Marking out the Earth's history - some recent drama llama

[lpetrich]

Stratigraphy is the mapping out of the Earth's history over its rocks and other deposits, and for the most part, it has been a background sort of endeavor, without much controversy. There has been some recent drama llama in it, which I will be getting to.

As geologists studied our planet's rocks in the late 18th century, they came to recognize that they were organized in a layer-cake sort of fashion, with each layer having characteristic fossils, and with the layers having the same order almost everywhere. The exceptions were due to geological effects like some rocks getting thrust over some other rocks. These layers are called strata and the science of them stratigraphy.

The first attempt at division was Primary, Secondary, Tertiary, and Quaternary (1, 2, 3, 4). The Primary later became the Paleozoic Era ("old life"), the Secondary the Mesozoic Era ("middle life") and the Tertiary and Quaternary the Cenozoic Era ("recent life"). All three are the Phanerozoic Eon ("apparent life"), with the Cryptozoic Eon ("hidden life") before it, now called the Precambrian Eon.

The eras are divided into periods, with the Paleozoic Era starting with the Cambrian Period and ending with the Permian Period. Both of them are named after locations whether rocks from those times can be found. The Cambrian is named after Cambria, a Latinization of Cymru, Welsh for Wales. The Permian is named after a district in Russia. Some periods are named after characteristic contents. Before the Permian was the Carboniferous, named after its coal deposits, and the last period of the Mesozoic is the Cretaceous Period, named after Britain's Dover chalk. Before it is the Jurassic Period, named after the Jura mountains of France and Switzerland. Before that was the first Mesozoic Period, the Triassic, named after three distinctive layers of rock.

The Cenozoic's divisions have a rather complicated history, with its periods being the Tertiary and Quaternary (most of it, the last few million years), the Paleogene ('old born?") and Neogene ("new born?") (2/3, 1/3 of it), or else 6 or 7 smaller periods. But geologists have decided on this division:

Split the Tertiary into the Paleogene and Neogene Periods, with the Quaternary Period following them, and with the 6 or 7 smaller periods turned into epochs inside these periods. Here goes:

• Paleogene: Paleocene ("old recent"), Eocene ("dawn recent"), Oligocene ("a little recent")
• Neogene: Miocene ("less recent"), Pliocene ("more recent")
• Quaternary: Pleistocene ("the most recent"), Holocene ("all recent")

Geologist Charles Lyell, who marked out that last one, named it "Recent", using the English word, but his successors have preferred to name it much like its predecessor epochs.

Most recently, the International Commission on Stratigraphy has decided on a division of the Holocene Epoch into ages, as geologists call an epoch's subdivisions.

• Greenlandian Age, beginning 11700 years before 2000 CE, when the Holocene began, at the end of the Younger Dryas cold period. Named after the source of some ice cores that span the last 105,000 years of Earth history.
• Northgrippian Age, beginning 8326 years before 2000 CE, at the beginning of an unusual cold period in the Northern Hemisphere. Named after the North Greenland Ice Core Project, a drilling project that obtained those ice cores.
• Meghalayan Age, beginning 4200 years before 1950 CE, at the beginning of a cold period and a big drought that badly hurt several early large-scale societies. Named after Meghalaya State, India, where a stalagmite marker for it was found.

Collapse of civilizations worldwide defines youngest unit of the Geologic Time Scale, ICS chart containing the Quaternary and Cambrian GSSPs and new stages (v 2018/07) is now released!

So we live in the Meghalayan Age of the Holocene Epoch of the Quaternary Period of the Cenozoic Era of the Phanerozoic Eon.

 

[lpetrich]

 8.2 kiloyear event - the Greenlandian - Northgrippian boundary - a phase of cooling and drought that lasted for the next 2 to 4 centuries.

Likely caused by a former glacial lake that rather suddenly drained into the Atlantic Ocean. It was likely Lake Agassiz - Ojibway in southern Canada at the edge of the Laurentide Continental Glacier of back then. It would have broken through some glacial ice and rushed into the St. Lawrence River and then the North Atlantic Ocean. It was something like the giant floods of the Columbia River caused by the repeated breaking of a glacier that had dammed up Glacial Lake Missoula in the late Pleistocene.

 4.2 kiloyear event - the Northgrippian - Meghalayan boundary - a phase of cooling and intense drought. It happened within recorded history in Egypt and Mesopotamia, likely calling the fall of the Egyptian Old Kingdom and the Mesopotamian Akkadian Empire. It also affected India and China.

Its cause is less clear.


Now for the drama llama. Geology’s Timekeepers Are Feuding - The Atlantic has the story. It is about the Anthropocene ("human recent"), a proposed geological-timescale division. It was entirely omitted from this recent division of the Holocene, something that some geologists consider a slight.

The Anthropocene supporters have critics who claim that those supporters do not have good stratigraphic work that supports their position. They also do not agree on when the Anthropocene should start.

Some 6,000 - 4,000 years ago? That is when as farmers started turning large amounts of land into cropland.

1492? The beginning of European explorers and colonists spreading in a massive way themselves and their domestic animals and plants and their diseases.

1800? The beginning of the Industrial Revolution, with its massive consumption of fossil fuels and resource extraction.

1950? The beginning of car culture in the US and other advanced industrialized nations, with greatly increased consumption of fossil fuels and spewing of greenhouse gases.

But why Anthropocene? Why not Capnocene ("smoke recent")? That would be in honor of burning of fossil fuels.