National Aeronautics and Space Administration

A Brief History of High-Energy Astronomy: Before Common Era (BCE)

In Reverse Chronological Order

Apr, 4 BCE (or BC)	Chinese astronomers observe and record for about a month a `po star' towards the direction of the modern constellation of Aquila. Wang et al. (ApJ, 569, L43, 2002) argue that this `po star', unlike most others which are now believed to be comets, was actually a hypernova (an exceptional supernova like SN 1998bw which has much more kinetic energy release than the typical value), and that the soft gamma repeater SGR 1900+14 is the neutron star created in this event.
48 BCE (or BC)	Chinese astronomers observe and record a `guest star' which is now suspected to be a supernova explosion, possibly the one which produced the supernova remnant SNR 021.5-00.9 (Wang et al. 1986, Highlights of Astronomy, 7, 583).
134 BCE (or BC)	Chinese (and Greek) astronomers observe and record a `guest star' which is now suspected to be a supernova explosion, possibly the one which produced the supernova remnant RCW 103 = SNR 332.4-00.4 (Wang et al. 1986, Highlights of Astronomy, 7, 583).
240 BCE (or BC)	The first reliably recorded appearance of Halley's Comet (P1/Halley), by Chinese astronomers.
523 BCE (or BC)	Chinese astronomers observe and record a `guest star' which is now suspected to be a supernova explosion, possibly the one which produced the supernova remnant CTB 87 = SNR 074.9+01.2 (Wang et al. 1986, Highlights of Astronomy, 7, 583).
14th Century BCE (or BC)	A great new star is observed by Chinese astronomers during the Shang Dynasty and recorded on an "oracle bone of tortoise". Xu et al. (1992, A&A, 256, 483) suggest that this event "may be the first [supernova] explosion recorded by mankind" and was caused by the explosion of a massive star in the nearby Rho Oph molecular cloud, and that the effects are still visible as the gamma-ray source 2CG 353+16.
5,000 years ago	The beginning of construction of the first phase of Stonehenge (near the modern-day town of Amesbury in England). This complex of stones, pits and ditches has many alignments which, it has been argued, suggest that it was designed to be an astronomical observatory.
7,000 years ago	Construction of a circular walled compound near the modern-day town of Goseck in Germany which has been claimed to be Europe's oldest astronomical observatory, predating Stonehenge by more than 2000 years, based on features that align with winter solstice sunrise and sunset.
12,000 years ago	Beginning of the current interglacial period (the Holocene era) on the Earth, following the end of the last Ice Age.
12,900 years ago	Sudden onset of the Younger Dryas Cooling, followed by a return to Ice Age conditions for a thousand years or so. Napier (2010) argues that this Younger Dryad Boundary, which is marked by catastrophic wildfires over North America, the extinctions of 35 genera of mammals, and widespread soot, magnetic grains and nanodiamonds, was caused by the impact of a dense swarm of debris from a disintegrating large (50-100 km) short-period comet with the Earth, and that the remaining debris of this comet is still visible every late Fall as the Taurid Meteor Shower.
73,000 years ago	The Toba Supereruption, one of the Earth's largest known eruptions (called a volcanic supereruption), in which a volcano situated in Sumatra, Indonesia ejected a volume of 2800 km3 dense-rock-equivalent of magna and deposited an ash layer 6 inches thick over a large part of South Asia. It is hypothesised that there followed a decade-long 'volcanic winter' followed by a thousand year-long global cooling episode during which the populations of humans and a number of other large mammals declined precipitously.
110,000 years ago	Beginning of the Earth's Last Glacial Period, which lasted for one hundred thousand years. During this colder than average glacial period in the Pleistocene Epoch, massive ice sheets covered Canada, the northern USA, and much of northern Europe.
