Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A comet could not produce the carbon-14 spike in the 8th century   A mysterious increase of radiocarbon 14C ca. 775 AD in the Earth's atmosphere
has been recently found by Miyake et al. (Nature, 486, 240, 2012). A possible
source of this event has been discussed widely, the most likely being an
extreme solar energetic particle event. A new exotic hypothesis has been
presented recently by Liu et al. (Nature Sci. Rep., 4, 3728, 2014) who proposed
that the event was caused by a comet bringing additional 14C to Earth. Here we
calculated a realistic mass and size of such a comet to show that it would have
been huge (~100 km across and 10^{14}-10^{15} ton of mass) and would have
produced a disastrous impact on Earth. Such an impact could not remain
unnoticed in the geological records and chronicles. The absence of an evidence
for such a dramatic event makes this hypothesis invalid.

5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
32
The categories of this paper are: atom-ph
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
21
The categories of this paper are: adap-org
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
13
The categories of this paper are: quant-ph
11
The categories of this paper are: hep-lat
2
The categories of this paper are: math
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph