While looking for fossils in East Africa, you stumble upon a fossil hominin skull, some stone tools, and a jumble of animal bones sitting on the surface at the bottom of a hill. You know it must have eroded out from somewhere in the hill but cannot pinpoint exactly where. The hill itself is comprised of four layers of sediment, each corresponding to a different period in time - 3.4 million years ago, 2.3 million years ago, 1.5 million years ago, and 500 thousand years ago from bottom to top. Using the information given below:
Hominin skull traits: Small brain but bigger than a chimp's, bipedal, small teeth, no canine diastema.
Stone tool traits: Simple cores and flakes.
Animal bones: Most of them broken and bear carnivore tooth marks, some also have cut marks from stone tools, but these came after the carnivore teeth.
Paleoenvironment: Isotope analysis suggests the ancient environment at the site was a wooded grassland near a river.
500 thousand years ago
3.4 million years ago
1.5 million years ago
2.3 million years ago