Before there was any life on earth, which gas was absent from earth’s ancient atmosphere? a. nitrogen b. ammonia c. oxygen d. methane

Which organisms have pharyngeal arches that develop from all three germ layers and go through the same development stages as embryos? 1.bird 2.ladybug 3.starfish 4.snake

In general, characteristics that an organism survive and reproduce become more common over time. what mechanism of evolution causes this?

10 points a population of mice have tails. over time those mice with either really short tails or really long tails have a higher rate of survival. this will probably lead to what type of selection? a. disruptiveb. directionalc. stabilizingd. evological