Complex sentence: Usually it is the more widely spread species that fare better in extinction, and hence this unusual pattern could be explained by a GRB, which would probably devastate creatures living on land and near the ocean surface, but leave deep-sea creatures relatively unharmed.
Split into simpler sentences: Usually it is the more widely spread species that fare better in extinction, hence this unusual pattern could be explained by a GRB. This would probably devastate creatures living on land and near the ocean surface, but leave deep-sea creatures relatively unharmed.