path: root/CosmicCalendar.hs

{-# OPTIONS_GHC
  -Wall
  -Wno-unused-imports
  -Wno-unused-top-binds
  -Wno-name-shadowing
#-}
{-# language NoImplicitPrelude #-}
{-# language RecordWildCards #-}
{-# language FlexibleContexts #-}
{-# language TemplateHaskell #-}
{-# language ViewPatterns #-}
{-# language OverloadedStrings #-}
{-# language QuasiQuotes #-}

module CosmicCalendar where

import Rebase.Prelude
import qualified Rebase.Prelude as Prelude
import Control.Lens hiding ((<|))
import Data.Foldable (toList)
import Data.Ratio
import Text.Printf
import Data.Time.Calendar.OrdinalDate
import Data.Time.LocalTime
import Control.Monad.RWS
import Data.Time.Calendar.OrdinalDate
import Data.Text.Format.Numbers
import NeatInterpolation
import Data.Text (Text)

import Rebase.Data.Map.Strict (Map)
import qualified Rebase.Data.Map.Strict as Map

-- 13.787±0.020 billion years.  Source: https://en.wikipedia.org/wiki/Age_of_the_universe#cite_note-Planck_2018-2
ageOfUniverseInYears :: Integer
ageOfUniverseInYears = 13787 * 1000 * 1000

-- The point of the cosmic calendar is to mentally visualize or model the scale
-- of cosmic/geologic/evolutionary events using the existing internal mental
-- model of the year. This internal mental model of the year is NOT a 365.2422
-- day earth rotation, but a 365 day calendar year.
--
-- In order to make the math of the calendar work out, the functions that look
-- up calendary entries (and take as input the LocalTime) must check for leap
-- year, and subtract one day from the input if it is later than February.
daysPerYear :: NominalDiffTime
daysPerYear = 365 -- NOT 365.2422

lengthOfDay :: NominalDiffTime
lengthOfDay = 24 * 60 * 60

lengthOfYear :: NominalDiffTime
lengthOfYear = daysPerYear * lengthOfDay

ageOfUniverse :: NominalDiffTime
ageOfUniverse = fromIntegral ageOfUniverseInYears * lengthOfYear

data CalendarEntry = CalendarEntry {
  calBeginTime :: NominalDiffTime,
  calEndTime :: Maybe NominalDiffTime,
  calTitle :: Text,
  calSubtitle :: Text,
  calDescription :: Text,
  calReferences :: Text
} deriving (Show)

-- TODO: Encode the input times like so:
--
-- data CosmicTime = YearsAgo Rational | YearsAfterBigBang Rational | YearsBCE Rational | YearsCE Rational
--
-- The absolute time values (YearsBCE and YearsCE) will be computed using the
-- year at program start:

currentYear :: Integer
currentYear = unsafePerformIO $ getZonedTime <&> toGregorian . localDay . zonedTimeToLocalTime <&> view _1

theCalendar :: Map NominalDiffTime CalendarEntry
theCalendar = Map.fromList $ map (\x -> (calBeginTime x, x)) theCalendarList

years :: Rational -> NominalDiffTime
years = (* lengthOfYear) . fromRational

yearsAgo :: Rational -> NominalDiffTime
yearsAgo (fromRational -> n) = lengthOfYear * (1 - (n / fromIntegral ageOfUniverseInYears))

afterBigBang :: NominalDiffTime -> NominalDiffTime
afterBigBang = (/ ageOfUniverse) . (* lengthOfYear)

thousandYears :: Rational -> NominalDiffTime
thousandYears = years . (* 1000)

millionYears :: Rational -> NominalDiffTime
millionYears = thousandYearsAgo . (* 1000)

billionYears :: Rational -> NominalDiffTime
billionYears = millionYearsAgo . (* 1000)

thousandYearsAgo :: Rational -> NominalDiffTime
thousandYearsAgo = yearsAgo . (* 1000)

millionYearsAgo :: Rational -> NominalDiffTime
millionYearsAgo = thousandYearsAgo . (* 1000)

billionYearsAgo :: Rational -> NominalDiffTime
billionYearsAgo = millionYearsAgo . (* 1000)

yearStart :: LocalTime -> LocalTime
yearStart (LocalTime d _) = LocalTime d' t'
  where
    d' = fromGregorian y 1 1
    t' = TimeOfDay 0 0 0
    (y, _, _) = toGregorian d

localTimeToYearElapsed :: LocalTime -> NominalDiffTime
localTimeToYearElapsed t = t `diffLocalTime` yearStart t

getPreviousCalendarEntry :: LocalTime -> Maybe CalendarEntry
getPreviousCalendarEntry (localTimeToYearElapsed -> t) = snd <$> Map.lookupLT t theCalendar

getCurrentCalendarEntry :: LocalTime -> Maybe CalendarEntry
getCurrentCalendarEntry (localTimeToYearElapsed -> t) = snd <$> Map.lookupLE t theCalendar

getNextCalendarEntry :: LocalTime -> Maybe CalendarEntry
getNextCalendarEntry (localTimeToYearElapsed -> t) = snd <$> Map.lookupGT t theCalendar

