Downloaded by guest on September 29, 2021 www.pnas.org/cgi/doi/10.1073/pnas.2013774117 ( Liu Zhenghai a Fields D. extinctions Brian end-Devonian for triggers Supernova h u eie.Dtcigete fteln-ie radioisotopes long-lived the where of disk either Galactic thin Detecting mas- 146 the resides. of in Sun collapses extinction. concentrated the core mass are to these full due stars; likely a sive are precipitated supernovae nearby have Such would that triggered were distance” at extinctions explosions end-Devonian supernova by the to rays up that supernova for cosmic propose nearby accelerating fore ionizing a by deliver drop: damage possi- can inflict that to alternative could postulated an due that the study possibly explosion we for ozone, Here cause stratospheric rise. ble in temperature global drop a dramatic specia- coincided have a low may event evi- with extinction of extinction final Recent the boundary. in that period indicates Devonian–Carboniferous dence culminating the protracted decline, near biodiversity a 2020) events 2, in July was review resulting for Devonian (received tion 2020 29, Late July approved and The NJ, Princeton, University, Princeton Bahcall, A. Neta by Edited 66621 KS Topeka, University, Washburn 66045; Astronomy, KS and Lawrence, Physics Kansas, of University Biology, Evolutionary Estonia; Tallinn, 10143 Switzerland; Biophysics, 23, Geneva CH-1211 (CERN), Research e 61801; ihfiefigr n os h atta hs pce disappeared species tetrapods these that and fact fish, The bony toes. and sharks, fingers this intact five Crisis; left with largely Hangenberg have the chitinozoans, to with proto-trees, seems conodonts, coeval including possibly ammonites, plants acritarchs, many and trilobites, (10), of ky fish, extinctions 300 of armored about pulse after of gen- followed, loss a a a pollen by first However, and was spores there (9). that in remains emerging diversity be plant to settings seems of consensus terrestrial paucity stratigraphic eral and overall in marine the difficulties between and including and within factors, correlation several by cated any whether and occurrence. 5, their ref. for in test could data evidence the astrophysi- additional for whether well account consider as could we sources 8), Here cal ref. damage. e.g., genetic (see, direct that levels as extinction increase ozone elevated (UV-B) of trigger causes -B could possible concomitant be and to known depletion are which radiation, izing warming global of episode an depletion, LIP. to by ozone it caused linked triggered not eruption instead (LIP) volcanic 5 province that ref. igneous whereas argued large 7 malfor- a Ref. as of and years. order such the of evidence on thousands of assemblages many light palynological in in 6), persisting mations ozone ref. with also associated (see was depletion event Hangenberg the that suggested Devonian–Carboniferous the (Kellwasser (DCB) around boundary pulse event) extinction (Hangenberg an tion by followed punctuated 2), event) (1, years of T are hypothesis extinction supernova nucleosyn- the supernova of probe core-collapse tests and the discussed. possible star, to Other massive point thesis. a origin, of supernova explosion a confirm would liosCne o dacdSuiso h nvre nvriyo lios raa L61801; IL Urbana, Illinois, of University Universe, the of Studies Advanced for Center Illinois eateto hsc,KnsCleeLno,Lno CR2S ntdKingdom; United 2LS, WC2R London London, College Kings Physics, of Department h rcs atrspeaetdrn h C r compli- are DCB the during prevalent patterns precise The ion- of sources astrophysical considered not has work Previous Sm eLt eoinboiest rssi hrceie ya by millions over characterized occurring rate is speciation crisis in decline biodiversity protracted Devonian Late he c or eateto hsc,Uiest fIlni,Ubn,I 61801; IL Urbana, Illinois, of University Physics, of Department | 244 supernova Pu a,b,c,1 noeo oeedDvna xicinstrata extinction end-Devonian more or one in ∼ ∼ 359 10 | omcrays cosmic ) dinL Melott L. Adrian , a,b yltrb oemdrt extinc- moderate more a by later My yao(,4.Mrhl ta.