So I'm attempting to write a scientifically accurate story and i need some help with the planets characteristics. I have a few things set up already and need some educated guesses and ideas for how the rest will work. So to start with what i have: Planet name: Remvale Radius:~8370 miles Gravity: 8.73 meters/sec Atmosphere pressure: 3.7 atmospheres Atmosphere composition: haven't decided except for around 34% oxygen Surface: 62% water 38% land So the questions i have are as follows: -Density of planet? It has roughly twice the radius of earth but a lower gravity so it will be much lighter, is the density a realistic mass? -Is the atmosphere pressure survivable for an entire human lifespan? If so what is the max pressure for normal human life and what adaptions would be needed? -Could humans adapt to live a normal lifespan in such an oxygen rich environment?(sorry this isn't astrophysics but i heard that increased oxygen levels would shorten lifespan) -What planetary events could cause a rapid increase in oxygen level? (roughly 20% in almost 1000 years?) -Would the increased atmosphere pressure cause any optical effects? (ex. venus atmosphere being impossible to see through) -What gas mixtures would be needed for life and temperatures similar to earth's to exist? (just basics like nitrogen oxygen and carbon dioxide) -What basic animal types would survive best on this planet? ( out of reptiles, birds, insects, mammals, amphibians, fish, ect.?) Sorry, i know this is a lot of questions from a lot of fields. I'm not expecting any one person to try to answer them all, feel free to do as many or as few as you want. Thanks!