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Prehistoric Scratchpad

News by time period.
Most news from Science Daily
See also News by Classification.

Phanerozoic Eon (542 - 0 MYA)[]

The current geological eon, and the one where abundant animal life is present.

Cenozoic Era (65 - 0 MYA)[]

The current era. The age of mammals.

Quaternary Period (2.5 - 0 MYA)[]

The current Period. The age of humans. This time is the "current ice age", the Quaternary Glaciation.

Holocene Epoch (11.7 - 0 TYA)[]

The current epoch. The age of modern man. The current interglacial of the Quaternary Glaciation. Animals Extinct in the Modern Era:

  • Tasmanian Tiger - The top predator on Tasmania. Extinct about a hundred years ago. Resembles a tiger due to its stripes. Males also have pounches.
  • Madeiran Scops Owl - A recently discovered owl in the Madeiran islands off the coast of Portugal. It is thought that the arrival of humans in the 17th Century and the introduction of non-native species drove its extinction.

Precipitation Impacts Glacial Melt, Patagonian Glacier Study Suggests

Pleistocene Epoch (2.5 MYA - 11.7 TYA)[]

The previous epoch. Includes the beginning of the Quaternary Glaciation, several inter-glacials, up until the beginning of the current interglacial.

Tarantian Age (126 - 11.7 TYA)[]

The Late Pleistocene. Defined as the beginning of the Eemian Interglacial until the end of the last glacial period of the last ice age.
Event: Bølling Warming - Warming that gave rise to the Bølling-Allerød Interstadial, also known as Meltwater Pulse 1A. 1st of 9 pulses, the last which was 9000 YA. Precipitated by a collapse of ice shelves that caused a 14 meter rise in ocean levels and 15C rise in temperatures in a few tens of decades.

Rising CO2 Caused Rising Temperatures at End of Last Ice Age (20-10 TYA)

CO2 was hidden in ocean during last ice age (20 TYA):


  • Giant Hutias (Family Heptaxodontidae) - Extinct family of giant rodents found in the West Indies. Some are as large as beavers or black bears.
  • Cyprus Dwarf Elephant - A tiny elephant found on Cyprus. Closely related to the Asian Elephant. Used as an example of studying the Island Rule.
  • Sticklebacks - Small migratory fish. Colonized newly available freshwater lakes at the end of the last ice age. Scientists have mapped out the genes that were altered for this adaption which occurred many places in the world simultaneously and repetitively.
Ionian Age (781 - 126 TYA)[]

The Middle Pleistocene. Neanderthals developed in this era (400 TYA). The earliest known human DNA dates to this time as does the beginning of the extinction of large mammals (132 TYA).

  • Polar Bears - Bears adapted for cold climate, derived from Black Bears. The largest land predator and largest bear with the Kodiak. Hunt seals and spend most of their life on sea ice. Mitochondrial DNA research suggested they evolved only Late Pleistocene. New research from DNA from both parents show that it evolved much earlier, in the Middle Pleistocene, and that they had mixed with Brown Bears again more recently.

Neogene Period (23 - 2.6 MYA)[]

Second of 3 periods of Cenozoic.

Paleogene Period (65 - 23 MYA)[]

Earliest part of the Cenozoic.

Eocene Epoch (65 - 56 MYA)[]

Second part of the Paleogene. Began with period of global warming followed by an extinction event, followed by the "dawn" of many orders of mammals. These mammals entered North America from Europe over a land bridge. Creation of south polar current caused global cooling and led to the Oligocene extinction.

  • Primates - Mammals with long arms.
  • Horses - Fast running odd-toed ungulate.
  • Even-Toed Ungulates - Hooved animals with 2 or 4 toes. Includes deer and cattle.
    • Deer - Even toed ungulates with antlers.
    • Cattle - The domestic cow and bull.
Paleocene Epoch (56 - 34 MYA)[]

First part of Paleogene after demise of dinosaurs. Saw an explosion of diversity of mammals, though not many of the today's types of mammals are represented in this epoch.

  • Eutherians - Broad infraclass including placental mammals and close relatives.
    • Placental Mammals - Infraclass of Mammals that contain a Placenta. They arose quickly after the demise of the dinosaurs, the first fossils found 1000,000 years after the extinction.