()recently (5) al. et Marshall 4). (3, ago My es .Miller A. Jesse , ∼ h eateto hsc,Uie ttsArFreAaey ooaoSrns O80840; CO Springs, Colorado Academy, Force Air States United Physics, of Department 20 | ozone oehtbyn h “kill the beyond somewhat pc, | stp geology isotope d onEllis John , g ∼ aoaoyo ihEeg n opttoa hsc,Ntoa nttt fCeia hsc and Physics Chemical of Institute National Physics, Computational and Energy High of Laboratory a,b 0 y ethere- We ky. 100 n ra .Thomas C. Brian and , e,f,g j idvriyIsiue nvriyo ass arne S605 and 66045; KS Lawrence, Kansas, of University Institute, Biodiversity d dineF Ertel F. Adrienne , eateto hsc n srnm,Uiest fKna,Lwec,K 66045; KS Lawrence, Kansas, of University Astronomy, and Physics of Department 1 oeiaie ies . C BY-NC-ND) (CC 4.0 NoDerivatives License distributed under is article access open This interest.y B.D.F., competing and no declare data; authors paper.y analyzed The the B.C.T. wrote and B.C.T. and and Z.L., B.S.L., B.J.F., B.S.L., B.J.F., B.D.F., A.F.E., J.E., research; A.L.M., A.L.M., designed research; J.E. performed and J.A.M. 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ASTRONOMY BRIEF REPORT spring/summer. While this is likely detrimental to surface , r20 = r/20 pc from Earth. Hence a CCSN at a distance ≈ 2 times most organisms have repair mechanisms that can cope with some the “kill radius” of 10 pc is a plausible origin of the end-Devonian short-duration UV-B exposure. event(s). In contrast, the Type Ia SN rate is an order of magni- Thirdly, the effect is likely to be limited geographically, since tude smaller, as these events are spread over the ≈ 8 times larger strongly convective storms are not uniformly distributed and the volume of the thick disk. enhanced water vapor is likely only to spread over ∼ 100 km Massive stars are usually born in clusters (OB associations), horizontally (12). and are usually in binaries with other massive stars. Thus, if one Finally, there is significant uncertainty as to the ozone deple- CCSN occurred near the DCB, it is likely there were others. tion level needed to induce aberrations in pollen morphol- This could explain the Kellwasser and other enigmatic Devonian ogy and, even more critically, large-scale extinction. While the events, in addition to the Hangenberg event. anthropogenic ozone “hole” over Antarctica has led to increased UV-B exposure, no crash in the ecosystem has resulted. This may Possible Radioisotope Signatures of SNe partly be due to the seasonal nature of the change, as would be A CCSN close enough to cause a significant extinction would the case here as well. Recent work (14) has shown that short- also deliver SN debris to the Earth as dust grains—micron- term exposure to significant increases in UV-B does not result in or submicron-sized particles created early after the explosion. large negative impacts on the primary productivity of ocean phy- Grains in the explosion would decouple from the plasma (gas) toplankton, and other organisms show a wide range of sensitivity and propagate in the magnetized SN remnant until they were (15, 16). The amount of column depletion over a given location stopped or destroyed by sputtering during collisions (24). in those cases was ∼ 50%. The depletion caused by the mecha- The portion that reaches Earth would deposit in the atmo- nism considered in ref. 5 seems unlikely to be that large. Hence, sphere live (undecayed) radioactive isotopes. There is very little the convective transport of water vapor to the lower stratosphere preexisting background for radioisotopes whose lifetimes are may not be sufficient to induce a substantial extinction. It is thus much shorter than the age of Earth. Those with lifetimes com- worth considering other mechanisms for global ozone depletion. parable to the time since the event would provide suitable signatures. The discoveries of live 60Fe in the deep ocean, the Astrophysical Agents of Ozone Destruction and Biosphere lunar regolith, and Antarctic snow provide one such signal, which is interpreted as due to at least one recent nearby CCSN 2 My to Damage 3 My ago at a distance of ∼50 pc to 100 pc, which is compatible Astrophysical mechanisms for biosphere damage include bolide with the rate estimate given above (24). impacts, solar proton events, supernova (SN) explosions, Possible relic SN radioisotopes from the end-Devonian period gamma-ray bursts, and neutron star mergers (kilonovae). Bolide with an age 360 My include 146Sm (half-life 103 My), 235U (half- impacts, gamma-ray bursts and solar proton events are essen- life 704 My) and 244Pu (half-life 80.0 My). The most promising tially impulsive, and recovery of the ozone layer takes . 