Welcome back to the Abstract! These are the studies this week that searched for the ur-animals, wandered the poles, rained on Mars, and destroyed the solar system.
First, scientists present new evidence that the first animals appeared more than 800 million years ago, a truly ancient origin that suggests our metazoan ancestors survived a period known as Snowball Earth, when our planet is thought to have been nearly completely frozen. Then: Earth’s poles won’t sit still, the sepulchral stuff of life, and a dramatically shortened lifespan for our solar neighborhood.
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I trace my ancestry to Snowball Earth
When did the first animals emerge on Earth? It’s a question that has provoked centuries of scholarly debate, and also inspired some wonderful answers in myth and legend (I’m partial to the Bible’s tidy solution: day six checklist).
The earliest animals that are clearly preserved in the fossil record lived during the Ediacara period some 574 million years ago, but the origins of our diverse metazoan family are likely much older. Now, scientists suggest that animals may have appeared on Earth a whopping 800 million years ago, during the ancient Tonian era, according to a new estimate of the dawn of animals.
“The timing of the origin of animals on Earth has puzzled scientists for centuries,” said researchers led by Orin Lole Durbin who was at the University of Oxford during this research and is now at Virginia Tech. “Unambiguous animal body fossils within the Ediacara Macrobiota provide a hard minimum calibration of 574 [million years] for crown Metazoa. Animals must have evolved before this date. Determining a maximum calibration for animals (a date at which they had not yet evolved) is a more complex task.”
Estimated timeline for the origin of animals based on molecular clock analyses. The grey bar on the right of the image is the origin of animals based on an Ediacaran upper calibration. The grey bar to the left is the origin based on older deposits in the Tonian period, as suggested by the new study. Image: Orin Lole Durbin.
The team turned to molecular clock analysis, a technique that uses the rate of genetic mutations in lineages as a rough way to reconstruct evolutionary timelines. The researchers focused on two fossil deposits—China’s Weng'an Biota and Mongolia’s Kheseen Biota, which date back 590 and 550 million years respectively—to extend the possible timeline of animals back more than 200 million years earlier.
If animals really did appear in the Tonian era, it means that our earliest metazoan ancestors survived episodes of so-called “Snowball Earth,” when our planet was almost fully covered in ice. These early critters were likely simple marine sponges and comb jellies that lived for hundreds of millions of years until their descendents exploded into the kaleidoscopic variety of animals that persist to this day.
“The possibility of a pre-Ediacaran origin and diversification of animals means we cannot discount hypotheses that link the timing of animal diversification to Cryogenian Snowball Earth glaciations,” according to the study. “The causes and trajectory of animal evolution will remain uncertain until paleontological and geochemical data provide sufficient confidence in maximum calibrations to ensure a reliable timescale.”
In short: Respect your sponge elders.
In other news…
A pole-ing error
Earth is a roiling mess of shifting continents and squishy innards, a situation that constantly throws its spin axis off balance and prompts the geographic poles to drift. This phenomenon, known as true polar wander (TPW), is distinct from Earth’s wandering magnetic poles, which are shaped by interior core-mantle processes.
Right now, TPW is clocked at a slow rate of 10 centimeters per year, but scientists have found evidence of “fast” episodes of TPW that pushed the poles off by thousands of miles over millions of years, which has knock-on effects for ocean and land distribution across the globe.
A team has now pinpointed several of these fast episodes over the past 320 million years, “confirming that protracted rapid TPW has occurred on Earth and that couplings among Earth’s rotational dynamics, mantle processes, and surface environments can be strongly episodic,” according to their study.
“These findings refute the view of TPW as negligible or persistently slow and highlight the need to consider TPW as an episodic control on sea level change and likely other global environmental and biological dynamics,” said researchers led by Mathew Domeier of the University of Oslo.
In addition to these long-term natural changes, recent human activity has slightly impacted TPW, especially the construction of dams and the glacial melt of anthropogenic climate change. So the next time you address a letter to Santa at the North Pole for your kid—or yourself, no judgement—make sure you have the most up-to-date coordinates.
It’s raining formaldehyde—formalallelujah!
Formaldehyde, the toxic chemical, has a bit of a morbid reputation—exposure to it can be fatal and it’s a common ingredient used to embalm corpses. But, paradoxically, formaldehyde (H2CO) also helped pave the way for the emergence of life on Earth as a precursor of bioessential elements such as sugars, amino acids, and nucleobases.
If life ever flourished on Mars, formaldehyde would likely also have been part of the story. To map out the possible distribution of the chemical on ancient Mars, scientists ran models of its atmosphere between 3.6 and 3.8 billion years ago, when the red planet was warmer and wetter. The results showed that formaldehyde was strongly associated with water vapor, suggesting that the chemical rained down from the ancient skies into Martian waterways.
“Significant atmospheric deposition of H2CO is observed over water bodies, including the northern ocean,” said researchers led by Shungo Koyama of Tohoku University. “We suggest that basins adjacent to persistently humid regions, which likely experienced H2CO accumulation and subsequent organic synthesis, could be potential landing sites for future missions to investigate ancient chemical evolution and whether it led to the origin of life.”
Hopefully, future missions to Mars will leave any signs of life with no place left to formalde-hide.
Update the cosmic actuary tables
I hate to be the bearer of bad news, but the solar system has been diagnosed with terminal instability and has been given a mere six billion years to live.
That’s the upshot of a new study that modelled the solar system’s future as the Sun becomes a red giant star and, ultimately, collapses into a stellar husk called a white dwarf.
Though the dying Sun will consume Mercury, Venus, and perhaps even Earth, scientists have previously assumed that the giant outer planets might be relatively unscathed by its death—perhaps surviving for up to 100 billion years after the main-sequence lights go out. But updated simulations suggest that these distant objects may be thrown into fatal chaos as early as the red giant phase, and that they are unlikely to survive more than a billion years after the Sun’s transition to a white dwarf.
“[Isaac] Newton, contemplating the drifting orbits of Jupiter and Saturn, suspected that the planetary order was mortal, and three centuries of celestial mechanics…have progressively deferred that verdict, most recently to timescales far beyond the age of the Universe,” said researchers led by Konstantin Batygin of the California Institute of Technology. “Our results return the solar system’s dissolution to astrophysically familiar territory, and relocate its cause: not the slow seep of chaos, nor the chance encounter with a passing star, but the Sun itself, which in dying does not merely enlarge the planetary system it built—it shakes it, and more often than not, spills it.”
“Newton’s envisioned instability is real after all,” the team. “He was mistaken only about the perpetrator.”
What a great story to kick off this spooky season! Planetary order is mortal, but cosmic horror is eternal.
Thanks for reading! See you next week.
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