We don't really know, but we do know that even if the Earth originally had an atmosphere like Jupiter's, it lost it completely when the Sun entered the T- Tauri phase as all stars of the Sun's mass do soon after birth. This phase is well known for a massive stellar wind that would have easily scoured away any primordial atmosphere like Jupiter's. What we have now is what was outgassed by the Earth after that episode, and it is an atmosphere that probably had a very different composition than either Jupiter's or the modern Earth; rich in sulfur and CO2 among other compounds.
All answers are provided by Dr. Sten Odenwald (Raytheon STX)
NASA IMAGE/POETRY Education and Public Outreach program.