2.588 million years ago	Beginning of the current 'Quaternary Ice Age' or the Pleistocene Epoch on the Earth, a period of time containing 10 or more 100,000 years or longer glacial periods, separated by shorter (about 10,000 years) inter-glacial periods. Fascinatingly, the causes of the Ice ages and glacial periods are still being actively studied, although periodic changes in the eccentricity of the Earth's orbit around the Sun, the precession of the equinoxes and/or changes in the tilt of the Earth's polar axis to the plane of its orbit are leading contenders. The changes in the fraction of carbon dioxide in the Earth's atmosphere, ocean currents, atmospheric climate patterns such as El Nino, and plate tectonics are all thought to contribute to these long-timescale fluctuations in the Earth's surface temperature.
3 million years ago	A supernova explosion may have occurred nearby (10-100 parsecs), as inferred from the discovery in deep-ocean layers of the unstable isotope 60Fe which is created in significant amounts only in supernovae. Other evidence for a nearby supernova several million years go is the existence of the `Local Hot Bubble' in the interstellar medium in which the Solar System is embedded (see Fields et al. 2005 (ApJ, 621, 901) for more details on the 60Fe measurements; but also see Fitoussi et al. (2007, astro-ph preprint) for a follow-up study which fails to find 60Fe in the layers of a marine sediment deposited at this era).
35 million years ago	A 6-km diameter object strikes the eastern shore of the US in the location of the present-day Chesapeake Bay, the last large impact known to have hit the Earth, causing significant local destuction and a tsunami which may have crested high enough to have engulfed as far inland as the Blue Ridge Mountains. This impact left a crater 85 km in diameter and a layer of ejecta surrounding it rich in tektites (spherules) indicative of melted and fused rock.
65 million years ago	The K-T (Cretaceous-Tertiary: more correctly known as the K-Pg or Cretaceous-Paleogene) extinction event causes the extinction of about 50 - 70% of the species of life on the Earth, most notoriously the dinosaurs. This extinction event is widely believed to be due to the impact of a large object such as a comet or asteroid, and the 180 kilometer-diameter Chicxulub crater in Mexico's Yucatan Peninsula is generally regarded to be the impact site. For more on the origins and travails of terrestrial life (and on the search for extraterrestrial life), see NASA's Astrobiology site.
200 million years ago	The Triassic-Jurassic extinction event causes the extinction of a good fraction of the species of life on the Earth, e.g., up to 50% of marine species, and many types of archosaurs, therapsids, and large amphibians, either due to the impact of a large object, such as a comet or asteroid (a large crater in Manicouagan, Canada has been suggested as the impact site), or alternatively to a surge in volcanic activity triggered by the first stage of the breakup of the supercontinent dubbed Pangaea which injected more than 1013 tons of carbon in the form of methane into the atmosphere and caused a strong global warming event.
250 million years ago	The Permian-Triassic extinction event, also known as the "Great Dying" causes the extinction of many species of life on the Earth, e.g., 95% of marine species and 70% of land species, perhaps due to the impact of a large object such as a comet or asteroid. This is the largest such extinction event known in the history of life on earth. Recently, a 125-mile diameter impact crater has been discovered off the coast of Australia, the Bedout Structure, which appears to be the correct age and size for such an impact event (see Becker et al. 2004, Science, 304, 1469 for more details). Alternatively, a massive volcanic eruption which covered an area of several million square km with basaltic lava, the so-called Siberian Traps, the cause of which is an active area of scientific debate, has been fingered as the cause of the 'Great Dying".
360 million years ago	The transition from the Devonian to the Carboniferous periods causes the elimination of many species (about 70%) of life on the Earth. This was not a sudden occurrence but occurred over a few million years, and thus it is unlikely to have been caused by a large impact event.
440 million years ago	Two Ordovician-Silurian extinction events cause the extinction of many species of life on the Earth, perhaps due to the onset and decline of a major glaciation episode.
500 million years ago	The Cambrian-Ordovician series of extinction events cause the extinction of many species of life on the Earth, such as brachiopods, conodonts, and trilobites. Melott et al. (2004, International Journal of Astrobiology, 3, 55) have presented arguments that this extinction may have been triggered by a gamma-ray burst associated with a nearby (within 3 kiloparsecs) galactic supernova.
