Image from Steve Bowers

13.7 GYA (GigaYears Ago) (BIG BANG - FORMATION OF THE KNOWN PHYSICAL UNIVERSE)

13.7 TO 4.6 GYA: PRETERRAN EON

4.6 GYA: TERRAN HADEAN EON

3.8 GYA: TERRAN ARCHAEAN EON

2.5 GYA: TERRAN PROTEROZOIC EON

542 MYA: TERRAN PALEOZOIC ERA

251 MYA: TERRAN MESOZOIC ERA

65 MYA: TERRAN CENOZOIC ERA: Tertiary

• Archean Era - Text by M. Alan Kazlev
  The second major geological era in the history of Earth, following the Hadean and preceding the Proterozoic. Representing typical eogaian conditions, it was characterized by a reducing atmosphere, the presence of micro-organisms only, and extensive volcanic activity.
  
• Archivists  - Text by Richard Baker
  Vanished builders of certain hi-tech objects.
  
• Auld Limner  - Text by Peter Kisner, M. Alan Kazlev and Anders Sandberg
  Perseus Arm (and possibly also Outer Arm) space-faring predecessors of the Limners.
  
• Black Acropolis  - Text by Anders Sandberg
  A Dyson swarm built by a vanished civilization that has since been colonised by a number of other species.
  
• Cambrian Period  - Text by M. Alan Kazlev; some additions by Stephen Inniss
  Old Earth geological period, 542 to 488 million years ago; the first period of the Paleozoic era. It was followed by the Ordovician period. Well known for the "Cambrian Explosion", the relatively sudden appearance of larger and more complex organisms.
  
• Carboniferous Period  - Text by M. Alan Kazlev
  Old Earth geological period, 359 to 299 million years ago, the second last period of the Paleozoic era; it was preceded by the Devonian and followed by the Permian.
  
• Cenozoic Era  - Text by Stephen Inniss, after the original by M. Alan Kazlev
  According to some authorities, the era in Old Earth's geologic history from 65 million years ago to the present; according to others, the period from 65 million years ago until the Great Expulsion. It was preceded by the Mesozoic, and followed according to some by the Gaiazoic. During this time Old Earth took on its "modern" aspect; it is sometimes called the "Age of Mammals".
  
• Cretaceous Period  - Text by M. Alan Kazlev; some additions by Stephen Inniss
  The third period of the Mesozoic Era, from 145 to 65 million years ago; a continuation of the Jurassic heyday of the dinosaurs. It ended in a major extinction event that was also the close of the Mesozoic and the beginning of the Cenozoic.
  
• Cybyota  - Text by Steve Bowers
  Mechanical/biological world-seeding and terraforming agents of non-Terragen origin that have apparently evolved into independent life forms since their origin.
  
• Devonian Period  - Text by Stephen Inniss
  In the paleontology of Old Earth, approximately 416 to 359 million years ago; the period of the Paleozoic Era between the end of the Silurian and the beginning of the Carboniferous. More generally and informally, any gardenworld or hab space that seems similar in the array of plant and animal species might be referred to as "Devonian".
  
• Doreen/Doreens  - Text by Stephen Inniss, expanded and amended from original material by Anders Sandberg
  Chlorine world, former home of the extinct Doreens.
  
• Eocene Epoch  - Text by M. Alan Kazlev and Stephen Inniss
  On Old Earth, the second epoch of the Tertiary period and Cenozoic era, lasting from 57-34 million years ago. It was preceded by the Paleocene, and followed by the Oligocene.
  
• First Plague, The (To'ul'h Prime)  - Text by James Rogers
  Plague in ancient To'ul'hian historical times.
  
• Gaiacene Epoch - Text by Stephen Inniss
  A term used to designate the new geological epoch and ice age on Old Earth from the Technocalypse and the Great Expulsion onwards. Preceded by the Holocene.
  
• Gaiozoic Era - Text by M. Alan Kazlev
  Used to designate the geological period on Earth from the Great Expulsion onwards. Some prefer to imply a shorter time span, given the implications of the Fermi Paradox, and refer to this period as the Gaiacene Epoch.
  
• Galactic History  - Text by M. Alan Kazlev
  Branch of science and school of philosophy dealing with the history of mindkind in the Galaxy as a whole.
  
• Geological Time, Geological Time Scale - Text by M. Alan Kazlev
  The history of a Terrestrial Class planet in terms of its formation and major stages of development. It is usually measured in many millions of years. The divisions used (from the largest (longest time) to the smallest (shortest time period) are: eon, era, period, epoch, and age.
  
• Halogenics  - Text by Stephen Inniss
  The Halogenics are a hypothetical clade or group of clades, now believed to be extinct. They seeded a large number of chlorine worlds about 780 million years ago.
  
• Holocene Epoch - Text by M. Alan Kazlev and Stephen Inniss
  On Old Earth the Holocene ("entirely recent") is the most recent but one epoch in geologic time, lasting from about 12,000 BT (10,000 b.c.e.) to the Great Expulsion. This brief span of time from the birth of agriculture until the end of human baseline dominance on the species' home planet was the Golden Age according to most Anthropist sects. It was preceded by the Pleistocene and succeeded by the Gaiacene.
  