10 y signature may be provided by 244Pu, which has also been dis- (17), which is likely to avert lasting biosphere destruction. More- covered in deep-ocean crust and sediment samples deposited over, these events and kilonovae are unlikely to recur frequently. over the last 25 My (25). Moreover, it is absorbed into bones Accordingly, we focus on SNe. and retained during life (26), whereas uranium is absorbed Supernovae (SNe) are prompt sources of ionizing : during fossilization (27) and 146Sm is soluble. There is a sig- extreme UV, X-rays, and gamma rays. Over longer timescales, nificant 235U background surviving from before the formation the blast collides with surrounding gas, forming a shock that 235 238 of the solar system, with ( U/ U)⊕ = 0.721 ± 0.001%, so drives particle acceleration. In this way, SNe produce cos- a significant detection above this background requires deposi- mic rays, that is, atomic nuclei accelerated to high energies. 235 238 −5 tion attaining USN/ U⊕ & 3 × 10 . U-Pb dating has been These charged particles are magnetically confined inside the SN used to date the end-Devonian extinction, with an uncertainty remnant, and are expected to bathe Earth for ∼100 ky. in the 235U/238U ratio that is much larger than this target sen- The intensity would be high enough to deplete the sitivity, but even a few atoms of nonanthropogenic 244Pu in ozone layer and induce UV-B damage for thousands of years end-Devonian fossils would be unambiguous evidence for the r (18–21). In contrast to the episodic, seasonal, and geographically process in SNe. limited ozone depletion expected from enhanced convection, We have estimated the terrestrial deposition of 146Sm, 235U, ozone depletion following an SN is long lived and global (see, and 244Pu by a nearby SN. The 146Sm is a proton-rich (“ p pro- e.g., refs. 16, 20, and 21) and is therefore much more likely cess”) nucleus that might be produced by CCSNe or Type Ia SNe to lead to an extinction event, even given uncertainties around (28). Models for the p process (28) give 146Sm/144Sm ≈ 0.01 − the level of depletion necessary. [We note that, as well as the 2.5, with the predicted core-collapse abundance typically around induced UV-B damage, cosmic rays could also cause radiation 0.2. Assuming a CCSN that produced a solar 144Sm/16O ratio, 16 146 damage via muons produced when they impact the atmosphere and ejected Mej( O) = 2M , we estimate a total yield of Sm (22).] The SN blast itself is unlikely to wreak significant damage in the ejecta of N (146Sm) ≈ 1.6 × 1047 atoms. On the other on the biosphere, but may deposit detectable long-lived nuclear hand, 244Pu and 235U are neutron-rich nuclei that are made by isotopes that could provide distinctive signatures, as we discuss the rapid capture of neutrons, the r process, whose astrophysi- later. cal sites are uncertain. There is evidence that kilonovae make at There are two main types of SNe: 1) massive stars (& 8M ) least some of the lighter r-process nuclei (29), but it is uncer- that explode as core-collapse SNe (CCSNe) and 2) white dwarfs tain whether these events make the heavier nuclei of interest that accrete from binary companions and explode as Type Ia here. Assuming that CCSNe are the dominant r-process sites, SNe. These SN types have similar explosion energies, and both we estimate yields of N (235U, 244Pu) ≈ (3, 1.6) × 1047 atoms per produce able to damage the biosphere. How- explosion. ever, their different nucleosynthesis outputs lead to different The journey of SN-produced radioisotopes from explosion to radioisotope signatures. seafloor is complex. Ejecta in dust most readily reaches Earth Near-Earth CCSNe are more likely than Type Ia SNe. We esti- (30). The fraction of atoms in dust, fdust, should be high for mate the nearby CCSN frequency using a Galactic rate RCCSN = the refractory species of interest. Due to their high speeds, SN −1 (30 y) and placing the Sun at a radius R = 8.7 kpc in a thin dust grains will easily overcome the solar wind and reach Earth disk of scale radius 2.9 kpc and height 0.1 kpc (23). This gives (31). The fallout on Earth favors deposition at midlatitudes; −R /R0 3 2 3 −1 a CCSN rate RSN = e r /3R0 h0 ≈ 4 r20 Gy within additional dispersion occurs due to ocean currents (31). The

2 of 3 | www.pnas.org/cgi/doi/10.1073/pnas.2013774117 Fields et al. Downloaded by guest on September 29, 2021 Downloaded by guest on September 29, 2021 5 .C hms .J el,B .Sye,Slrirdac hne n photobiological and changes irradiance Solar Snyder, R. B. Neale, J. P. Thomas, C. productivity B. phytoplankton 15. and changes irradiance Solar Thomas, C. B. Neale, J. P. 14. Anderson G. summer: J. in levels 13. dosage UV Sayres, S. D. Smith, B. J. Wilmouth, M. D. end-Devonian Anderson, G. the J. during palynoflora 12. abnormal of Proliferation Racki, G. Filipiak, P. 11. Myrow P. 10. ilse al. et Fields flux nitrate increased The (32). wildfires increased and lightning, deposition, frequent nitrate more to lead may cascades electron