Molecular clock analyses push the origins of animal life back by 100 to 200 million years or more. Researchers recalibrated evolutionary timelines using ancient fossil sites in Australia, Norway, and Arizona, suggesting animals may have existed well before Snowball Earth ice ages.
Animal life may have begun on Earth 800 to 700 million years ago, according to scientists tracking the timeline of earliest animal life. This estimate precedes the earliest identifiable fossil records by 100 to 200 million years or more.
Researchers tested assumptions about when complex life first emerged by examining ancient rock formations that preserve microfossils without containing actual animal remains.
Researchers Recalibrate Evolutionary Clocks
The study examined three sites with exceptionally preserved fossil assemblages dating between 850 and 730 million years ago: the Bitter Springs Group in Australia, the Svanbergfjellet Formation in Norway, and the Chuar Group in Arizona.
These evaluations determine evolutionary speeds by measuring genetic variations among modern organisms, tracing backward to deduce when precursors initially emerged.
Kheseen Biota Challenges Weng’an Assumptions
The absence of animal fossils in ancient strata has long puzzled paleontologists. Ross Anderson, an associate professor at Oxford University, former student of Earth and planetary sciences at the Yale Graduate School of Arts and Sciences, and senior author of the study, explained that the Kheseen Biota undermines the claim that Weng’an’s remarkable microfossils guarantee animal remains would appear in the collection if animals had been present back then.
Animal Origins Precede Snowball Earth
The revised chronology suggests animals existed before the glacial periods called Snowball Earth
, which purportedly commenced roughly 720 million years ago and encased the globe in ice over millennia or eons.
Scholars have long questioned if the harsh conditions tied to Snowball Earth might have hindered the pace at which animals evolved.