What gas do some scientist think was missing from earths early atmosphere

Iwanna go do something with my ideas? ?

Which of the following explains why a tree is often used as a model to represent the principle of common descent

Which of the following best describes the expensive tissue hypothesis? brains require more energy, so the gut had to be reduced, and larger brains and tool use led to higher quality diets. increasing body size means that homo neanderthalensis had to include more fat in its diet. brains require more energy, so the gut had to be reduced as brains got bigger. brains require more fat, so the gastrointestinal viscera (gut) had to expand, and hands were needed to acquire more food.