Event: Paleocene-Eocene Thermal Maximum (55 MYA) - The hottest hyperthermal in the Cenozoic Eon. May have been precipitated by release of carbon into environment by melting glaciers. Occurred in sever 1.2 MY cycle where the earth is both eccentric and tilted, causing maximum direct sunlight at Earth's circumpolar regions.

Article: Diversity Aided Mammals’ Survival Over Deep Time

Mesozoic Era (250 - 65 MYA)[]

"Middle life" era. Age of reptiles.

Cretaceous Period (145 - 65 MYA)[]

The end of the age of Dinosaurs.

Fires more widespread during Cretaceous than thought:

Dinosaur eggs found in Chechnya:

Late Cretaceous Epoch (99-65 MYA)[]

Second half of the Cretaceous. The last epoch of the dinosaurs and one of its greatest. In Asiamerica, Duck billed, Ankylosaurids, horned, Tyrannosaurs, Pachycephalosaurids, and Dromaeosaurs were present. Gondwanaland had different dinosaurs, including Abelisaurs and Titanosaurs. Birds began to replace Pterosaurs in the air. Didelphid marsupials and placental mammals diversified but were still small. In the sea, mososaurs, modern sharks, and polycotylid pliosaurs appeared. Long necked elasmosaurs diversified, while Ichthyosaurs went extinct. An explosion of flowering plant species occurred at the beginning.
Event: More formally known as the Cretaceous-Paleogene extinction event. The mass extinction that led to the extinction of the dinosaurs. - More formally known as the Cretaceous-Paleogene extinction event. The mass extinction that led to the extinction of the dinosaurs.

Life forms:

  • Tyrannosaurus Rex - Well known theropod predator, with particularly bone crushing teeth and jaws.
  • Unescoceratops - Recently discovered ceratops in Alberta. Its name is intended to honor UNESCO's contribution to the preservation of natural history sites.
  • Gryphoceratops - The smallest known Ceratops. Recently discovered in Alberta.
  • Albertosaurus - Common Tyrannosaurid from Alberta in Late Cretaceous. Smaller than the T-Rex. May have hunted in packs.
  • Crocodilians (Order Crocodilia)- With Birds, the only living archosaurs today. Opportunistic hunters with the hardest bite of any animal that ever existed. Appeared in the late cretaceous.
  • Bonapartenykus - A late type of Alvarezsaur, showing that this type of dinosaur survived into the late Cretaceous.
  • Edmontosaurus - Well studied duck billed dinosaur. Some stayed in the arctic circle all year round.
Early Cretaceous Epoch (145 - 100 MYA)[]

The first half of the Cretaceous. New dinosurs, such as Psittacosaurus, spinosaurids, and coelurosaurs gained prominence. Others from the late Jurassic continued. In the seas, ichthyosaurs declined. Angiosperm and Eutherian plants appeared for the first time. The middle part of the Epoch was a colder time of the Cretaceous, downy feathers may have provides some dinosaurs and birds warmth during this period.

  • Yutyrannus - The "Beautiful feathered tyrant", found in China from the Early Cretaceous. The largest feathered dinosaur known.
  • Beipiaosaurus - Formerly the largest known dinosaur with feathers. Much smaller than a Yutyrannus Huali.

Jurassic Period (199 - 145 MYA)[]

Middle part of "middle life". Followed the Triassic-Jurassic extinction event. Witnessed the breakup of the supercontinent Pangea. Forest formed along new coastlines. Dinosaurs dominated the land. The first birds appeared. Pterasaurs were in the air. Ichthyosaurs and Plesiosaurs were in the sea. Mammals also existed, but were overshadowed by Reptiles.

Late Jurassic Epoch (161.2 - 145.5 MYA)[]

Late part of Jurassic.

  • Clade Eutheria (Eutherians) - Broad infraclass including placental mammals and close relatives.
    • Species Juramaia Sinensis - The oldest known Eutherian, ancestor to today's placental mammals. Found in China. Lived in the late Triassic Period. Adapted for climbing trees.
Early Jurassic Epoch (199 - 175 MYA)[]

Epoch immediately following the Tr-J extinction event. On land, new dinosurs, heterodontosaurids, scelidosaurs, stegosaurs, and tenanurans appeared, joining the coelophysoids, prosauropods, and sauropods.

