Aclimatologist removes an ice core sample from the antarctic. she finds volcanic ash at the bottom of the core, followed by increasing amounts of dissolved oxygen as she goes to the top of the core sample. which of the following can be concluded based on this information?

after a volcano erupted, all plants in the surrounding area died.
a volcano erupted due to the increasing amount of oxygen in the atmosphere.
as the amount of oxygen in the atmosphere decreased, a volcano erupted.
a volcano erupted, followed by a period of increased oxygen in the atmosphere.