The sun shines above the Earth’s horizon as the International Space Station orbited 264 miles above the Canadian province of Quebec.NASA Johnson/Handout
For people living in the northern hemisphere, the winter solstice marks the shortest day of the year – that is, the 24-hour period with the least amount of daylight.
But while the timing of sunrise and sunset is a well-understood consequence of Earth’s motion around the sun and the tilt of its axis, the length of time it takes Earth to complete one rotation is another matter.
Scientists agree that Earth’s spin has slowed dramatically over the eons. Evidence suggests that some three billion years ago the length of a day was closer to 16 hours. What scientists disagree over is exactly how the transition from shorter to longer days occurred.
In particular, this year saw the publication of two separate studies, each claiming the length of a day was fixed at about 19 hours for much of Earth’s history.
What makes the idea intriguing is that during this interval – dubbed the “boring billion” – microbial life on the planet seemed to have been similarly stuck in a rut. Only when the length of a day finally resumed increasing, some 600 million years ago, did life get bigger and more complex, with the emergence of the first animals.
If this is indeed what happened, the evidence should be written in the rocks of the Northwest Territories, said Norman Murray, a professor with the Canadian Institute for Theoretical Astrophysics in Toronto and a co-author of one of the studies, published in the journal Science Advances.
“That’s what got me excited about this,” Dr. Murray said. “We may actually be able to tell the difference” between one version of events and another.
Duelling tides
Ocean tides are primarily dictated by the gravitational pull of the moon. A separate “thermal tide” in the atmosphere is the result of solar heating. Between one and two billion years ago, the combined influence of the two tides could have locked Earth’s rate of rotation into a constant 19-hour day.
Oceanic
high tide
Direction of
rotation
Atmospheric
high tide
Drawing is schematic and
not to scale
ivan semeniuk and john sopinski/the globe and mail,
Source: nature geoscience, mitchell & kirscher
Duelling tides
Ocean tides are primarily dictated by the gravitational pull of the moon.A separate “thermal tide” in the atmosphere is the result of solar heating. Between one and two billion years ago, the combined influence of the two tides could have locked Earth’s rate of rotation into a constant 19-hour day.
Oceanic
high tide
Direction of
rotation
Atmospheric
high tide
Drawing is schematic and
not to scale
ivan semeniuk and john sopinski/the globe and mail,
Source: nature geoscience, mitchell & kirscher
Duelling tides
Ocean tides are primarily dictated by the gravitational pull of the moon.
A separate “thermal tide” in the atmosphere is the result of solar heating.
Between one and two billion years ago, the combined influence of the two
tides could have locked Earth’s rate of rotation into a constant 19-hour day.
Oceanic
high tide
Direction of
rotation
Atmospheric
high tide
Drawing is schematic and
not to scale
ivan semeniuk and john sopinski/the globe and mail,
Source: nature geoscience, mitchell & kirscher
Opponents of the idea say there is already enough evidence that the day was never fixed at a particular length and that Earth has simply been slowing down at a steady rate – like a spinning top losing energy.
To understand the substance of the debate, it helps to know that the day is getting longer because of the ocean tides. As they slosh back and forth, pulled by the moon’s gravity, the tides exert friction, acting like a brake on the planet’s spin.
This picture is backed up by geological evidence. Sediment deposits record successive high tides from long ago, revealing the number of days that made up each lunar month. From this it is possible to work out how long the days were at the time.
What Dr. Murray and others contend is that long ago there was another tide influencing Earth’s rotation, in an equal and opposite way. This is known as the “thermal tide,” which is generated by sunlight heating up the atmosphere on the day side of the planet. The heating causes the air to expand and push outward, forming two bulges of cooler air on either side.
Today, the thermal tide can be detected as a slight, twice-daily rise and fall in barometric pressure around the tropics, superimposed on local weather effects. It is too subtle to have much effect on the planet. But in 1987, a study by a pair of U.S. researchers suggested the thermal tide may once have been far more pronounced due to a resonance in the acoustic waves that naturally propagate through the atmosphere. Because of their orientation with respect to the sun, thermal tides would tend to speed up Earth’s rotation and counterbalance the effect of ocean tides so the length of the day remained constant.
It is this theory that has now been revived and expanded upon by Dr. Murray and his colleagues, who used a climate model and other mathematical tools to show that Earth had an unchanging 19.5-hour day for nearly 1.6 billion years. They also point to geological evidence that they say is consistent with this view.
Interestingly, what may have finally kicked the planet out of this steady state was the breakup of a supercontinent, Rodinia, which altered erosion patterns and changed the chemistry and density of the atmosphere. In response to the changing day length, bacteria may have then begun generating more oxygen, a necessary requirement for animal life.
“That is speculation,” Dr. Murray said. “But it’s speculation that some biologists like.” As evidence, he cites a 2021 paper that draws a direct link between Earth’s spin and oxygen levels in the atmosphere.
After spending so much time on the question, Dr. Murray said he was startled to realize another group had reached a similar conclusion in a paper published at almost exactly the same time as his own.
Ross Mitchell, a researcher based at the Chinese Academy of Sciences in Beijing who led that study, said he was similarly unaware of the parallel work. “It’s interesting to see two independent lab groups come to a somewhat similar conclusion within weeks of each other,” he said.
But none of that has convinced Jacques Laskar, an astronomer with the Paris Observatory who has been studying the history of Earth’s rotation and recently co-authored a critique of Dr. Murray’s and Dr. Mitchell’s claims.
“It is not because these two papers came to the same conclusion that their conclusion is correct,” Dr. Laskar told The Globe and Mail, adding that both papers lean on unreliable geological data.
In Dr. Laskar’s view, there is no evidence for the idea that Earth once had a fixed day length or that this had any influence on evolution. He laid out his counterarguments in a presentation delivered last week to the annual meeting of the American Geophysical Union.
For his part, Dr. Murray said the only way to resolve the debate is by getting more data from rock sections of the right age. As it happens, among the best places in the world to look for those rocks is the Great Slave region of the Northwest Territories.
“I intend to do that,” he said, adding that he is now seeking funding to mount a search for clues. “If you want the ground truth, data is the way to go.”
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
