Designing efficacious norovirus vaccines remains a major challenge due to several factors:
(1) the extreme genetic variability within the norovirus family and within genogroups
(2) the rapid evolution of antigenically dissimilar pandemic GII.4 norovirus strains
(3) the lack of lasting immunity upon natural exposure to noroviruses in at least a proportion of the population.
The correct answer is Oxygen.
The surface of the Earth was liquefied. As the Earth cooled, an atmosphere generated primarily from gases erupted from volcanoes. It constituted methane, hydrogen sulfide, and ten to 200 times as much as carbon dioxide in comparison to today's atmosphere.
It was considered that there was an extreme volcanic activity for the initial billion years of the existence of the Earth. The initial atmosphere was possibly majority carbon dioxide will no or little concentration of oxygen. There were slight quantities of ammonia, water vapor, and methane.
