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.”
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.
The European Space Agency is fast-tracking a new mission called Ramses, which will fly to near-Earth asteroid 99942 Apophis and join the space rock in 2029 when it comes very close to our planet — closer even than the region where geosynchronous satellites sit.
Ramses is short for Rapid Apophis Mission for Space Safety and, as its name suggests, is the next phase in humanity’s efforts to learn more about near-Earth asteroids (NEOs) and how we might deflect them should one ever be discovered on a collision course with planet Earth.
In order to launch in time to rendezvous with Apophis in February 2029, scientists at the European Space Agency have been given permission to start planning Ramses even before the multinational space agency officially adopts the mission. The sanctioning and appropriation of funding for the Ramses mission will hopefully take place at ESA’s Ministerial Council meeting (involving representatives from each of ESA’s member states) in November of 2025. To arrive at Apophis in February 2029, launch would have to take place in April 2028, the agency says.
This is a big deal because large asteroids don’t come this close to Earth very often. It is thus scientifically precious that, on April 13, 2029, Apophis will pass within 19,794 miles (31,860 kilometers) of Earth. For comparison, geosynchronous orbit is 22,236 miles (35,786 km) above Earth’s surface. Such close fly-bys by asteroids hundreds of meters across (Apophis is about 1,230 feet, or 375 meters, across) only occur on average once every 5,000 to 10,000 years. Miss this one, and we’ve got a long time to wait for the next.
When Apophis was discovered in 2004, it was for a short time the most dangerous asteroid known, being classified as having the potential to impact with Earth possibly in 2029, 2036, or 2068. Should an asteroid of its size strike Earth, it could gouge out a crater several kilometers across and devastate a country with shock waves, flash heating and earth tremors. If it crashed down in the ocean, it could send a towering tsunami to devastate coastlines in multiple countries.
Over time, as our knowledge of Apophis’ orbit became more refined, however, the risk of impact greatly went down. Radar observations of the asteroid in March of 2021 reduced the uncertainty in Apophis’ orbit from hundreds of kilometers to just a few kilometers, finally removing any lingering worries about an impact — at least for the next 100 years. (Beyond 100 years, asteroid orbits can become too unpredictable to plot with any accuracy, but there’s currently no suggestion that an impact will occur after 100 years.) So, Earth is expected to be perfectly safe in 2029 when Apophis comes through. Still, scientists want to see how Apophis responds by coming so close to Earth and entering our planet’s gravitational field.
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“There is still so much we have yet to learn about asteroids but, until now, we have had to travel deep into the solar system to study them and perform experiments ourselves to interact with their surface,” said Patrick Michel, who is the Director of Research at CNRS at Observatoire de la Côte d’Azur in Nice, France, in a statement. “Nature is bringing one to us and conducting the experiment itself. All we need to do is watch as Apophis is stretched and squeezed by strong tidal forces that may trigger landslides and other disturbances and reveal new material from beneath the surface.”
The Goldstone radar’s imagery of asteroid 99942 Apophis as it made its closest approach to Earth, in March 2021. (Image credit: NASA/JPL–Caltech/NSF/AUI/GBO)
By arriving at Apophis before the asteroid’s close encounter with Earth, and sticking with it throughout the flyby and beyond, Ramses will be in prime position to conduct before-and-after surveys to see how Apophis reacts to Earth. By looking for disturbances Earth’s gravitational tidal forces trigger on the asteroid’s surface, Ramses will be able to learn about Apophis’ internal structure, density, porosity and composition, all of which are characteristics that we would need to first understand before considering how best to deflect a similar asteroid were one ever found to be on a collision course with our world.
Besides assisting in protecting Earth, learning about Apophis will give scientists further insights into how similar asteroids formed in the early solar system, and, in the process, how planets (including Earth) formed out of the same material.
One way we already know Earth will affect Apophis is by changing its orbit. Currently, Apophis is categorized as an Aten-type asteroid, which is what we call the class of near-Earth objects that have a shorter orbit around the sun than Earth does. Apophis currently gets as far as 0.92 astronomical units (137.6 million km, or 85.5 million miles) from the sun. However, our planet will give Apophis a gravitational nudge that will enlarge its orbit to 1.1 astronomical units (164.6 million km, or 102 million miles), such that its orbital period becomes longer than Earth’s.
It will then be classed as an Apollo-type asteroid.
Ramses won’t be alone in tracking Apophis. NASA has repurposed their OSIRIS-REx mission, which returned a sample from another near-Earth asteroid, 101955 Bennu, in 2023. However, the spacecraft, renamed OSIRIS-APEX (Apophis Explorer), won’t arrive at the asteroid until April 23, 2029, ten days after the close encounter with Earth. OSIRIS-APEX will initially perform a flyby of Apophis at a distance of about 2,500 miles (4,000 km) from the object, then return in June that year to settle into orbit around Apophis for an 18-month mission.
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Furthermore, the European Space Agency still plans on launching its Hera spacecraft in October 2024 to follow-up on the DART mission to the double asteroid Didymos and Dimorphos. DART impacted the latter in a test of kinetic impactor capabilities for potentially changing a hazardous asteroid’s orbit around our planet. Hera will survey the binary asteroid system and observe the crater made by DART’s sacrifice to gain a better understanding of Dimorphos’ structure and composition post-impact, so that we can place the results in context.
The more near-Earth asteroids like Dimorphos and Apophis that we study, the greater that context becomes. Perhaps, one day, the understanding that we have gained from these missions will indeed save our planet.