theCalendarList :: [CalendarEntry]
theCalendarList =
  [
    CalendarEntry 0 Nothing "The Big Bang" "The universe begins" "" "",
    CalendarEntry (370 & thousandYears & afterBigBang)
                  Nothing
                  "Recombination"
                  "The universe becomes transparent"
                  recombinationDescription
                  recombinationReferences,
    CalendarEntry (13.4 & billionYearsAgo) Nothing
    "The first observed star"
    ""
    "First Light Viewed Through the Rich Cluster Abell 2218"
    "https://sites.astro.caltech.edu/~rse/firstlight/",
    CalendarEntry (4.6 & billionYearsAgo) Nothing
    "Formation of the Sun"
    "The formation of the solar system begins"
    "The formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud.[1] Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed."
    "https://en.wikipedia.org/wiki/Formation_and_evolution_of_the_Solar_System",
    CalendarEntry (4.54 & billionYearsAgo) Nothing
    "Formation of Earth"
    ""
    earthDescription
    "https://en.wikipedia.org/wiki/History_of_Earth#Solar_System_formation",

    CalendarEntry (3.4 & millionYearsAgo) Nothing
    "First Stone Tools"
    "Mode I: The Oldowan Industry"
    [text|
    (Stones with sharp edges.)

    The earliest known Oldowan tools yet found date from 2.6 million years ago, during the Lower Palaeolithic period, and have been uncovered at Gona in Ethiopia.[16] After this date, the Oldowan Industry subsequently spread throughout much of Africa, although archaeologists are currently unsure which Hominan species first developed them, with some speculating that it was Australopithecus garhi, and others believing that it was in fact Homo habilis.[17]

    Homo habilis was the hominin who used the tools for most of the Oldowan in Africa, but at about 1.9-1.8 million years ago Homo erectus inherited them. The Industry flourished in southern and eastern Africa between 2.6 and 1.7 million years ago, but was also spread out of Africa and into Eurasia by travelling bands of H. erectus, who took it as far east as Java by 1.8 million years ago and Northern China by 1.6 million years ago.
    |]
    "",

    CalendarEntry (1.8 & millionYearsAgo) Nothing
    "First major transition in stone tool technology"
    "Mode II: The Acheulean Industry"
    "From the Konso Formation of Ethiopia, Acheulean hand-axes are dated to about 1.5 million years ago using radiometric dating of deposits containing volcanic ashes.[6] Acheulean tools in South Asia have also been found to be dated as far as 1.5 million years ago.[7] However, the earliest accepted examples of the Acheulean currently known come from the West Turkana region of Kenya and were first described by a French-led archaeology team.[8] These particular Acheulean tools were recently dated through the method of magnetostratigraphy to about 1.76 million years ago, making them the oldest not only in Africa but the world.[9] The earliest user of Acheulean tools was Homo ergaster, who first appeared about 1.8 million years ago. Not all researchers use this formal name, and instead prefer to call these users early Homo erectus.[3]"
    "",

    CalendarEntry (160 & thousandYearsAgo) Nothing
    "Second major transition in stone tool technology"
    "Mode III: The Levallois technique; The Mousterian Industry"
    [text|
    (Stone scrapers, knives, and projectile points)

    The technique is first found in the Lower Palaeolithic but is most commonly associated with the Neanderthal Mousterian industries of the Middle Palaeolithic. In the Levant, the Levallois technique was also used by anatomically modern humans during the Middle Stone Age. In North Africa, the Levallois technique was used in the Middle Stone Age, most notably in the Aterian industry to produce very small projectile points. While Levallois cores do display some variability in their platforms, their flake production surfaces show remarkable uniformity. As the Levallois technique is counterintuitive, teaching the process is necessary and thus language is a prerequisite for such technology.[2]

    The Mousterian (or Mode III) is a techno-complex (archaeological industry) of stone tools, associated primarily with the Neanderthals in Europe, and to a lesser extent the earliest anatomically modern humans in North Africa and West Asia. The Mousterian largely defines the latter part of the Middle Paleolithic, the middle of the West Eurasian Old Stone Age. It lasted roughly from 160,000 to 40,000 BP. If its predecessor, known as Levallois or Levallois-Mousterian, is included, the range is extended to as early as c. 300,000–200,000 BP.[2] The main following period is the Aurignacian (c. 43,000–28,000 BP) of Homo sapiens.
    |]
    "",

    CalendarEntry (115 & thousandYearsAgo) (Just $ 11.7 & thousandYearsAgo)
    "The Ice Age begins"
    "The Last Glacial Period"
    "The Last Glacial Period (LGP), also known colloquially as the last ice age or simply ice age,[1] occurred from the end of the Eemian to the end of the Younger Dryas, encompassing the period c. 115,000 – c. 11,700 years ago. The LGP is part of a larger sequence of glacial and interglacial periods known as the Quaternary glaciation which started around 2,588,000 years ago and is ongoing.[2] The definition of the Quaternary as beginning 2.58 million years ago (Mya) is based on the formation of the Arctic ice cap. The Antarctic ice sheet began to form earlier, at about 34 Mya, in the mid-Cenozoic (Eocene–Oligocene extinction event). The term Late Cenozoic Ice Age is used to include this early phase.[3]"
    "https://en.wikipedia.org/wiki/Last_Glacial_Period",

