A few fragments of prehistory

When I read about something happening 150 million years ago, I can't remember how that relates to what other things how long ago; so I'll collect together here the fragments that shall, in due course, accumulate to a time-line. For more extensive topic-specific time-lines, consult Wikipedia. For sources (in so far as I'm able to trace them), follow links.

In the spirit of my page on the scale of things, I'll break this up into chunks by metric quantifier on number of years before the present (nominally 2000; and I habitually use whatever quantifier puts the number in the range from about 0.1 to about 100) in the main list. (For events whose timing is known most accurately relative to The Big Bang, I include a separate tail-piece, presently with too few entries to warrand such splitting.) Only three quantifies show up, though: the k yr range tells the tale of humanity's development; the M yr range is the era of fossils; and the G yr range is the time-scale of cosmology. Shorter time-scales I classify as history on a page of their own; and time itself is only meaningful back to the start of the universe, so no longer time-scale is relevant here.

k yr, a.k.a. millennium

A century ago radio was a novel concept and not much in use. Recorded history stretches back of order ten millennia, to roughly the point where the present ice age (which stretches back at least about a hundred millennia) entered its present interglacial phase (in which only the North polar sea and the South polar continent are ice-locked). The duration of such inter-glacial interludes is generally of order ten millennia. We have archeological records stretching back significantly further than those ten millennia, though.

10ish to 5ish k yr ago
The development of writing and, as a result, history. From this point on, written records give us far more detailed information about events – and the archeological record is vastly more detailed, too – so we know more about the last few millennia than about everything that came before. As a result, I separate out the last ten millennia into their own page on history.
11.5 to 8 k yr ago

The Neolithic era, a.k.a. new stone age. People began living in relatively permanent villages and domesticating crops and (other) animals. Archeologists have found buildings from as much as 11 k yr ago.

9.4 to 7.7 k yr ago

Çatalhöyük (Çatal = fork (in a path), höyük = mound), in Anatolia, was inhabited, moving from the large mound to the small mound around 8 k yr ago, with a population fluctuating from 3 to 8 k.

9.5 k yr ago

Oldest archeological evidence of cats and humans cohabiting. For more solid evidence of domestication, one has to wait another 4.2 k yr.

12 to 11 k yr ago

Evidence of early neolithic agriculture: a variety of fig prospering, that normally wouldn't survive, as it needs human intervention to propagate it from cuttings.

Around the same time, the Natufian culture is known to have domesticated dogs in the middle East (mentioned here).

12 k yr ago

First successful human settlements in the British Isles.

10ish k yr ago onwards: the Holocene era
12.9 k yr ago
Comet impact maybe provoked climate change and disrupted ecologies in the northern hemisphere.
5 to 15 k yr ago

If we look at the set of ancestors of each human alive today, as a function of time, going backwards, there must come a point at which these sets are all identical, known as the identical ancestors point; this is estimated to be between five and fifteen millennia ago.

at least 14 k yr ago
The invention of pottery appears to have happened in East Asia – and took something like six thousand years to spread West to the Middle East and, thence, Africa and Europe.
15 k yr ago
Rice cultivation in East Asia (mentioned here, from Korean research).
10 to 18 k yr ago
The Magdalenian culture, ranging at least from the Iberian peninsula to what is now Poland, made tents and hunted large animals including reindeer; they made tools of flint, bone and antlers. Their resettlement of Europe came just as the ice age was taking a break for the present interglacial.
35 to 24 k yr ago
The end of the Neanderthals
40 to 10 k yr ago: upper Paleolithic

The first European humans were already painting erotic pictures 40 k yr ago.

39 k yr ago
Heinrich event 4, a 2 k yr period of sluggish circulation and falling temperatures in the Atlantic, associated with a desert period in Iberia at the end of the Neanderthals' era.
40 k yr ago
The invention of tallies, physical objects on which to make marks representing numbers – of cattle, slaves and trade-goods, for example. This long pre-dates (other kinds of) writing.
45 to 42 k yr ago

Modern humans in Russia.

c. 50 k yr ago

Modern humans in Australia.

c. 60 k yr ago

Estimated date of the patrilineal most recent common ancestor of all currently living humans, a.k.a. the Y-chromosomal Adam, based on study of the Y chromosomes of men from around the world.

70 to 75 k yr ago

Supervolcano on Sumatra explodes (creating lake Toba), possibly forcing the human gene-pool through a bottleneck, down to between one and ten thousand breeding pairs.

M yr

A third of a million years is about the same fraction of the Sun's life expectancy (tenish giga years) as the fraction a day is of a life-span of 80ish years.

You run and you run to catch up with The Sun – but it's sinking,
rushing around to come up behind you again.

The Sun is the same, in a relative way, but you're older;
shorter of breath and one day closer to death.

Pink Floyd

0.13 M yr ago

Ancestors of modern domestic cats diverge from those of their surviving wild relatives; they may have been living with humans all that time.

0.14 M yr ago

estimated date of the matrilineal most recent common ancestor of all humans, a.k.a. the Mitochondrial Eve, inferred from study of diversity in human mitochondrial DNA.

0.16 M yr ago

Fossils of modern humans (H.Sap.) in East Africa's Rift Valley have been dated to 0.16 M yr ago; our species is believed to have arisen 0.2 M yr ago in sub-saharan Africa, and to have migrated out of Africa – in small groups as early as 90 k yr ago and in significantly larger numbers from around 50 k yr ago.

