Gases in both Earth's atmosphere and oceans have changed over its history. Scientists noted oxygen spikes in both the oceans and the atmosphere that coincide with changes in species on Earth. They report that the first oxygen spike resulted in a change from the microscopic life forms of 635 million years ago to large algae around 551 million years ago. A second oxygen spike occurring around 550 and 542 million years ago, according to the fossil records, resulted in an increase in
A) life to land.
B) marine animals.
C) mammal species.
D) vascular plants.

D) vascular plants

Explanation:

It would most likely be vascular plants based on the sentence regarding large algae. Vascualr plants are more complex than algae, and mammal species is quite a large step up from the simple algae. The answer of marine animals follows the same logic. Life to land could be a probalbe answer, but that involves many vascular plants that could live under the water.

if your own plato the answer is b. the fern transitioned from sporophyte generation to gametophyte generation.

what are the awnser choices? i mean, without choices, it is an incompleat