1.7 - 1.4 billion years ago	The intermittent operation of the first-known 'natural' nuclear fission reactors on the Earth as water inundated uranium deposits in Oklo, Gabon (West Africa). Such natural nuclear reactors cannot function today because the fraction of fissile 235U in rocks is too low for (normal) water to act as a neutron moderator.
2 billion years ago	The appearance on the Earth of eukaryotes, lifeforms with complex cells in which the genetic material is contained in distinct nuclei.
3.5 billion years ago	The beginning of life on the Earth, based on the age of the oldest known terrestrial lifeforms. This is obtained from the geological dating of fossilized bacteria, and is uncertain by +/- 0.5 billion years. For more on the origins of terrestrial life and on the search for extraterrestrial life, see NASA's Astrobiology site.
3.8 billion years ago	The end of the period of Late Heavy Bombardment of the surface of the Earth (and of the Moon) by asteroids and comets. Many (but not all) scientists in this field believe that prior, to this time, the Earth' surface was not a viable site for the sustained development of life.
4.557 billion years ago	Formation of the Earth (strictly speaking, the era by which the Earth had accumulated 64% of its present mass): accretion continued for about another 20 million years, at which time the Earth was impacted by a Mars-sized object (which has been dubbed Theia), and the Moon formed out of the ejecta.
4.567 billion years ago	Formation of the Solar System (strictly speaking, the era in which the oldest known accreted objects formed in the solar `nebula'): see Jacobsen (2003, Science, 300, 1513) for a brief discussion of the era of the formation of the Solar System and the Earth.
8 billion years ago	Formation of the first stars in the thin disk of our Galaxy, the Milky Way, as inferred from measurements of the coolest and dimmest white dwarf stars in the solar neighborhood, see e.g., Leggett et al., 1998, ApJ, 497, 294.
12.6 billion years ago	Formation of the first (oldest) stellar aggregates in our Galaxy, the Milky Way, as determined from the ages of its oldest globular clusters, and thus the lower limit to the age of the Milky Way itself, see e.g., Krauss and Chaboyer (2003, Science, 299, 65). Some individual stars in the halo of our Galaxy may be even older, e.g., the star HE 1523-0901 has been estimated to be 13.2 billion years old.
12.9 - 13.55 billion years ago	The Dark Ages of the Universe, after the hydrogen and helium ions that constitute most of its baryonic mass combined with free electrons to form neutral atoms (and the universe became transparent), and before significant numbers of stars and galaxies were formed and began to emit 'light', so that, apart from the slowly cooling CMB, there were no intrinsic sources of emission in the Universe (apart from the 21-cm hydrogen emission line, and some other weak spectral lines such as the Li I resonance line). The duration of this period of darkness has been confirmed by measurements made by NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite.
~13.1 billion years ago	Formation of the first galaxies and the start of the re-ionization of the Universe: the oldest known 'galaxies' to date are UDFj-39546284 and UDFy-38135539 , visible as faint red 'blobs' in the Hubble Ultra-Deep Field, and with estimated ages of 13.2 and 13.1 billion years, respectively (based on UDFj's photometric redshift of 10.3 and UDFy's spectroscopic redshift of 8.6).
13.77 billion years ago	Formation of the Universe, also known as the `Big Bang', according to measurements of NASA's Wilkinson Microwave Anisotropy Probe (WMAP) (Bennett et al. 2012, submitted). After 377,000 years of expansion, the universe cools enough (to ~3,000 K) so that the hydrogen and helium ions that constitute most of its baryonic mass combine with free electrons to form neutral atoms, and the universe becomes transparent: this is called the era of recombination. The photons from this era are still visible today (after being redshifted by a factor of ~1,100) as the cosmic microwave background (CMB).

Acknowledgements

Web page author: Stephen A. Drake (based on an original by Jesse S. Allen)

Web page maintainer: Stephen A. Drake