  • Ichthyosaurs (Order Ichthyosauria) - Giant marine reptiles resembling dolphins. Many gave birth to live young.

Triassic Period (250 - 200 MYA)[]

First part of "Middle Life".

  • Multituberculates (Order Multuberculata) - A group of successful rodent-like mammals that with origins in the Triassic and lasted until after the fall of the dinosaurs until they were out-competed by rodents and other mammals. The longest lived group of mammals. Ate mostly flowering plants.

Paleozoic Era (524 - 251 MYA)[]

Early age of the animals.

Permian Period (299-250 MYA)[]

Last era of the Proterozoic.

  • Mesosaurs - The earliest known marine reptile. Alligator-like in appearance. May have given live birth.

Silurian Period (444-416 MYA)[]

Third period of the Paleozoic.

Ordovician Period (488 - 444 MYA)[]

Second period of the Paleozoic.

Event: Ordovician-Silurian Extinction Event (450-440 MYA) - Second greatest animal extinction event. Likely caused by cooler climate.
Event: Hirnantian Glaciation - Hirnatian Glaciation

Life Forms:

  • Godzillus - Puzzling large life form of an unknown type found in Cincinatti. Has limbs sprouting from it in branch-like fashion.

Cambrian Period (542 - 488 MYA)[]

Period that experienced the greatest explosion in animal life. Took place after Snowball Earth and a mass extinction of the pre-cambrian complex life. Many types of modern life are represented in this period, including Arthropods (trilobites, already diverse), molluscs (sea shells), echinoderms (sea urchins, starfish), and the oldest vertebrates (Haikouichthys). The development of the complex eye is thought to have originated at this time, accelerating evolution.

Event: Cambrian Explosion - A radiation of complex life and the introduction of many hard bodied species. Many of the genera of animals started because of this. May be linked to a mechanism where mineral contents of the seas increased dramatically. Life would expel this and form shells, bones, and teeth.
Event: Early-Middle Cambrian Extinction

  • Conodonts (Class Conodonta) - Extinct Eel-like chordates. Their only physical remains are their teeth, the sharpest known of all animals. They have unusual jaws compared to other animals. Some imprints have been found. First found in the Permian and survived until the Triassic-Jurrassic extinction event.
  • Trilobites - Hard bodied bottom feeding arthropods.

Article: Did Exploding Stars Help Life On Earth Thrive?

Proterozoic Eon (2.5B - 542 MYA)[]

Eon where there was abundant microbial life in an oxygenated atmosphere.

Neoproterozoic Era (1000-540 MYA)[]

Era from which we have the first multicellular fossils.

Ediacaran Period ((635–541 MYA)[]

A period of the beginnings of complex multicellular life that coincided with a slow 1% to 10% modern level 100 MY rise in Oxygen levels. Followed the Sturtian Glaciation and saw increase in Oxygen contents due to Sturtian glaciers melting and adding nutrients to the sea floor. Oxygen went from 1% to present day (enough to support small sponge-like creatures) to 10% in 100 Million Years (shortly into Cambrian). A relatively mild glaciation interrupts this period, after which oxygen levels rose again, and strange pizza-shaped creatures lived on the seafloor.
Event: Gaskiers Glaciation (582-580 MYA) - Perhaps the most recent snowball Earth Period. Preceded the appearance of Ediacaran biota.
Event (over 600 MYA) - Protein Function Needed for Multicellular Life Evolved
Event: Great Oxygenation Event 2 (700-550 MYA) - Sudden increase in oxygen levels in the oceans, possibly due to glacial melting and mixing of nutrients. Preceded Ediacaran biota and Cambrian Explosion. At first, thought to be an abrupt increase, but found to be a slow one over 100 Million Years, encompassing all of the Edicarian.

Cryogenian Period (720–635 MYA)[]

A period dominated by the greatest Ice Ball Earth glaciations, with a respite between.
Event: Marinoan Glaciation (650-635 MYA) - The most severe Snowball Earth period, sometimes called "The Snowball Earth". Oxygenation occurred after this glaciation due to melting glaciers halted a decline in oxygen levels and started an increase.
Event: Sturtian Glaciation (720-660 MYA) - The longest lasting Snowball Earth period.

