EarthArXiv does not have its own preprint RSS Feed. The Open Science Framework, on which EarthArXiv is built, hosts a general RSS Feed for all domain preprint systems. However, that feed can be filtered by keywords and/or preprint system(s). Thus, you could create a feed that alerts you only of new EarthArXiv papers.
A feed of all materials in EarthArXiv can be found in this RSS feed. If you want a more tailored RSS feed, your current option is to execute a search in SHARE, and click the RSS icon next to the search bar. This is the search that generates an RSS feed of all materials in EarthArXiv: https://share.osf.io/discover?sources=EarthArXiv. Information about SHARE can be found here, and information on subscribing to the OSF Preprint RSS Feed can be found here.