Timeline of natural history

This timeline of natural history summarizes significant geological and biological events from the formation of the Earth to the arrival of modern humans. Times are listed in millions of years, or megaanni (Ma).

Dating of the Geologic record

The Geologic record is the strata (layers) of rock in the planet’s crust and the science of geology is much concerned with the age and origin of all rocks to determine the history and formation of Earth and to understand the forces that have acted upon it. Geologic time is the timescale used to calculate dates in the planet’s geologic history from its origin (currently estimated to have been some 4,600 million years ago) to the present day.

Radiometric dating measures the steady decay of radioactive elements in an object to determine its age. It is used to calculate dates for the older part of the planet’s geological record. The theory is very complicated but, in essence, the radioactive elements within an object decay to form isotopes of each chemical element. Isotopes are atoms of the element that differ in mass but share the same general properties. Geologists are most interested in the decay of isotopes carbon-14 (into nitrogen-14) and potassium-40 (into argon-40). Carbon-14 aka radiocarbon dating works for organic materials that are less than about 50,000 years old. For older periods, the potassium-argon dating process is more accurate.

Radiocarbon dating is carried out by measuring how much of the carbon-14 and nitrogen-14 isotopes are found in a material. The ratio between the two is used to estimate the material’s age. Suitable materials include wood, charcoal, paper, fabrics, fossils and shells. It is assumed that rock exists in layers according to age, with older beds below later ones. This is the basis of stratigraphy.

The ages of more recent layers are calculated primarily by the study of fossils, which are remains of ancient life preserved in the rock. These occur consistently and so a theory is feasible. Most of the boundaries in recent geologic time coincide with extinctions (e.g., the dinosaurs) and with the appearances of new species (e.g., hominids).

The earliest Solar System

In the earliest solar system history, the Sun, the planetesimals and the jovian planets were formed. The inner solar system aggregated more slowly than the outer, so the terrestrial planets were not yet formed, including Earth and Moon.

Precambrian Supereon

Hadean Eon

Archean Eon

Eoarchean Era

Paleoarchean Era

Mesoarchean Era

Neoarchean Era

Proterozoic Eon

The Proterozoic (from c.2500 Ma to c.541 Ma) saw the first traces of biological activity. Fossil remains of bacteria and algae.

Paleoproterozoic Era

Siderian Period

Rhyacian Period

Orosirian Period

Statherian Period

Mesoproterozoic Era

Calymmian Period

Ectasian Period

Stenian Period

Neoproterozoic Era

Tonian Period

Cryogenian Period

Ediacaran Period

Phanerozoic Eon

Paleozoic Era

Cambrian Period

Ordovician Period

Silurian Period

Devonian Period

Carboniferous Period

Permian Period

Mesozoic Era

Triassic Period

Jurassic Period

Cretaceous Period

Cenozoic Era

Paleogene Period

Neogene Period

Quaternary Period

Etymology of period names

PeriodStartedRoot wordMeaningReason for name
Siderianc.2500 MaGreek siderosironref. the banded iron formations
Rhyacianc.2300 MaGk. rhyaxlava flowmuch lava flowed
Orosirianc.2050 MaGk. oroseiramountain rangemuch orogeny in this period's latter half
Statherianc.1800 MaGk. statherossteadycontinents became stable cratons
Calymmianc.1600 MaGk. calymmacoverplatform covers developed or expanded
Ectasianc.1400 MaGk. ectasisstretchplatform covers expanded
Stenianc.1200 MaGk. stenosnarrowmuch orogeny, which survives as narrow metamorphic belts
Tonianc.1000 MaGk. tonosstretchThe continental crust stretched as Rodinia broke up
Cryogenianc.720 MaGk. cryogenicoscold-makingIn this period all the Earth froze over
Ediacaranc.635 MaEdiacara Hillsstony groundplace in Australia where the Ediacaran biota fossils were found
Cambrianc.541 MaLatin CambriaWalesref. to the place in Great Britain where Cambrian rocks are best exposed
Ordovicianc.485.4 MaCeltic Ordovices Tribe in north Wales, where the rocks were first identified
Silurianc.443.8 MaCtc. Silures Tribe in south Wales, where the rocks were first identified
Devonianc.419.2 MaDevon County in England in which rocks from this period were first identified
Carboniferousc.358.9 Ma Lt. carbo coal Global coal beds were laid in this period
Permianc.298.9 MaPerm Krai Region in Russia where rocks from this period were first identified
Triassicc.252.17 MaLt. triastriad In Germany this period forms three distinct layers
Jurassicc.201.3 Ma Jura Mountains Mountain range in the Alps in which rocks from this period were first identified
Cretaceousc.145 MaLt. cretachalk More chalk formed in this period than any other
Paleogenec.66 MaGk. palaiogenos "ancient born"
Neogenec.23.03 MaGk. neogenos "new born"
Quaternaryc.2.58 MaLt. quaternarius "fourth" This was initially deemed the "fourth" period after the now-obsolete "primary", "secondary" and "tertiary" periods.

References

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See also

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