Mesoproterozoic Era (1.6-1.0 BYA))[]

Era that saw the development of sexual reproduction.

Paleoproterozoic Era (2.5 - 1.6 BYA)[]

Era that saw the Great Oxygenation Event, followed by the first Snowball Earth period.

Statherian Period (1.8-1.6 BYA)[]

Period that marked the beginning of the "Boring Billion" years, where oxygen levels dropped and evolution stagnated.
Event: Boring Billion (1.8-0.75 BYA) - Period where oxygen levels dropped and continued to decline and evolution stagnated. During this time, the Earth remained warm with no glaciations, despite supercontinent formation and breakup. The period shows unprecedented and unrepeated stability. Starts with development of Eukaryotes and ends with their diversification. Plate tectonics were stable during this time (little destruction of crust) and restarted at the end.

Siderian Period (2.5 - 2.3 BYA)[]

:First period of the Proterozoic Eon. The Great Oxygenation Event and beginning of the Huronian Ice Age occurred at this time.
Event: Great Oxygenation Event (2.4 BYA) - Also called the Oxygen Catastrophe. It was at this point that iron became saturated with the free oxygen released by microbial photosynthesis so that oxygen started being released into the atmosphere. This was poisonous to existing microbes and caused a great extinction. This oxygen also reacted with Methane, a strong greenhouse gas, and may have given rise to the Huronian Ice Age.

Archean Eon (4.0 - 2.5 BYA)[]

Eon where the first preserved solid rocks have been found and microbial life first formed, prior to the oxygenation of the atmosphere. It is not known if plate tectonics were active at this time.

Event: Archaean Heavy Bombardment - Archaean Heavy Bombardment

Neoarchean Era (2.8 - 2.5 BYA)[]

Latest era of the archean eon. Oxygenic photosynthesis first evolved in this era. This would give rise to the Oxygen Catastrophe at the end of the Eon.

(2.65 - 2.5 BYA) Atmosphere see-saws between hazy and haze free.

(2.7 BYA) Fossil Raindrops Point to Greenhouse Gasses in Early Earth Rather than Higher Atmospheric Pressure

New Light Shone On Photosynthesis

Life forms:

  • Phylum Cyanobacteria (Cyanobacteria) - The oldest organisms known to undergo photosynthesis that creates oxygen. Responsible for the initial oxygenation of the planet. An endosymbiont with Algae and Plants that provides them with the ability to photosynthesis.
  • Algae (Algae) - Single cell organisms that use photosynthesis.

Paleoarchean Era (3.6 - 3.2 BYA)[]

Earliest period with evidence of life.

Strange Cousins: Molecular Alternatives to DNA, RNA Offer New Insight Into Life’s Origins

Event: Late Heavy Bombardment (3.8 BYA) - Latest period of heavy cratering in the inner solar system, as determined from Lunar impacts. Possibly caused by a perturbation of the outer planets. Comets that held life's building blocks may have delivered them to Earth, thus seeding the planet at this time. The Earth's entire surface may have been obliterated during this period, offering an alternative theory to why no older rocks could be found before this time, than that the Earth was molten until the end of the Hadean, since the Earth should have cooled off long before then.

Hadean Eon (4.54 - 4.0 BYA)[]

Eon on Earth before solid land took form, essentially molton, before the earliest preserved rocks. A proposed beginning would be the impact that formed the Moon. It is believed there was no life during this time period, or, if there was, it would have lasted long and would have to reinvent itself.

(4 BYA) Unusual amino acids from meteor set stage for L-geometry

Organics easily formed in grains of ice in outer solar system by ultraviolet radiation from neighboring stars.

(4.5 BYA) Scientists refine Earth's clock

Event: Tellus-Theia Collision (4.5 BYA) - According to the Giant Impact Theory, the Moon was formed when a Mars sized protoplanet Theia collided with the proto-Earth Tellus, which also created today's Earth.

Chaotian Eon[]

Chaotian Eon (4.68-4.5 BYA) - A proposed Eon marking the beginnings of Earth as a planet up until the collision that formed the Moon. A later 2012 proposal divided this Eon between the Hadean and Prechaotian Eons.