Mary is testing two stain removers to see which one works best to remove grease from a towel. She put the same amount and type of grease on each of 10 towels. She then treated
each towel with the same amount of stain remover. She used each type of stain remover on 5
towels. What is the independent variable in Mary's investigation?
the amount of grease
the number of towels
the type of stain remover
the amount of stain remover

i have to report this, it doesn't relate to biology

the oldest known insects are believed to live around 400 millions ago as suggested by the fossil records.   some plants having woody stems also evolved during this time.

after the evolution of insects the first four legged species or the tetrapods evolved in shallow freshwater habitats from the intermediate species approximately 397 million years ago. the tetrapods went on conquering the land giving rise to amphibians, reptiles, mammals and birds.

the major split in tetrapods first occurred 340 million years ago branching off from amphibians.

363 million years ago when the carboniferous period began the insects started roaming on land and taking flights, following which the four limbed tetrapods adapted in the terrestrial habitat.