    CalendarEntry (50 & thousandYearsAgo) Nothing
    "Third major transition in stone tool technology"
    "Mode IV: The Aurignacian Industry"
    "The widespread use of long blades (rather than flakes) of the Upper Palaeolithic Mode 4 industries appeared during the Upper Palaeolithic between 50,000 and 10,000 years ago, although blades were produced in small quantities much earlier by Neanderthals.[20] The Aurignacian culture seems to have been the first to rely largely on blades.[21] The use of blades exponentially increases the efficiency of core usage compared to the Levallois flake technique, which had a similar advantage over Acheulean technology which was worked from cores."
    "https://en.wikipedia.org/wiki/Stone_tool#Mode_IV:_The_Aurignacian_Industry",

    CalendarEntry (35 & thousandYearsAgo) Nothing
    "Last major transition in stone tool technology"
    "Mode V: The Microlithic Industries"
    "Mode 5 stone tools involve the production of microliths, which were used in composite tools, mainly fastened to a shaft.[22] Examples include the Magdalenian culture. Such a technology makes much more efficient use of available materials like flint, although required greater skill in manufacturing the small flakes. Mounting sharp flint edges in a wood or bone handle is the key innovation in microliths, essentially because the handle gives the user protection against the flint and also improves leverage of the device."
    "https://en.wikipedia.org/wiki/Stone_tool#Mode_V:_The_Microlithic_Industries"
    ,

    CalendarEntry (12 & thousandYearsAgo) Nothing
    "Agriculture leads to permanent settlements"
    "Neolithic age (\"new stone age\")"
    "Wild grains were collected and eaten from at least 105,000 years ago.[2] However, domestication did not occur until much later. The earliest evidence of small-scale cultivation of edible grasses is from around 21,000 BC with the Ohalo II people on the shores of the Sea of Galilee.[3] By around 9500 BC, the eight Neolithic founder crops – emmer wheat, einkorn wheat, hulled barley, peas, lentils, bitter vetch, chickpeas, and flax – were cultivated in the Levant.[4] Rye may have been cultivated earlier, but this claim remains controversial.[5] Rice was domesticated in China by 6200 BC[6] with earliest known cultivation from 5700 BC, followed by mung, soy and azuki beans. Rice was also independently domesticated in West Africa and cultivated by 1000 BC.[7][8] Pigs were domesticated in Mesopotamia around 11,000 years ago, followed by sheep. Cattle were domesticated from the wild aurochs in the areas of modern Turkey and India around 8500 BC. Camels were domesticated late, perhaps around 3000 BC."
    "https://en.wikipedia.org/wiki/History_of_agriculture",

    CalendarEntry (6.5 & thousandYearsAgo) Nothing
    "First copper tools"
    ""
    ""
    "",

    CalendarEntry (5.3 & thousandYearsAgo) Nothing
    "First bronze tools, first written language"
    "The Bronze Age"
    ""
    "",

    CalendarEntry (3000 & yearsBeforeCommonEra) (Just $ 2350 & yearsBeforeCommonEra)
    "Corded Ware culture"
    ""
    [text|
    The Corded Ware culture comprises a broad archaeological horizon of Europe between ca. 3000 BCE – 2350 BCE, thus from the late Neolithic, through the Copper Age, and ending in the early Bronze Age.[2] Corded Ware culture encompassed a vast area, from the contact zone between the Yamnaya culture and the Corded Ware culture in south Central Europe, to the Rhine on the west and the Volga in the east, occupying parts of Northern Europe, Central Europe and Eastern Europe.[2][3] The Corded Ware culture is thought to have originated from the westward migration of Yamnaya-related people from the steppe-forest zone into the territory of late Neolithic European cultures such as the Globular Amphora and Funnelbeaker cultures,[4][5][6] and is considered to be a likely vector for the spread of many of the Indo-European languages in Europe and Asia.[1][7][8][9]

    Corded Ware encompassed most of continental northern Europe from the Rhine on the west to the Volga in the east, including most of modern-day Germany, the Netherlands, Denmark, Poland, Lithuania, Latvia, Estonia, Belarus, Czech Republic, Austria, Hungary, Slovakia, Switzerland, northwestern Romania, northern Ukraine, and the European part of Russia, as well as coastal Norway and the southern portions of Sweden and Finland.[2] In the Late Eneolithic/Early Bronze Age, it encompassed the territory of nearly the entire Balkan Peninsula, where Corded Ware mixed with other steppe elements.[11]

    Archaeologists note that Corded Ware was not a "unified culture," as Corded Ware groups inhabiting a vast geographical area from the Rhine to Volga seem to have regionally specific subsistence strategies and economies.[2]: 226  There are differences in the material culture and in settlements and society.[2] At the same time, they had several shared elements that are characteristic of all Corded Ware groups, such as their burial practices, pottery with "cord" decoration and unique stone-axes.[2]
    |]
    "",

    CalendarEntry (2800 & yearsBeforeCommonEra) (Just $ 1800 & yearsBeforeCommonEra)
    "Bell Beaker culture"
    ""
    [text|
    The Bell Beaker culture (also described as the Bell Beaker complex or Bell Beaker phenomenon) is an archaeological culture named after the inverted-bell beaker drinking vessel used at the very beginning of the European Bronze Age. Arising from around 2800 BC, it lasted in Britain until as late as 1800 BC[1][2] but in continental Europe only until 2300 BC, when it was succeeded by the Unetice culture. The culture was widely dispersed throughout Western Europe, being present in many regions of Iberia and stretching eastward to the Danubian plains, and northward to the islands of Great Britain and Ireland, and was also present in the islands of Sicily and Sardinia and some small coastal areas in north-western Africa. The Bell Beaker phenomenon shows substantial regional variation, and a study[3] from 2018 found that it was associated with genetically diverse populations.

