to produce proteins
chloroplasts
hydrogen gas
primates
small rat-like creatures
amino acids
slugs
it blocked sunlight
humanoids
photosynthesis
purine
birds
lightning strikes
a meteorite impact
reptiles
resource competition
via wind and water
600 million years ago
a spinal column
ability to breathe oxygen
RNA
asexual reproduction
ozone layer
aquatic environments
3.5 billion years ago
