View source for Earth:Nadir crater

{{Short description|Claimed undersea impact crater in the Atlantic Ocean}}
[[File:Map and regional seismic sections showing location of Nadir Crater.jpg|thumb|Map and regional seismic sections showing location of Nadir Crater]]
The '''Nadir crater''' is an undersea feature on the Guinea Plateau in the [[Earth:Atlantic Ocean|Atlantic Ocean]], {{cvt|248|mi|km|-2}} off the coast of Guinea. It is suggested to be an [[Astronomy:Impact crater|impact crater]]. The feature is named after the Nadir Seamount, located 100 km to the south, and is around 8.5 km wide. The paper announcing the discovery of the feature was published in ''Science Advances'' in 2022.<ref name="nadir">{{cite journal |first1=Uisdean |last1=Nicholson |first2=Veronica J. |last2=Bray |first3=Sean P. S. |last3=Gulick |first4=Benedict |last4=Aduomahor |date=17 August 2022 |title=The Nadir Crater offshore West Africa: A candidate Cretaceous-Paleogene impact structure |journal=Science Advances |volume=8 |issue=33 |pages=eabn3096 |doi=10.1126/sciadv.abn3096 |pmid=35977017 |s2cid=251646087 |pmc=9385158 |bibcode=2022SciA....8N3096N }}</ref> It has been proposed that the structure be drilled to confirm/disprove the impact origin.<ref name="iodp">{{cite web |author=Uisdean Nicholson |author2=Sean Gulick |author3=Veronica Bray |author4=Tom Dunkley-Jones |author5=Christian Maerz |author6=Thomas Wagner |author7=Pim Kaskes |author8=Elisabetta Erba |author9=Cherif Diallo |author10=Thomas Davison |author11=Chris Lowery |author12=Cornelia Rasmussen |author13=Daniel Condon |date=2021 |title=Into the Nadir: a new Cretaceous-Paleogene impact structure? |url=https://www.iodp.org/docs/proposals/1138-1004-apl-nicholson-cover/file |url-status=live |archive-url=https://web.archive.org/web/20210925072853/https://iodp.org/docs/proposals/1138-1004-apl-nicholson-cover/file |archive-date=25 September 2021 |access-date=18 August 2022 |publisher=[[Organization:International Ocean Discovery Program|IODP]]}}</ref>

==Impact event==
The crater features all characteristics of an impact event: appropriate ratio of width to depth, the height of the rims, and the height of the central uplift.<ref name="cnn"/> It was formed at or near the [[Earth:Cretaceous–Paleogene boundary|Cretaceous–Paleogene boundary]] about 66 million years ago, around the same time as the [[Earth:Chicxulub crater|Chicxulub crater]].<ref name="nadir"/> Numerical simulations of crater formation suggested a sea impact at the depth of around 800 m of a ≥400-m [[Astronomy:Asteroid|asteroid]].<ref name="nadir"/> It would have produced a fireball with a radius of >5 km,<ref name="nadir"/> instant vaporization of water and sediment near the seabed,<ref name="nadir"/> [[Tsunami|tsunami]] waves up to 1 kilometer high around the crater<ref name="cnn">{{cite web |url=https://edition.cnn.com/2022/08/17/africa/asteroid-crater-west-africa-scn/index.html |title=Scientists discover a 5-mile wide undersea crater created as the dinosaurs disappeared |publisher=CNN |author=Katie Hunt |date=18 August 2022 |access-date=18 August 2022 |archive-date=18 August 2022 |archive-url=https://web.archive.org/web/20220818145609/https://edition.cnn.com/2022/08/17/africa/asteroid-crater-west-africa-scn/index.html |url-status=live}}</ref> and substantial amounts of greenhouse gases released from shallow buried black shale deposits.<ref name="nadir"/> A magnitude 6.5–7 earthquake would have also been produced.<ref name="eos" /> The estimated energy yield would have been around 2×10<sup>19</sup> Joules (around 5000 megatons).<ref name="nadir"/> 

To constrain the age of the crater, which now has an uncertainty in the structure's age of about one million years, and to confirm the impact nature of the event, drilling sediment cores from the crater and testing of minerals from the crater floor is key and has been proposed.<ref name=eos>{{cite web |last1=Kornei |first1=Katherine |title=Impact Crater off the African Coast May Be Linked to Chicxulub: The underwater crater, spotted serendipitously in commercial observations of seafloor sediments, is believed to have formed at roughly the same time as the famous Cretaceous-Paleogene impact event |url=https://eos.org/articles/impact-crater-off-the-african-coast-may-be-linked-to-chicxulub |website=eos.org |access-date=22 September 2022 |date=19 September 2022}}</ref><ref name="iodp" />

==Impactor==
The impactor is estimated to be around 400 m in diameter, roughly equivalent to the size of the Bennu asteroid.<ref name="nadir"/> The authors of the paper speculated that it may have been part of a [[Astronomy:Binary asteroid|binary asteroid]] with the Chicxulub impactor or part of an impact cluster, but it is also probable that is unrelated.<ref name="nadir" /> Impacts similar in size to Nadir occur on average every 50,000 to 100,000 years.<ref>{{Cite news |last=Andrews |first=Robin George |date=2022-08-17 |title=African Crater Adds an Asteroid Strike to the Late Dinosaur Era |language=en-US |work=The New York Times |url=https://www.nytimes.com/2022/08/17/science/crater-dinosaurs-africa.html |access-date=2022-08-23 |issn=0362-4331}}</ref>

==References==
{{reflist}}

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[[Category:Possible impact craters on Earth]]

{{Sourceattribution|Nadir crater}}