Paleontology and geology
Diverse marine conditions dominated the northern and southern margins of the state. Tectonic activity carried blocks of continental crust northward, slamming them into southeast Alaska and causing the initial pulses of mountain building that would form the Brooks Range in northern Alaska. Extensive volcanic eruptions associated with sea-floor spreading and subduction formed a northeast to southwest belt of igneous rock in what is now central Alaska. Fossils from the Jurassic include ammonites, bivalves, and crinoids.