Two and a half billion years ago, the Archaean Eon ended and the Proterozoic Eon began. Trillions of prokaryote cells lived in Earth's oceans. Some of these cells could photosynthesize their energy [...]
Cats have pupils that can get bigger or smaller. Eyes start to focus light By around 550 million years ago, some kinds of worms evolved eyespots sunk into their heads to protect [...]
Fossil spider from the Cretaceous era Spiders evolved from annelid worms beginning about 540 million years ago. They were among the first land creatures with more than one cell. At about the same time, the [...]
Mosquitoes bite people: A mosquito on human skin Like bees, mosquitoes evolved from earlier flies and dragonflies about 200 million years ago, during the Jurassic period. Mosquitoes have six legs like [...]
Bee on a flower What are arthropods? Insects, spiders, crabs, and lobsters are all arthropods, so there are a lot of arthropods on Earth. Annelid worms All our biology articles [...]
