-part series on renowned 19th century fossil collectors Baron de Bayet of Brussels and Lucien W. Stilwell, and their connection to the Carnegie Museum of Natural History.  Bayet assembled one of the great private fossil collections in Europe.  In 1903, Andrew Carnegie bought the 130,000-fossil collection and had it shipped from the Port of Antwerp in Belgium across the Atlantic to the United States.  The purchase garnered headlines in newspapers across Europe and in the United States and launched Carnegie’s fledgling museum onto the world stage.  Thanks to the archival materials purchased by Carnegie as part of the Bayet deal, the relationship between Baron de Bayet and Lucien W. Stilwell provides a glimpse into how the Carnegie Museum of Natural History and other institutions built their collections.   In part one, we consider what forces may have prompted Bayet to assemble a large collection of fossils in the first place.

The Pathway to Fossil Collecting Travelled Through the Principles of Stratigraphy and Geology

From the late 17th century until the early 19th century, collecting fossils was a hobby of gentlemen farmers and naturalists.  Some of these collectors developed fundamental principles of geology and stratigraphy through observations and deductive reasoning, as to how rock layers, or strata, are formed, fully earning credentials as scientists.  For example, in the 17th century physician Nicolaus Steno’s (1638 – 1686) observed simple patterns in strata during his walks through the hills of northern Italy.  The four Laws of Stratigraphy he proposed are the law of superposition, the law of original horizontality, the law of cross-cutting relationships, and the law of lateral continuity.

The principles of stratigraphy were later interpreted by James Hutton (1726-1797), a Scottish geologist, to formulate his Doctrine of Uniformitarianism in 1785.  This line of thinking assumed that the same natural laws and processes that currently operate in the universe had always operated in the universe and applied everywhere in the universe.  Hutton’s Uniformitarianism included the gradualistic concept that “the present is the key to the past”.  

William ‘strata’ Smith (1769 – 1835), considered the Father of Stratigraphy was a geologist and engineer who uncovered fossils from strata as he worked to build a water canal from Oxfordshire, England to the Thames River at London.  In 1815 he made the first color geologic map of England, Wales, and part of Scotland, a document that developed from his identification of strata based on fossil taxa within the rock layers.  His careful tracking suggested that fossil organisms, both faunas and floras, recorded in each geologic formation succeed one another in a definite and recognizable order, a principle summarized as the law of faunal succession.  

Smith’s map led, in 1822, to geologists William Conybeare and William Phillips naming the Carboniferous Period for the younger (coal beds) and older (limestones) boundaries respectively for this ancient unit of geologic time.  Because a single time period could not rest alone in any record of Earth history, the pioneering work of Conybeare and Phillips, Smith, Hutton, and Steno led eventually to the establishment of the Geologic Time Scale, a framework of three unimaginably long Eras, the Paleozoic, Mesozoic, and Cenozoic, for studying the evolution of life as preserved in the fossil and rock record over Earth’s 4.6-billion-year history.  Within the Geologic Time Scale the Carboniferous Period is one of seven periods of the 290 million years that represent the Paleozoic Era.

As these principles of geology grew in acceptances, Charles Lyell (1769 -1875) an English field geologist who traveled extensively throughout Europe and North America, wrote a three-volume Principles of Geology (1830 – 1833), a work that Charles Darwin read during his Voyage of the Beagle (1831 – 1836).  Darwin’s Theory of Evolution as written in his The Origin of Species by Means of Natural Selection – or the Preservation of Favored Races in the Struggle for Life circa 1859, was influenced by the geology and stratigraphy ideas put forth in the Principles of Geology.

Museums Emerged

Amateur fossil collectors such as Stilwell and Bayet perhaps recognized opportunities to supply and acquire fossils to satisfy demand for fossils by museums and universities across Europe and the United States.  The first museum to become established in Europe was the Muséum national d'histoire naturelle in Paris, France in 1793, followed by the Museum für Naturkunde Berlin in 1810.   Museums in Belgium, London and Austria followed.

