4 Footprints left behind by prehistoric people may be some of the strongest evidence yet that humans arrived in the Americas earlier than previously thought.

Over 60 tracks pop up and disappear across the landscape-show that people hung around what’s now New Mexico 23, 000 to 21, 000 years ago, geoscientist Matthew Bennett and colleagues reported in the Sept. 24 Science. If true, the fossil (化石) findings would be definitive proof that humans were in North America during the height of the last ice age, around 21,500 years ago.

When people first arrived in the Americas is highly contested. Scientists have historically thought that humans traveled across the Bering land bridge that connected Asia to North America around 13,000 years ago after the massive Laurentide Ice Sheet that once blanketed much of North America had started retreating into the Arctic. But a number of more recent discoveries from across North and South America—including roughly 30,000-year-old animal bones from a Mexican cave and stone tools from Texas-suggest that humans may have arrived far earlier.

At White Sands National Park in New Mexico, Bennett, of Bournemouth University in Pooler England, and colleagues used several methods to calculate the ages of the newly described tracks, including radiocarbon dating of plants grown in and between the footprints.

“One of the beautiful things about footprints is that, unlike stone tools or bones, they can’t be moved up or down the stratigraphy (地层).” he says. “They’re fixed, and they’re very precise.”

The tracks were created over two thousand years mostly by children and teenagers wandering through the patchwork of waterways that defined the White Sands area during the Ice Age, the researchers say.

Bennett is planning on returning to White Sands after the pandemic (疫情) to continue studying human footprints, hoping to learn more about the people who made them. “Footprints have a way of connecting you to the past that’s like nothing else,” he says. “It’s very powerful to put your finger in the base of a track and know that someone walked that way 23,000 years ago.”

Mice and rats have long been used in medical research because of their biological similarities to humans. Now, scientists have trained rats to drive small vehicles created for them. One of the main findings of the experiment was that the driving activity seemed to help the rats relax.

Researchers at the University of Richmond in Virginia led the experiment. The team built tiny cars out of plastic and other materials. The vehicles had an opening at one end where electrical wires were attached. By touching one of three different wires, the rat could control the direction of the vehicle.

Researchers trained 17 rats over several months to drive around the experiment containers. The animals proved that they could be trained to drive forward as well as in other directions to get to the sweet treats placed inside the containers.

The researchers examined levels of two hormones (荷尔蒙) in the rats—one that causes stress and another that reduces it. All rats that took part in the training had higher levels of the hormone that reduces stress. The research suggests the increased relaxation levels could be linked to the enjoyment of successfully completing a new skill. The team also found that the rats that drove themselves showed higher levels of the stress-fighting hormone than those that simply rode in small cars controlled by humans.

Lambert said the most exciting result of the experiment for her was about the possible effect on humans. The research may open new areas of non-drug treatments for people suffering from mental health conditions.

“There’s no cure for schizophrenia or depression and we need to catch up,” she said. “And I think we need to look at different animal models and different types of tasks and really respect that behavior can change our neurochemistry (神经化学). ”

Speaking to the British-based magazine New Scientist, Lambert said her team is planning to continue experiments to learn more about how the rats learned to drive. The new research will also examine why some activities appear to reduce stress, and which areas of the brain are involved in the process.

The Cardboard Box Office is a project created by Lilly and Leon Mackie, who recently moved from New Zealand to Sydney, Australia. The transfer left them with a mountain of cardboard boxes, and the arrival of their baby son Orson 10 months ago meant their social lives were “completely altered (改变.” So the couple decided to try to make some fun of the situation.

“We started after creating a one-off photo where we wanted to portray the general mess and sleep-deprivation (睡眠) that comes with being new parents,” Lilly Mackie said in an email. “People seemed to really love it and asked for more. We had a lot of weekends at home and a stockpile of cardboard so we thought ‘Why not?’ It went from there. ”

The Mackies took the first photos in September and have portrayed 14 movies so far,including their versions of “Cast Away”(or “Castababy”) and “Jurassic Park”(or “Goo-goo Gaa-gaa-rassic Park”). Even “Star Wars” gets the Mackie treatment, with Orson holding a cardboard tube in place of a saber (军刀) and mom sporting impressive Princess Leia-like hair buns ( HI       made out of brown paper in the photo titled “Wah Wars.”

The family usually creates the sets on 'Saturdays and posts the whimsical pictures on their blog and Facebook page, which have almost 3,000 fans. Besides cardboard boxes, the photos feature costumes, props (道具) , and sets created out of everyday household items, toys, “and three individuals slowly losing their sense,” they joked on their blog.

Leon, a children’s book designer at a large publishing company, and Lilly, a stay-at-home mom, are both film buffs and photography fans. The baby is also becoming a connoisseur       (鉴赏家) of movies and cardboard boxes.

“Orson seems to find the photo shoots quite fascinating and enjoys exploring the sets-and tearing things apart. There’s never a dull moment for him on Saturday nights,” Lilly said. “When he gets a little older, we’11 bring in a lot more of his input, asking for his ideas on films and sets. Make it a real family thing. I think he may come up with some quite funny things.”