    In its mature phase, the Bell Beaker culture is understood as not only a collection of characteristic artefact types, but a complex cultural phenomenon involving metalwork in copper and gold, long-distance exchange networks, archery, specific types of ornamentation, and (presumably) shared ideological, cultural and religious ideas, as well as social stratification and the emergence of regional elites.[6][7] A wide range of regional diversity persists within the widespread late Beaker culture, particularly in local burial styles (including incidences of cremation rather than burial), housing styles, economic profile, and local ceramic wares (Begleitkeramik). Nonetheless, according to Lemercier (2018) the mature phase of the Beaker culture represents "the appearance of a kind of Bell Beaker civilization of continental scale."[8]

    Bell Beaker people took advantage of transport by sea and rivers, creating a cultural spread extending from Ireland to the Carpathian Basin and south along the Atlantic coast and along the Rhône valley to Portugal, North Africa, and Sicily, even penetrating northern and central Italy.[50] Its remains have been found in what is now Portugal, Spain, France (excluding the central massif), Ireland and Great Britain, the Low Countries and Germany between the Elbe and Rhine, with an extension along the upper Danube into the Vienna Basin (Austria), Hungary and the Czech Republic, with Mediterranean outposts on Sardinia and Sicily; there is less certain evidence for direct penetration in the east.
    |]
    "https://en.wikipedia.org/wiki/Bell_Beaker_culture",

    CalendarEntry (11.7 & thousandYearsAgo) Nothing
    "Ice Age ends"
    ""
    ""
    "https://en.wikipedia.org/wiki/Last_Glacial_Period",

    CalendarEntry (1600 & yearsBeforeCommonEra) Nothing
    "Dynastic China"
    "History begins"
    [text|
    The earliest known written records of the history of China date from as early as 1250 BC, from the Shang dynasty (c. 1600–1046 BC), during the king Wu Ding's reign

    The state-sponsored Xia–Shang–Zhou Chronology Project dated them from c. 1600 to 1046 BC based on the carbon 14 dates of the Erligang site.
    |]
    "",

    CalendarEntry (theYear 1492) Nothing
    "Columbus arrives in America"
    ""
    ""
    "",

    CalendarEntry (theYear 570) Nothing
    "Muhammad born"
    ""
    ""
    "",

    CalendarEntry (480 & yearsBeforeCommonEra) Nothing
    "Old Testament, Buddha"
    ""
    ""
    "",

    CalendarEntry (8.8 & billionYearsAgo) Nothing
    "Thin disk of the Milky Way Galaxy"
    "Our galaxy begins to form"
    "The age of stars in the galactic thin disk has also been estimated using nucleocosmochronology. Measurements of thin disk stars yield an estimate that the thin disk formed 8.8 ± 1.7 billion years ago. These measurements suggest there was a hiatus of almost 5 billion years between the formation of the galactic halo and the thin disk.[253] Recent analysis of the chemical signatures of thousands of stars suggests that stellar formation might have dropped by an order of magnitude at the time of disk formation, 10 to 8 billion years ago, when interstellar gas was too hot to form new stars at the same rate as before.[254] "
    "",

    CalendarEntry (3.4 & billionYearsAgo) Nothing
    "First photosynthetic bacteria"
    "(Still no Oxygen)"
    "They absorbed near-infrared rather than visible light and produced sulfur or sulfate compounds rather than oxygen. Their pigments (possibly bacteriochlorophylls) were predecessors to chlorophyll."
    "https://www.scientificamerican.com/article/timeline-of-photosynthesis-on-earth/",

    CalendarEntry (2.7 & billionYearsAgo) Nothing
    "Oxygen from photosynthesis"
    "Cyanobacteria"
    "These ubiquitous bacteria were the first oxygen producers. They absorb visible light using a mix of pigments: phycobilins, carotenoids and several forms of chlorophyll."
    "https://www.scientificamerican.com/article/timeline-of-photosynthesis-on-earth/",

    CalendarEntry (1.2 & billionYearsAgo) Nothing
    "Red and brown algae"
    ""
    "These organisms have more complex cellular structures than bacteria do. Like cyanobacteria, they contain phycobilin pigments as well as various forms of chlorophyll."
    "https://www.scientificamerican.com/article/timeline-of-photosynthesis-on-earth/",

    CalendarEntry (0.75 & billionYearsAgo) Nothing
    "Green algae"
    ""
    "Green algae do better than red and brown algae in the strong light of shallow water. They make do without phycobilins."
    "https://www.scientificamerican.com/article/timeline-of-photosynthesis-on-earth/",

    CalendarEntry (0.475 & billionYearsAgo) Nothing
    "First land plants"
    ""
    "Mosses and liverworts descended from green algae. Lacking vascular structure (stems and roots) to pull water from the soil, they are unable to grow tall."
    "https://www.scientificamerican.com/article/timeline-of-photosynthesis-on-earth/",

