Change the Permissions on a document before embedding it into your Google Site
1. In your document click Share.
This is applicable to Google Slides, Google Sheets etc.
2. In the new window, click Share with Tc.columbia.edu.
3. Click the arrow next to Tc.columbia.edu.
4. Choose which audience option you would like when this document is posted to your Google Site.
If you are making your Google Site public on the web you will want to choose the Anyone with the link option.