In the United States, the Lewis and Clark Expedition (1804 – 1806), mandated by President Thomas Jefferson, was the first U.S. government expedition to explore the unknown territory of the Louisiana Purchase in search of minerals, fossils, and indigenous artifacts.  Co-led by Merriweather Lewis (1774 – 1809) and William Clark (1770 – 1838), the expedition collections were deposited at the Academy of Natural Sciences of Philadelphia, now known as the Academy of Natural Sciences of Drexel University.  Soon, other university museums came into existence such as “The Louis Agassiz Museum of Comparative Zoology", of Harvard University in 1859, and the Peabody Museum of Natural History at Yale University in 1866.   The United States government established the Smithsonian Museum of Natural History in 1866.  Before long, private institutions such as the American Natural History Museum in New York City, the Field Museum of Chicago, and Carnegie Museum appeared on the scene.

As museums hired scientific staff, rivalries between experts at different institutions developed.  By the 1870’s, paleontologists Edward Drinker Cope, of the Academy of Natural Sciences in Philadelphia, and O.C. March, of the Peabody Museum at Yale University, began a two-decade competition to outdo each other in a battle to collect and name as many vertebrate fossils as possible.  Their exploits are often referred to as “the Bone Wars” (Rea 2001).    In 1874, O. C. Marsh arrived in the Dakota Territories.   Word of the exotic sea creatures from the Western Interior Seaway and mammals from the Oligocene Period reached Europe, leading the Baron de Bayet to contact Lucien W. Stilwell for his assistance in acquiring “one of every species and variety.”

Next:   Lucien W. Stilwell arrives in Deadwood Dakota Territories, a town known for gold, gambling and lawlessness.  

Imagine the nearly unimaginable: 4.6 billion years. That’s how old the Earth is — a mind-boggling length of time. And to measure it, scientists use special terms, most of which focus on the planet’s changing geology. That’s why, in fact, it’s known as geologic time.

To grasp just how old Earth is, imagine fitting its entire history into one calendar year. If Earth formed on January 1, the earliest primitive life (think algae) wouldn’t appear until March. Fish first swam onto the scene in late November. Dinosaurs stomped around from December 16 until December 26. The first modern humans — Homo sapiens — were real late-comers. They didn’t show up until just 12 minutes before midnight on New Year’s Eve.

Almost as mind-boggling is how geologists figured this all out. Like chapters in a very, very thick book, layers of rock chronicle Earth’s history. Put together, the rock records the long saga of life on Earth. It shows how and when species evolved. It also marks when they thrived — and when, over millions of years, most of them went extinct.

Explainer: How a fossil forms

Limestone or shale, for example, may be the remains of long-gone oceans. These rocks contain traces of life that existed in those oceans over time. Sandstone might once have been an ancient desert, where early land animals scurried. As species evolve or go extinct, the fossils trapped in the rock layers reflect these shifts.

How to track such a long, complex history? Using dazzling detective skills, geologists created a calendar of geologic time. They call it the Geologic Time Scale. It divides Earth’s entire 4.6 billion years into four major time periods. The oldest — and by far the longest — is called the Precambrian. It is divided into Eons known as the Hadean (HAY-dee-un), Archean (Ar-KEY-un) and Proterozoic (Pro-tur-oh-ZOE-ik). After the Precambrian come the Paleozoic Era and Mesozoic Era. Last but not least is the Cenozoic (Sen-oh-ZOE-ik) Era, the one in which we live. The Cenozoic started about 65 million years ago. Each of these Eras, in turn, are divided into increasingly smaller divisions known as Periods, Epochs and Ages.

Unlike months in a year, geologic time periods aren’t equally long. That’s because Earth’s timeline of natural change is episodic. That means changes happen in spurts, rather than at some slow and steady pace.