    CalendarEntry (0.423 & billionYearsAgo) Nothing
    "Vascular plants"
    ""
    "These are literally garden-variety plants, such as ferns, grasses, trees and cacti. They are able to grow tall canopies to capture more light."
    "https://www.scientificamerican.com/article/timeline-of-photosynthesis-on-earth/",

    CalendarEntry (2.05 & billionYearsAgo) Nothing
    "Eukaryotic cells"
    "Cells with nucleus (inner membrane holding DNA)"
    [text|
    Eukaryotes (/juːˈkærioʊts, -əts/) are organisms whose cells have a nucleus enclosed within a nuclear envelope.[1][2][3] They belong to the group of organisms Eukaryota or Eukarya; their name comes from the Greek εὖ (eu, "well" or "good") and κάρυον (karyon, "nut" or "kernel").[4] The domain Eukaryota makes up one of the three domains of life; bacteria and archaea (both prokaryotes) make up the other two domains.[5][6] The eukaryotes are usually now regarded as having emerged in the Archaea or as a sister of the Asgard archaea.[7][8] This implies that there are only two domains of life, Bacteria and Archaea, with eukaryotes incorporated among archaea.[9][10] Eukaryotes represent a small minority of the number of organisms;[11] however, due to their generally much larger size, their collective global biomass is estimated to be about equal to that of prokaryotes.[11] Eukaryotes emerged approximately 2.3–1.8 billion years ago, during the Proterozoic eon, likely as flagellated phagotrophs.[12][13]
    |]
    "https://en.wikipedia.org/wiki/Eukaryote",

    CalendarEntry (3.77 & billionYearsAgo) Nothing
    "Life on Earth"
    ""
    [text|
    The earliest time for the origin of life on Earth is at least 3.77 billion years ago, possibly as early as 4.28 billion years,[2] or even 4.41 billion years[4][5]—not long after the oceans formed 4.5 billion years ago, and after the formation of the Earth 4.54 billion years ago.[2][3][6][7]
    |]
    "https://en.wikipedia.org/wiki/Earliest_known_life_forms",

    CalendarEntry (3.42 & billionYearsAgo) Nothing
    "Earliest known life on Earth"
    ""
    [text|
    The earliest known life forms on Earth are putative fossilized microorganisms found in hydrothermal vent precipitates, considered to be about 3.42 billion years old.[1][2] The earliest time for the origin of life on Earth is at least 3.77 billion years ago, possibly as early as 4.28 billion years,[2] or even 4.41 billion years[4][5]—not long after the oceans formed 4.5 billion years ago, and after the formation of the Earth 4.54 billion years ago.[2][3][6][7] The earliest direct evidence of life on Earth is from microfossils of microorganisms permineralized in 3.465-billion-year-old Australian Apex chert rocks.[8][9] 
    |]
    "https://en.wikipedia.org/wiki/Earliest_known_life_forms",

    CalendarEntry (750 & millionYearsAgo) Nothing
    "Bones and shells"
    ""
    [text|
    A series of spectacularly preserved, 750-million-year-old fossils represent the microscopic origins of biomineralization, or the ability to convert minerals into hard, physical structures. This process is what makes bones, shells, teeth and hair possible, literally shaping the animal kingdom and even Earth itself.

    The fossils were pried from ancient rock formations in Canada's Yukon by earth scientists Francis Macdonald and Phoebe Cohen of Harvard University. In a June Geology paper, they describe their findings as providing "a unique window into the diversity of early eukaryotes."

    Using molecular clocks and genetic trees to reverse-engineer evolutionary histories, previous research placed the beginning of biomineralization at about 750 million years ago. Around that time, the fossil record gets suggestive, turning up vase-shaped amoebas with something like scales in their cell walls, algae with cell walls possibly made from calcium carbonate and sponge-like creatures with seemingly mineralized bodies.
    |]
    "https://www.wired.com/2011/06/first-shells/",

    CalendarEntry (440 & millionYearsAgo) Nothing
    "Fish with jaws"
    ""
    [text|
    Prehistoric armoured fishes called placoderms were the first fishes to have jaws. They arose some time in the Silurian Period, about 440 million years ago, to become the most abundant and diverse fishes of their day.

Placoderms dominated the oceans, rivers and lakes for some 80 million years, before their sudden extinction around 359 million years ago. This is possibly due to the depletion of trace elements in our oceans.
    |]
    "",

    CalendarEntry (518 & millionYearsAgo) Nothing
    "Vertebrates"
    "Animals with backbones"
    [text|
    Vertebrates (/ˈvɜːrtəbrɪts, -ˌbreɪts/)[3] comprise all animal taxa within the subphylum Vertebrata (/ˌvɜːrtəˈbreɪtə/)[4] (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described.[5]
    |]
    "",

    CalendarEntry (385 & millionYearsAgo) Nothing
    "Insects"
    ""
    [text|
    Comprising up to 10 million living species, insects today can be found on all seven continents and inhabit every terrestrial niche imaginable. But according to the fossil record, they were scarce before about 325 million years ago, outnumbered by their arthropod cousins the arachnids (spiders, scorpions and mites) and myriapods (centipedes and millipedes).