0.4 to 0.2 M yr ago

Separation of Britain from mainland Europe. The North Sea was previously land-locked, but broke out through what is now The Channel, possibly in a single day, gouging a deep trench valley in the process.

0.7 to 0.5 M yr ago

Earliest human (or hominid ?) attempts at colonising the British Isles.

6.3 to 5 M yr ago

Last common ancestors of chimps and humans.

11 M yr ago

Emergence of felines as a separate group of carnivores. Some migrated to the Americas about 8 M yr ago, via the Berring land bridge.

41 to 34 M yr ago

Antarctica and South America separated, allowing an ocean current to circulate round Antarctica, via the Drake Passage, with major impact on Earth's climate – including Antarctica's glaciation.

40 M yr ago

Early primates with a mutation began to see red – the origin of colour vision.

48 M yr ago

Earliest evidence of zombie ants, whose behaviour is hijacked by a fungal infection.

65 M yr ago

Meteor strike in Yucatan, leaving the Chicxulub crater; dinosaurs died out in the aftermath.

G yrLife's increasing complexity: starting c. 3.9 G yr ago, bacteria c. 3.5 G
yr ago, photosynthesis 2.5 G yr ago, eucaryotes 1.5 G yr ago and the Cambrian
explosion 0.5 G yr ago

The universe appears to be about 13.7 G yr old; our solar system formed four to five G yr ago and the third major planet (our home, Earth) from its star (The Sun) has teemed with life for much of the time since, acquiring its oxygen-rich atmosphere around 2 G yr ago. The Sun is expected to survive for about another four or five G yr.

0.1 G yr ago

Australia split off from Gondwanaland, after a slow splitting-up along a rift valley. The oldest known amber-fossil of a bee dates from about the same time.

0.168 to 0.14 G yr ago: Origin of the ants

A lesson for us all subsequently diversifying around 100 M yr ago, in concert with the flowering plants.

0.251 G yr ago

The Permian-Triassic mass-extinction, possibly caused by a meteor strike; the resulting crater, lurking under Antarctic ice, is about 480 km (300 miles) wide. This is also roughly when Gondwanaland (Pangea ?) began breaking up, possibly also thanks to that meteor. Life barely survived, some of it sheltering in coastal waters.

0.29 to 0.248 G yr ago
The Permian era, during which the world's land-masses were all fused together as Pangea, stretching from pole to pole. Ferns begin being displaced by seed-bearing plants; and conifers emerge.
0.4 to 0.45 G yr ago
Evolutionary divergence of the arachnids (spiders, scorpions, mites and ticks).
0.45 G yr ago

A mass-extinction wiped out plenty of life on Earth.

0.85 to 0.544 G yr ago

The Cryogenian era, including 0.2 G yr of the Neoproterozoic era. The period is known to have seen extensive glaciation, reaching even to the tropics, but (at least) the era is believed to have seen interglacial warmings.

0.8 G yr ago

Odd changes happened to ocean chemistry, possibly caused by a true polar wander incident – the Earth realigning itself around its spin axis in the space of a few million years.

2.7 to 2.3 G yr ago: Oxygen atmosphere

cyanobacteria (a.k.a. blue-green algae) showed up somewhat earlier, but at this point their environmental pollution became a major part of the atmosphere. It might be arguable that the damage took a few more mega years to entrench itself.

3.4 G yr ago: Early life

Stomatolites in Pilbara, Western Australia, are 3.4 G yr old and some experts maintain that their origin is biological.

3.9 to 3.75 G yr ago: Oldest rocks

Rocks as old as 3.75 G yr can be found in the Hudson Bay area of Canada and in West Greenland. The Hudson Bay rocks reveal high levels of CO2 in the atmosphere at a time when the Sun is believed to have been about 25% less bright than it is today; without the CO2, oceans would have frozen. Rocks allegedly formed earlier, as much as 3.9 G yr ago.

4.3 G yr ago
Earth (possibly) cool enough to have liquid water.
4.6 or 4.5 G yr ago

Formation of Earth and Moon. Meanwhile, a collision in the Kuiper built broke up 2003 EL61 (which might otherwise have been bigger than Pluto).

4.56 G yr ago: Iapetus formed
Saturn's moon Iapetus has a ridge round its equator; one theory to explain this involves it forming quite early in the Solar System's history.
13.7 G yr ago: The Big Bang

Close study of the cosmic microwave background reveals that the universe is 13.7 gigayears old. The first few gigayears were dominated by an initial explosion and the progression of phases through which the results expanded and cooled; so I describe them below in terms of time after that initial explosion.

The first Gigayear

0.38 or 0.37 M yr: matter and light decouple

Energy densities got low enough that matter was no longer being excited back into unstable states as fast as it could decay out of them, so matter condensed out and formed atoms, leaving light to travel on its way, uninterrupted by absorption and only sporadically scattered. The resulting sea of photons, initially in thermal equilibrium with the matter, has been expanding and adiabatically cooling ever since. Today, it is observable as a background so far red-shifted that it is microwave radiation. It still retains the form of black body (i.e. thermal) radiation: indeed, it is the most perfect match yet seen to the theoretical model of such radiation.

five minutes
Atomic nuclei begin to freeze out from the nuclear plasma.
1 second
Exotic matter has almost all decayed into garden variety matter.
10 µs
Phase transition from quark-gluon liquid to hadron-lepton plasma.

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