UNIVERSITY PARK, Pa. — For billions of years single-celled organisms ruled the planet. For more than half of Earth’s history, these organisms survived in a world without oxygen, using rare sulfur for energy. Then, about 2 billion years ago, something miraculous happened: Photosynthetic organisms began splitting endlessly available water for energy and expelling oxygen. This metabolic revolution led to the rise of oxygen on our planet.

After that, in a period from 1.8 billion to 800,000 years ago, something just as miraculous happened.

Almost nothing.

This span of time during the Proterozoic Eon is known as the “boring billion” because the explosion of photosynthetic life was abruptly followed by a long pause in biological innovation. Understanding what caused this lull — and the eventual reinvigoration of evolving life — is the subject of a five-year, $975,000 National Science Foundation Faculty Early Career Development Program (CAREER) grant awarded to Miquela Ingalls, assistant professor and Wilson Faculty Fellow in the Department of Geosciences at Penn State.

Ingalls, whose career explores how life and environments responded to past global warming to better predict the future, will use a novel technique she developed to explore the abundance of phosphate — a nutrient essential to all life processes — in the ocean. Broadly, her research focuses on the role phosphate played in biological processes on early Earth.

According to Ingalls, one hypothesis proposed as to what caused the boring billion is that the biotic boom of primary producers rapidly consumed much of the planet’s available phosphate, sending the world into a phosphate-limited evolutionary hiatus. Another hypothesis suggests the boring billion ended when phosphates were released into the oceans from intense weathering of phosphate minerals on land.

Ingalls plans to test what drove these changes by sampling a series of rocks collected from four continents and three different time periods: roughly 2 billion, 1.5 billion and 700 million years ago.

“These periods represent critical intervals of Earth history where we think there are potential climatic or tectonic reasons for this influx of phosphate essentially fertilizing the biosphere,” Ingalls said. “These samples could potentially provide the missing link between sudden increases in phosphate and the breakup of supercontinents and global glaciations.”

Ingalls developed a method for tracking the availability of phosphate in the ocean. When carbonate minerals form, they leave clues as to the amount of phosphate present at that time. Using this method, researchers can roughly map out the presence of phosphate, from its abundance around 2.5 billion years ago, to its vanishing state about a billion years later.

Using these samples, Ingalls and her team will look at the time during the breakup of the supercontinent Rodinia and during an interval when Earth was thought to be entirely covered by glaciers. These tectonic and climatic extremes are both thought to have massive implications for the supply of phosphorus to the oceans.

“We’re trying to test a hypothesis that events that led to an increase in continental weathering of these phosphate minerals fed life in the shallow oceans, and thus the evolution of those first primary producers, and eukaryotic life, and eventually complex multicellular organisms,” Ingalls said.

A large portion of the grant — about a third — will fund another passion of Ingalls’ — increasing opportunities and exposure to the geosciences for underrepresented individuals and high school students.

Ingalls is working with teachers at State College and Penns Valley high schools to develop Earth Sciences curriculum that explores the connection between the evolution of Earth’s geosphere — the landscapes and rocks — and life. The roughly two- to three-week module will include both lectures and field studies from nearby outcrops. Ingalls’ team, in partnership with the John A. Dutton Institute for Teaching and Learning and the Center for Science and the Schools, will package the learning modules and virtual field trips to be publicly available for any high school classroom.

The goal, Ingalls said, is to help train teachers while exposing students to geobiology and other fields they’re often not exposed to until after high school. The high school students will have the opportunity to engage with Penn State faculty as well as graduate and undergraduate students.

“These high school students will be exposed to some of the questions geoscientists and geobiologists ask and potentially see what that career might look like,” Ingalls said.