    The oldest confirmed insect fossil is that of a wingless, silverfish-like creature that lived about 385 million years ago. It’s not until about 60 million years later, during a period of the Earth’s history known as the Pennsylvanian, that insect fossils become abundant.
    |]
    "https://earth.stanford.edu/news/insects-took-when-they-evolved-wings",

    CalendarEntry (368 & millionYearsAgo) Nothing
    "Amphibians"
    ""
    [text|
    The earliest well-known amphibian, Ichthyostega, was found in Late Devonian deposits in Greenland, dating back about 363 million years. The earliest amphibian discovered to date is Elginerpeton, found in Late Devonian rocks of Scotland dating to approximately 368 million years ago. The later Paleozoic saw a great diversity of amphibians, ranging from small legless swimming forms (Aistopoda) to bizarre "horned" forms (Nectridea). Other Paleozoic amphibians more or less resembled salamanders outwardly but differed in details of skeletal structure. Exactly how to classify these fossils, and how they might be related to living amphibians, is still debated by paleontologists. Shown at the right is Phlegethontia, an aistopod from the Pennsylvanian.

     The familiar frogs, toads, and salamanders have been present since at least the Jurassic Period. (The fossil frog pictured to the left is much younger, coming from the Eocene, only 45 to 55 million years ago). Fossil caecilians are very rare; until recently the oldest known caecilians were Cenozoic in age (that is, less than 65 million years old), but recent finds have pushed back the ancestry of the legless caecilians to Jurassic ancestors that had short legs. The rarity of fossil caecilians is probably due to their burrowing habitat and reduced skeleton, both of which lessen the chances of preservation.

    |]
    "https://ucmp.berkeley.edu/vertebrates/tetrapods/amphibfr.html",

    CalendarEntry (320 & millionYearsAgo) Nothing
    "Reptiles"
    ""
    [text|
    Reptiles, in the traditional sense of the term, are defined as animals that have scales or scutes, lay land-based hard-shelled eggs, and possess ectothermic metabolisms.

    Though few reptiles today are apex predators, many examples of apex reptiles have existed in the past. Reptiles have an extremely diverse evolutionary history that has led to biological successes, such as dinosaurs, pterosaurs, plesiosaurs, mosasaurs, and ichthyosaurs.
    |]
    [text|
    https://en.wikipedia.org/wiki/Evolution_of_reptiles
    https://www.thoughtco.com/the-first-reptiles-1093767
    |],

    CalendarEntry (335 & millionYearsAgo) Nothing
    "Pangea forms"
    ""
    [text|
    Pangaea or Pangea (/pænˈdʒiː.ə/)[1] was a supercontinent that existed during the late Paleozoic and early Mesozoic eras.[2] It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million years ago, and began to break apart about 200 million years ago, at the end of the Triassic and beginning of the Jurassic.[3] In contrast to the present Earth and its distribution of continental mass, Pangaea was centred on the Equator and surrounded by the superocean Panthalassa and the Paleo-Tethys and subsequent Tethys Oceans. Pangaea is the most recent supercontinent to have existed and the first to be reconstructed by geologists.
    |]
    "https://en.wikipedia.org/wiki/Pangaea",

    CalendarEntry (243 & millionYearsAgo) Nothing
    "Dinosaurs"
    ""
    [text|
    For the past twenty years, Eoraptor has represented the beginning of the Age of Dinosaurs. This controversial little creature–found in the roughly 231-million-year-old rock of Argentina–has often been cited as the earliest known dinosaur. But Eoraptor has either just been stripped of that title, or soon will be. A newly-described fossil found decades ago in Tanzania extends the dawn of the dinosaurs more than 10 million years further back in time.

Named Nyasasaurus parringtoni, the roughly 243-million-year-old fossils represent either the oldest known dinosaur or the closest known relative to the earliest dinosaurs. The find was announced by University of Washington paleontologist Sterling Nesbitt and colleagues in Biology Letters, and I wrote a short news item about the discovery for Nature News. The paper presents a significant find that is also a tribute to the work of Alan Charig–who studied and named the animal, but never formally published a description–but it isn’t just that. The recognition of Nyasasaurus right near the base of the dinosaur family tree adds to a growing body of evidence that the ancestors of dinosaurs proliferated in the wake of a catastrophic mass extinction.
    |]
    [text|
    https://www.smithsonianmag.com/science-nature/scientists-discover-oldest-known-dinosaur-152807497/
    |],

    CalendarEntry (210 & millionYearsAgo) Nothing
    "Mammals"
    ""
    [text|
    The earliest known mammals were the morganucodontids, tiny shrew-size creatures that lived in the shadows of the dinosaurs 210 million years ago. They were one of several different mammal lineages that emerged around that time. All living mammals today, including us, descend from the one line that survived.
    |]
    "https://www.nationalgeographic.com/science/article/rise-mammals",

    CalendarEntry (150 & millionYearsAgo) Nothing
    "Birds"
    ""
    [text|
    The first birds had sharp teeth, long bony tails and claws on their hands. The clear distinction we see between living birds and other animals did not exist with early birds. The first birds were in fact more like small dinosaurs than they were like any bird today.