• Hov's'sa  - Text by Aaron Hamilton
  Extinct Aquatic Xenosophonts.
  
• Hovssian Epoch - Text by M. Alan Kazlev
  Local epoch in the on Rho Bentharis geological timescale, characterised by the presence of proto-Hov's'sean presophonts and then full Hov's'sa and Hov's'sa civilization. It is equivalent to the earlier late Carboniferous period, about 325 to 312 million years ago
  
• Iahi Daon Empire, The  - Text by Aaron Hamilton, some comments by Steve Bowers
  Xenosophont species extinct for more than 7 million years; known only from remains on the former homeworld and from some massive generation ships.
  
• Ice Age  - Text by Steve Bowers
  Any period of prolonged and widespread glaciation on a terrestrial world.
  
• Jacks, The  - Text by Anders Sandberg; expanded by Stephen Inniss
  The Jacks (officially known as HIE233MPE) are a xenosophont species, or possibly a cluster of related species, named for a toy of ancient human baseline origin called a "Jack-in-a-box". Their name springs from the fact that they are apparently neither extinct nor extant; instead they have "popped up" several times in the past and may or may not return at some point in the future.
  
• Jesters, The (HIE156CZE)  - Text by James Rogers
  Extinct alien species known only from ancient Muuh records
  
• Jurassic Period  - Text by M. Alan Kazlev
  Geological period of the Mesozoic Era, Earth, lasting from 199 to 146 million years ago. It was preceded by the Triassic and followed by the Cretaceous.
  
• K-T Extinction - Text by M. Alan Kazlev
  Terragen mass extinction that occurred 65 million years ago, at the boundary of the Cretaceous and Tertiary periods. Caused by an asteroid or comet impact on the Yucatan Peninsula, resulting in prolonged darkness and rapid global temperature change. It resulted in the extinction of a number of important groups of animal life, including dinosaurs, plesiosaurs, mosasaurs, pterosaurs, ammonites, and several groups of plankton. Plants, small invertebrates, small reptiles and amphibians, small birds, and nocturnal mammals were not unduly affected, and large scavenging reptiles (crocodiles) also were able to survive. The K-T extinction event was a Level IV Mass Extinction.
  
• Kalpa - Text by M. Alan Kazlev
  A generalized Sophic term for a huge period or cycle of time; e.g. the life span of the cosmos. [Sanskrit - from the verbal root klrip to be in order]
  
• Labyrinth  - Text by Todd Drashner
  Mars like world toward the outer Perseus Arm, known for its alien tunnel complex.
  
• Mesozoic Era  - Text by M. Alan Kazlev
  Geological era, Old Earth, lasting from about 251 million years ago to 65 million years ago, popularly known as the Age of Reptiles (more correctly, Age of Archosaurs).
  
• Miocene Epoch  - Text by M. Alan Kazlev and Stephen Inniss
  On Old Earth, the fourth epoch of the Tertiary period and Cenozoic era, lasting from 23 to 5 million years ago. It was preceded by the Oligocene and followed by the Pliocene.
  
• Neogene Period  - Text by Stephen Inniss
  In Old Earth paleontology and geology, the second period of the Cenozoic. It began 23 million years ago, and depending on which authority one consults it either continues today or ended at the beginning of the Quaternary or ended with the Great Expulsion in 621 AT. It includes the Miocene and Pliocene epochs, and may also be considered to include the Pleistocene, Holocene, and Gaiacene.
  
• Old Earth  - Text by M. Alan Kazlev
  Generic term used to designate Earth before the Great Expulsion. As well as the literal meaning, and the reference to Terragen origins and ancient baseline history, the term has various other associated nuances, from the ridiculous or exaggerated to the romantic or sublime, including lost paradise, fool's opportunity, pre-archaiocractic human supremacy, unmoderated baseline civilization (positive or negative, depending on context and clade), natural evolution, and so on.
  
• Oligocene Epoch  - Text by Stephen Inniss
  On Old Earth, the third epoch of the Tertiary period and Cenozoic era, lasting from 34 to 23 million years ago.
  
• Ordovician Period  - Text by M. Alan Kazlev; some additions by Stephen Inniss
  Second period of the Paleozoic era on Old Earth, lasting from 488 to 444 million years ago. Preceded by the Cambrian and followed by the Silurian.
  
• Paleocene Epoch  - Text by Stephen Inniss
  On Old Earth, the first epoch of the Cenozoic Era, lasting from 65 to 57 million years ago. It was preceded by the last epoch of the Cretaceous and followed by the Eocene.
  
• Paleogene Period - Text by Stephen Inniss
  In Old Earth paleontology and geology, the first period of the Cenozoic, stretching from 65 to 23 million years before the present and containing the Paleocene, Eocene and Oligocene epochs. It was followed by the Neogene. The Muuh and the Soft Ones established interstellar civilizations during this period, and though there are ruins of Muuh origin on Titan there is no evidence they ever interacted with Earth life and the modern Muuh have no record of any connection with Solsys at all.
  
