Wikipedia statements that failed verification: Earth and space

These are disputed statements under test, not facts this site asserts. Wikipedia editors tagged each one because the source cited for it did not appear to support it. Find what primary sources actually say and support or refute each statement as written; the cited sources listed below may be incomplete. Statement text is quoted from the linked Wikipedia articles under CC BY-SA 4.0.

1. "A cylinder seal from the Jemdet Nasr period and the Venus tablet of Ammisaduqa from the Fi..." from https://en.wikipedia.org/wiki/Venus (one source Wikipedia cited: http://ses.library.usyd.edu.au/bitstream/2123/5404/1/r-hobson-2009-thesis.pdf)

2. "Alpha Centauri may be inside the G-cloud of the Local Bubble, and its nearest known system..." from https://en.wikipedia.org/wiki/Alpha_Centauri (one source Wikipedia cited: https://doi.org/10.1051%2F0004-6361%2F201322975)

3. "Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carb..." from https://en.wikipedia.org/wiki/Albedo

4. "From October to June the surface is usually covered with sea ice in the Labrador Sea, Denm..." from https://en.wikipedia.org/wiki/Atlantic_Ocean

5. "Continents have an accepted geological definition – they are the largest landmass of a par..." from https://en.wikipedia.org/wiki/Island (one source Wikipedia cited: https://web.archive.org/web/20190716045120/https://www.nationalgeographic.org/encyclopedia/continent/)