    The earliest known (from fossils) bird is the 150-million-year-old Archaeopteryx, but birds had evolved before then. A range of birds with more advanced features appeared soon after Archaeopteryx. One group gave rise to modern birds in the Late Cretaceous.
    |]
    "https://australian.museum/learn/dinosaurs/the-first-birds/",

    CalendarEntry (130 & millionYearsAgo) Nothing
    "Flowers"
    ""
    [text|
    Today, plants with flowers--called angiosperms--dominate the landscape. Around 80 percent of green plants alive today, from oak trees to grass, are flowering plants. In all of these plants, flowers are part of the reproductive system. But 130 million years ago, flowering plants were rare. Most plants reproduced with spores, found today on ferns, or with seeds and cones, found today on pine trees. The plant fossils found in Liaoning, China, show evidence of plants with spores or seeds--and perhaps one of the first flowering plants.

    Researchers have found an ancient plant in Liaoning, Archaefructus, that has very small, simple flowers and could be one of the first flowering plants. Archaefructus lived around 130 million years ago and probably grew in or near the water.
    |]
    "https://www.amnh.org/exhibitions/dinosaurs-ancient-fossils/liaoning-diorama/when-flowers-first-bloomed",

    CalendarEntry (85 & millionYearsAgo) Nothing
    "Tyranosaurids"
    "The Tyrant Lizards"
    [text|
    The name says it all. This group of huge carnivores must have tyrannically ruled the land during the last part of the Cretaceous, 85 to 65 million years ago. Short but deep jaws with banana-sized sharp teeth, long hind limbs, small beady eyes, and tiny forelimbs (arms) typify a tyrannosaur. The Tyrannosauridae included such similar animals (in rough order of increasing size) as Albertosaurus, Gorgosaurus, Daspletosaurus, Tarbosaurus, and of course Tyrannosaurus rex.

    T. rex was one of the largest terrestrial carnivores of all time. It stood approximately 15 feet high and was about 40 feet in length, roughly six tons in weight. In its large mouth were six-inch long, sharp, serrated teeth.

    Just about two dozen good specimens of these animals have been found and these finds are from highly restricted areas in western North America. Henry Fairfield Osborn, of the American Museum of Natural History in New York City, first described Tyrannosaurus rex in 1905. This first specimen of Tyrannosaurus is now on display at the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania.
    |]
    "",

    CalendarEntry (65 & millionYearsAgo) Nothing
    "Dinosaurs extinct"
    "Mammals take over land & sea"
    [text|
    |]
    "",

    CalendarEntry (27.5 & millionYearsAgo) Nothing
    "Apes and monkeys split"
    ""
    [text|
    Studies of clock-like mutations in primate DNA have indicated that the split between apes and Old World monkeys occurred between 30 million and 25 million years ago.
    |]
    "https://www.nsf.gov/news/news_summ.jsp?cntn_id=127930",

    CalendarEntry (12.1 & millionYearsAgo) Nothing
    "Humans and chimpanzees split"
    ""
    [text|
    A 2016 study analyzed transitions at CpG sites in genome sequences, which exhibit a more clocklike behavior than other substitutions, arriving at an estimate for human and chimpanzee divergence time of 12.1 million years.[20]
    |]
    [text|
    https://en.wikipedia.org/wiki/Chimpanzee%E2%80%93human_last_common_ancestor
    |],

    CalendarEntry (4.4 & millionYearsAgo) Nothing
    "Humans first walk upright"
    ""
    [text|
    The earliest hominid with the most extensive evidence for bipedalism is the 4.4-million-year-old Ardipithecus ramidus.
    |]
    [text|
    https://www.smithsonianmag.com/science-nature/becoming-human-the-evolution-of-walking-upright-13837658/
    |],

    CalendarEntry (300 & thousandYearsAgo) Nothing
    "Modern humans evolve"
    ""
    [text|
    Among the oldest known remains of Homo sapiens are those found at the Omo-Kibish I archaeological site in south-western Ethiopia, dating to about 233,000[2] to 196,000 years ago,[3] the Florisbad site in South Africa, dating to about 259,000 years ago, and the Jebel Irhoud site in Morocco, dated about 300,000 years ago.
    |]
    [text|
    https://en.wikipedia.org/wiki/Early_modern_human
    |],

    CalendarEntry (100 & thousandYearsAgo) Nothing
    "Human migration out of Africa"
    ""
    [text|
    Between 70,000 and 100,000 years ago, Homo sapiens began migrating from the African continent and populating parts of Europe and Asia. They reached the Australian continent in canoes sometime between 35,000 and 65,000 years ago.

    Map of the world showing the spread of Homo sapiens throughout the Earth over time.
    |]
    [text|
    https://www.khanacademy.org/humanities/world-history/world-history-beginnings/origin-humans-early-societies/a/where-did-humans-come-from
    |],

