Fossilized bones and shells reveal the story of evolution and extinction spanning the last 500 million years, but a new study broadens this timeline to nearly 2 billion years ago. This updated timeline illustrates fluctuations in species counts, providing insight into the emergence, diversification, and extinction of ancient life forms. The latest research now encompasses organisms from the Proterozoic Eon, which lasted from 2,500 million to 539 million years ago. Life during the Proterozoic was typically smaller and softer—such as sea sponges that lacked hard mineral skeletons—resulting in fewer fossilized remnants.
While ancient species may have evolved at a slower rate and persisted longer, recent findings from Virginia Tech indicate that evolution accelerated following global ice ages. This research, published in the journal Science, charts the evolutionary patterns of life that predates the dinosaurs.
In a metaphorical sense, if the world is a stage, then the appearances and disappearances of various species are documented in the geological record.
Fossils clearly depict how evolution and extinction have taken place over the last 500 million years, but a recent analysis from Virginia Tech now extends the timeline of life back nearly 2 billion years.
This new chart highlights the fluctuations in species population, offering scientists insights into the beginnings, diversification, and extinction of ancient life.
The study now incorporates life forms from the Proterozoic Eon, an era from 2,500 million to 539 million years ago. During this time, organisms were generally smaller and less rigid—like sea sponges that did not form mineralized skeletons—resulting in fewer fossilized remains.
Shuhai Xiao, a Virginia Tech geobiologist, and his team conducted a meticulous analysis of Proterozoic life diversity, utilizing a comprehensive global fossil dataset, which was published in the journal Science on December 20.
The research focused specifically on ancient marine eukaryotes—organisms with a nucleus in their cells. Early eukaryotes eventually gave rise to the multicellular organisms that heralded a new era of life on Earth, including animals, plants, and fungi.
“This represents the most thorough and current analysis of this time period,” commented Xiao, who has recently joined the National Academy of Sciences. “Notably, we employed a graphic correlation program allowing us to achieve enhanced temporal detail.”
The patterns observed in species provide essential insights into the intertwined evolution of life and the planet.
Key insights from the analysis include:
- The first eukaryotes appeared no later than 1.8 billion years ago, gradually achieving a stable level of diversity from around 1,450 million to 720 million years ago, a time often referred to as the “boring billion,” characterized by very low species turnover rates.
- During the “boring billion,” eukaryotic species might have evolved more slowly and endured for longer periods than those that followed.
- Then came a turning point: Snowball Earth, a series of dramatic temperature drops that encased the planet in ice at least twice between 720 million and 635 million years ago. As the ice melted, evolutionary activity surged, bringing an end to this dull phase.
“The ice ages significantly influenced the evolutionary trajectory regarding diversity and dynamics,” Xiao stated. “We observe rapid changes in eukaryotic species right after glaciation, which is a significant discovery.”
These observed patterns spark a number of intriguing questions, including:
- What caused the slow pace of eukaryotic evolution during the “boring billion”?
- What factors led to a faster evolutionary pace following the snowball ice ages?
- Was it environmental influences, like climate changes or increased atmospheric oxygen levels?
- Did an evolutionary arms race between different organisms encourage quicker adaptations?
Future researchers can build on these patterns to address these questions and enhance understanding of the complex interactions between life on Earth and the planet itself.
Contributors to the study include:
- Qing Tang, the lead author and former graduate student now at Nanjing University, along with former students Drew Muscente, currently at Princeton Consultants, and Natalia Bykova, now at the University of Missouri, who have worked in Xiao’s lab over the past decade.
- Collaborating researchers from the University of Hong Kong; University of California, Santa Barbara; Princeton Consultants; University of Missouri; Russian Academy of Sciences; University of California, Riverside; Chinese Academy of Sciences; and Northwest University (China).
