My website's http header has weird information So I have a Drupal website. Today I checked the http headers on its homepage and found the following value:

EXPIRES Sun, 19 Nov 1978 05:00:00 GMT

I did some google research and found it's the Drupal's founder's date or something. How does it effect my site if any and how do I change this or remove it if needed? Does it effect SEO ranking as well?

Thanks!
It means you have no additional caching mechanism and the default Drupal caching will be used, several of my sites also return this header without any problem.

On other sites I use different mechanisms to control the caches, Memcache or Redis in addition with Authcache gives you quite a lot of additional control over the caches, but you'll need access to additional resources on the server.

Another aspect I've heard about is Varnish but I have no knowledge of using this myself.