    CalendarEntry (4.4 & billionYearsAgo) Nothing
    "Formation of the moon"
    "A collision of the planet Theia with Earth creates the moon"
    [text|
    Astronomers think the collision between Earth and Theia happened at about 4.4 to 4.45 bya; about 0.1 billion years after the Solar System began to form.[15][16] In astronomical terms, the impact would have been of moderate velocity. Theia is thought to have struck Earth at an oblique angle when Earth was nearly fully formed. Computer simulations of this "late-impact" scenario suggest an initial impactor velocity at infinity below 4 kilometres per second (2.5 mi/s), increasing as it fell to over 9.3 km/s (5.8 mi/s) at impact, and an impact angle of about 45°.[17] However, oxygen isotope abundance in lunar rock suggests "vigorous mixing" of Theia and Earth, indicating a steep impact angle.[3][18] Theia's iron core would have sunk into the young Earth's core, and most of Theia's mantle accreted onto Earth's mantle. However, a significant portion of the mantle material from both Theia and Earth would have been ejected into orbit around Earth (if ejected with velocities between orbital velocity and escape velocity) or into individual orbits around the Sun (if ejected at higher velocities). Modelling[19] has hypothesised that material in orbit around Earth may have accreted to form the Moon in three consecutive phases; accreting first from the bodies initially present outside Earth's Roche limit, which acted to confine the inner disk material within the Roche limit. The inner disk slowly and viscously spread back out to Earth's Roche limit, pushing along outer bodies via resonant interactions. After several tens of years, the disk spread beyond the Roche limit, and started producing new objects that continued the growth of the Moon, until the inner disk was depleted in mass after several hundreds of years.
    |]
    [text|
    https://en.wikipedia.org/wiki/Giant-impact_hypothesis#Basic_model
    https://www.psi.edu/epo/moon/moon.html
    |],

    CalendarEntry (600 & millionYearsAgo) Nothing
    "Multicellular life"
    ""
    [text|
    |]
    ""
    ]

  where
    theYear = yearsAgo . toRational . (currentYear -)
    yearsBeforeCommonEra = yearsAgo . toRational . ((+) (currentYear - 1))
    earthDescription = [text|
      The standard model for the formation of the Solar System (including the Earth) is the solar nebula hypothesis.[23] In this model, the Solar System formed from a large, rotating cloud of interstellar dust and gas called the solar nebula. It was composed of hydrogen and helium created shortly after the Big Bang 13.8 Ga (billion years ago) and heavier elements ejected by supernovae. About 4.5 Ga, the nebula began a contraction that may have been triggered by the shock wave from a nearby supernova.[24] A shock wave would have also made the nebula rotate. As the cloud began to accelerate, its angular momentum, gravity, and inertia flattened it into a protoplanetary disk perpendicular to its axis of rotation. Small perturbations due to collisions and the angular momentum of other large debris created the means by which kilometer-sized protoplanets began to form, orbiting the nebular center.[25]

      The center of the nebula, not having much angular momentum, collapsed rapidly, the compression heating it until nuclear fusion of hydrogen into helium began. After more contraction, a T Tauri star ignited and evolved into the Sun. Meanwhile, in the outer part of the nebula gravity caused matter to condense around density perturbations and dust particles, and the rest of the protoplanetary disk began separating into rings. In a process known as runaway accretion, successively larger fragments of dust and debris clumped together to form planets.[25] Earth formed in this manner about 4.54 billion years ago (with an uncertainty of 1%)[26][27][4] and was largely completed within 10–20 million years.[28] The solar wind of the newly formed T Tauri star cleared out most of the material in the disk that had not already condensed into larger bodies. The same process is expected to produce accretion disks around virtually all newly forming stars in the universe, some of which yield planets.[29]
    |]
    recombinationDescription = [text|
      At about 370,000 years,[3][4][5][6] neutral hydrogen atoms finish forming ("recombination"), and as a result the universe also became transparent for the first time. The newly formed atoms—mainly hydrogen and helium with traces of lithium—quickly reach their lowest energy state (ground state) by releasing photons ("photon decoupling"), and these photons can still be detected today as the cosmic microwave background (CMB). This is the oldest direct observation we currently have of the universe.
    |]
    recombinationReferences = [text|
      https://en.wikipedia.org/wiki/Chronology_of_the_universe#The_very_early_universe

      3. Tanabashi, M. 2018, p. 358, chpt. 21.4.1: "Big-Bang Cosmology" (Revised
      September 2017) by Keith A. Olive and John A. Peacock.

      4. Notes: Edward L. Wright's Javascript Cosmology Calculator (last
      modified 23 July 2018). With a default H 0 {\displaystyle H_{0}} H_{0} =
      69.6 (based on WMAP9+SPT+ACT+6dFGS+BOSS/DR11+H0/Riess) parameters, the
      calculated age of the universe with a redshift of z = 1100 is in agreement
      with Olive and Peacock (about 370,000 years).

      5. Hinshaw, Weiland & Hill 2009. See PDF: page 45, Table 7, Age at
      decoupling, last column. Based on WMAP+BAO+SN parameters, the age of
      decoupling occurred 376971+3162−3167 years after the Big Bang.

      6. Ryden 2006, pp. 194–195. "Without going into the details of the
      non-equilibrium physics, let's content ourselves by saying, in round
      numbers, zdec ≈ 1100, corresponding to a temperature Tdec ≈ 3000 K, when
      the age of the universe was tdec ≈ 350,000 yr in the Benchmark Model.
      (...) The relevant times of various events around the time of
      recombination are shown in Table 9.1. (...) Note that all these times are
      approximate, and are dependent on the cosmological model you choose. (I
      have chosen the Benchmark Model in calculating these numbers.)"

      https://en.wikipedia.org/wiki/Recombination_(cosmology)#cite_note-2

    |]