• Paleolithic - Text by M. Alan Kazlev
  The old stone age. Among Old Earth hominids the stage of development of the most primitive stone tools. Also applied to analogous stages among xenosophont tool users.
  
• Paleozoic Era  - Text by M. Alan Kazlev
  One of the main geological eras of Earth, lasting from 542 to 251 million years ago. It includes the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods.
  
• Permian Period  - Text by M. Alan Kazlev
  The final period of the Paleozoic era. Lasting from 299 to 251 million years ago, this was also known as the beginning of the Age of Reptiles. Pangea took its final shape, the great coal forests disappeared, the climate became more arid, and reptiles suplanted amphibians, gymosperms took over from pteridophytes, and more modern forms of insects appeared. The period ended with the largest natural mass extinction on Earth since the evolution of higher life-forms, and was followed by the Mesozoic Era.
  
• Pleistocene Epoch  - Text by M. Alan Kazlev and Stephen Inniss
  On Old Earth, the first epoch of the Quaternary Period, corresponding to the most recent Ice Age; 2.6 million years ago to 12,000 BT (10,000 b.c.e.) Life forms included the first anatomically modern humans, megafauna such as mammoths, mastodons, sabre toothed cats, giant ground sloths, woolly rhinos, diprotodonts, and other forms, as well as smaller animals. Invertebrates were basically the same as modern forms. A mass extinction of large mammals and many birds occurred at the end of the epoch, caused by a combination of climate change and human impact.
  
• Pliocene Epoch  - Text by M. Alan Kazlev and Stephen Inniss
  On Old Earth, the fifth and last epoch of the Tertiary period, lasting from 5 to 1.8 million years ago. Life on land included mastodons, horses, camels, sabre-toothed cats, rhinoceroses, and many other forms. Hominids (australopithecines) appeared in Africa. Modern forms of whales lived in the oceans. Invertebrates were very similar to modern forms.
  
• Proterozoic Eon - Text by M. Alan Kazlev
  Representing the "middle period" of the life-history of a Gaian Type world, with life mostly still at the microbial level. During this stage of planetary evolution, the atmosphere changes from reducing to oxygenated, the modern regime of continental drift begins, warm conditions replaced by "Snowball Earth", following that the short-lived Edicarian biota and the appearance of first metazoa (multicelluar animals). While the Earth was passing through it's Proterozoic stage, elsewhere in the galaxy, the Archivists, Mruta, Jacks, Halogenics, and very probably other significant xenosophont empires all arose and disappeared.
  
• Quaternary Period - Text by Stephen Inniss
  On Old Earth the third period (or second according to some) of the Cenozoic Era on Old Earth beginning 2.8 million years ago. It follows the Neogene (or according to some divisions the Tertiary) period, and consists of the Pleistocene, Holocene, and Gaiacene epochs.
  
• Silurian Period  - Text by Stephen Inniss
  In the paleontology of Old Earth, approximately 444 to 416 million years ago; the geologic period of the Paleozoic Era between the end of the Ordovician and the beginning of the Devonian. More generally and informally, any gardenworld or hab space that seems similar in the array of plant and animal species might be referred to as 'Silurian'.
  
• Tertiary Period  - Text by M. Alan Kazlev and Stephen Inniss
  According to some chronologies of Old Earth, the first period of the Cenozoic Era, sometimes called the age of mammals, lasting from 65 to 2.6 million years ago. It was preceded by the last epoch of the Cretaceous, and followed by the Quaternary period. This usage fell out of fashion in the Information Age and the epochs within the Quaternary were reassigned to the Paleogene and Neogene, but scholars in some times and places since have preferred the older usage.
  
• Thyresta  - Text by Anders Sandberg
  Extinct alien species, inhabited New Montana (YTS-4885002-3825-IV; MPA).
  
• Triassic Period  - Text by M. Alan Kazlev
  The first period of the Mesozoic Era, Old Earth, lasting from 251 to 199 million years ago.
  
• Ultimates, The  - Text by Anders Sandberg and M. Alan Kazlev
  A static, genetically optimized phylum of sophonts inhabiting the Black Acropolis.
  
• Unnamed species HIE300CZE  - Text by Steve Bowers
  Predatory species provolved by the Muuh; hopefully extinct.
  
• Unnamed species: HIE072CZE   - Text by Aaron Hamilton
  Species which withdrew from the Orion Arm 5.4 million years ago.
  
• Unnamed Species: HIE121CZE   - Text by Aaron Hamilton
  Xenosophonts which vanished 31 million years ago.
  
• Unnamed species: HIE636MZE  - Text by Aaron Hamilton, updated by Steve Bowers
  The first indisputable physical relic of an alien civilisation capable of extraplanetary activity, discovered in orbit around Epsilon Scuptoris A in 1465 AT by a First Federation Exploration mission.