When some of the crew of the Nostromo discovered the space jockey and the alien eggs, they didn't seem too surprised. It kind of seemed normal to them that yes, a corporation like Weyland-Yutani would want them to bring back whatever they found by responding to the signal. They don't seem apathetic, and are curious as to what is inside the egg, but it's not like a "OMG Aliens exist! This will change the human race!" type reaction.
Did humanity already encounter alien life before, or is the knowledge of the Prometheus incident well known on Earth by that time?