Earth of bombardment effects. possible dust ion- several and and with ray begin, optical would cosmic the after the years outburst, of izing thousands or hundreds deposit Some could SNe SN for these Tests one Other of than each more then if DCB, Finally, signals. radioisotope solubility. the its before to occurred due dilution of prospective detectabil- the possible of the ity whereas of sample, resolution geological temporal available the the on the depends to detectability background Its natural material. no is there hand, prospective other the On of small. crust SN-produced Earth’s of in level ratio ground a Unfortunately, implies species. estimate each for this factors decay the including after xlso.W hsfidgoa-vrgdedDvna surface material, end-Devonian SN global-averaged of densities find thus We explosion. N lblaeaesraedniyo isotope of density surface average global .C rsini .Suos .Dnyr irpe otnna niomnsaon the around environments continental Disrupted Denayer, J. review Sautois, brief M. A Prestianni, Earth: C. and radiation 9. ionizing Astrophysical Thomas, C. B. Melott, L. A. other 8. and crisis biotic major Famennian Frasnian the for scenario radiation? volcanic ultraviolet A for Racki, role G. record-a fossil 7. the in extinction and Crises Cockell, S. Devonian- C. the 6. was radiation UV-B Wallace-Johnson, S. Troth, I. Lakin, J. Marshall, J. extinctions. 5. mass of causes the On Grasbyc, S. Bonda, D. 4. (Devonian–Carboniferous Crisis Hangenberg global The Becker, R. Aretz, M. Kaiser, S. 3. Fan X. J. Devonian Late the 2. during dynamics species invasive and collapse Speciation Stigall, A. 1. N i omcryinzto fteamshr n accompanying and atmosphere the of ray Cosmic fet tErhssraefloigatohsclinzn radiation. ionizing (2015). astrophysical 207–220 following surface Earth’s at effects events. radiation ionizing (2016). astrophysical 245–258 following ocean Earth’s in catalysis. U.S.A. bromine Sci. and Acad. chlorine Natl. via temperature and convection of observations vapour. water injected convectively from loss (2012). 835–839 ozone of risk Increased crisis. biotic implications. its and Event, Hangenberg (Famennian) event. tener (2016). the 135–145 of Introduction Boundary: Devonian-Carboniferous sources. intense intermittent of census and questions. than answers (2020). 103174 More 189, changes global Devonian Late Paleobiology mechanism. kill (2020). extinction terrestrial boundary Carboniferous Palaeoecol. extinction. (2016). mass first-order a of Review transition): biodiversity. invertebrate extinction”. “mass = ( 146 f dust Sm, ihrslto umr fCmra oEryTisi marine Triassic Early to Cambrian of summary high-resolution A al., et N ihpeiinUP g n uaino h aetDevonian Latest the of duration and age U–Pb High-precision al., et –9(2017). 3–29 478, el Q. Geol. 235 ej,i 244 1–2 (1999). 212–225 25, taopei zn vrteUie ttsi umrlne to linked summer in States United the over ozone Stratospheric al., et U, 2 usga,wihmyb eetbei fossiliferous in detectable be may which signal, Pu −t S Today GSA 244 –4(2010). 1–14 54, /t 40–41 (2017). E4905–E4913 114, 1/2 Pu) Science 146 /16π ≈ – (2012). 4–9 22, msga eed loo h degree the on also depends signal Sm f 7–7 (2020). 272–277 367, dust r 2 3) with (30), 1 ,0.3) 9, (1, O (10 Astrobiology −10 el o.Se.Publ. Spec. Soc. Geol. hc sundetectably is which ), × er.Nova Terra. t i aaoeg.Palaeoclimatol. 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Availability. ozone Data for evidence show above. signatures could other the These and Kellwasser depletion the events. for responsible additional been and have may which more, been living megafauna could they of depth. surface, extinctions at the end-Devonian near in or considered at effects be radiation surface the UV-B Earth’s comparing and to at muons addition of dose in Therefore, radiation sources. total all from surface current Earth’s the UV-B of years, at depths than at many muons oceans depth to the larger in due and much (34) dose a radiation to The matter radiation. penetrate can that dur- in increases deposits by carbon generated (32). and been wildfires have soot could in end-Devonian the increases ing pollen Any estimated on (5). data an the spores occurred by attested and this damage although radiation the DCB, before ky the 300 during of cooling stage for first evidence is the There climate. the cooling thereby to led have might ial,i hr a n CNa h C,teemyhave may there DCB, the at CCSN one was there if Finally, muons energetic produce atmosphere the striking rays Cosmic srpy.J Lett. 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