1 . Adults tend to have stronger cognitive, social and emotional skills, which allow them to better identify with, offer advice to, and otherwise support friends. Many young adults enjoy this emotional depth along with an abundance of free time before family and career responsibilities pick up in midlife. It’s no wonder that this age is a high-water mark for friendship. Those who go to college get a few extra years of living near their peers. Later in adulthood, though, people have more demands on their time: work, romantic partnership, and caregiving all compete for their attention.

Plus, when adults enter the workforce full-time, potential new friends don’t constantly surround them the way they did in school or while living in dormitories. Though some continue to carve out time for their social lives. Bagwell said, friendship tends to become “a luxury rather than priority.”

Under these new circumstances, many people see friends less frequently — and they tend to spend the time they do have together differently. For efficiency’s sake, they might pair socializing with other activities, like sharing a meal. Though grabbing dinner with a friend can be engaging, it’s a far cry from well-planned forest ceremonies. Friends could choose to tell each other secrets at a meal, but the activity doesn’t bring about the type of natural openness that play can.

This pursuit of efficiency and the safety of following routine can come at the cost of pleasure. An efficiency mindset risks having friendships feel like making a trade, as if each meeting should be “worth it.” But squeezing time for short and rare meetings is unlikely to feel fulfilling. If you haven’t seen each other in a while, focusing on chatting about old days is natural. However, looking back on important events in life can feel like exchanging notes while joint adventures create memories—the foundation of close friendship. As the sociologist Eric Klinenberg put it, “You tend to enrich your social life when you stop, stay longer and waste time.”

3 . At 3:30 a.m. EDT on April 19, the Ingenuity helicopter --- which landed on Mars with the Perseverance rover (漫游者) in February --- took off from the Martian surface. More importantly, it circled for about 30 seconds, three meters above the surface and came right back down again.

It may not sound like a huge achievement, but it is. Ingenuity’s flight is the first powered flight of an aircraft on another planet. It marks the milestone in the story of human space exploration.

There are several technological challenges to conduct helicopter flight in another world. First, and more significantly, helicopters need an atmosphere to fly. The blades (桨叶), or “rotors” of a helicopter must spin (旋转) fast enough to generate a force called “lift”. But lift can only be generated in the presence of some kind of atmosphere. While Mars does have an atmosphere, it’s much, much thinner than Earth’s --- about 100 times thinner, in fact.

Flying Ingenuity in Mar’s atmosphere is therefore the equivalent (对等物) of flying a helicopter on Earth at a height of 100,000 feet. For reference, commercial aircraft fly between 30,000-40,000 feet above the Earth’s surface and the highest we’ve ever been in a helicopter on Earth is 42,000 feet.

Then there’s the Martian gravity to consider. It is about one-third the strength of gravity on Earth, which means we’d be able to lift Ingenuity with less power than would be required here. But while Mars’ gravity works to our advantage, this is cancelled out by the lack of atmosphere.

Even sending the signal for the flight to begin required a collection of advanced technology. While it only requires minutes for radio signals to travel between Earth and Mars, there was still a delay of hours for those signals to reach the helicopter.

All these things require Ingenuity to be light enough. Actually, it weighs less than 4 pounds, stands just 1.6 feet tall, and carries batteries, heaters and sensors. Besides, its two rotors had to spin about 2,400 revolutions per minute — five times faster than on Earth.

When in flight, Ingenuity’s shadow gives the impression of oversized, four-winged dragonfly. But the tiny craft is set to make an enormous impact on space exploration. “Sojourner’s technical exposure in 1997 gave NASA the guarantee of future pilots. What the Ingenuity team has done has given us a new chance. I think that’s the way we build the future,” said JPL director Michael Watkins. In addition, Watkins believes that Ingenuity is expected to lay the foundation for more antigravity spacecraft capable of exploring other worlds in a totally new way.

4 . The 1930s and early 1940s were a good time to fish for sardines (沙丁鱼) off California. Centered on Monterey Bay, catches increased dramatically and supported the state’s economy. But the situation began to change in 1946, and sardine catches eventually fell from an average of 234,000 tons to just 24,000 tons. The industry went belly-up.

Scientists have guessed for decades about what caused this phenomenon, but they lacked data to test their theories. Now researchers have finally found one apparent cause: cycles of ocean upwelling, a defining feature of the West Coast sea environment in which deep, nutrient-rich water rises to the nutrient-poor surface and restores the food supply there. The key that unlocked this phenomenon turned out to be old seaweed specimens (标本) gathered around the U. S.

“Plants are just sitting there, recording data about the state of the ocean,” says Kyle Van Houtan, chief scientist at the Monterey Bay Aquarium and senior author of the new study. Van Houtan and others had suspected the impact of upwelling, but scientists only started measuring the process in Monterey Bay in 1946. Historic seaweed specimens, Van Houtan realized, might fill in the blanks for earlier years—similar to the way ice cores can help reconstruct CO₂ levels from times before researchers started collecting real-time measurements.

For the new study, the scientists relied on the fact that deeper water near Monterey typically hosts more of a particular nitrogen isotope (氮同位素). Looking at modern upwelling data and recently collected seaweed, they found that higher levels of this nitrogen in the plants’ cells corresponded with periods of more upwelling. Next they measured the isotope levels in 70 historic specimens of the red seaweed Gelidium, gathered from Monterey as far back as 1878. The results suggested a gradual increase in upwelling and then a dramatic decrease, which lined up with the sardine population’s growth and decline.

“This paper is an excellent example of the creative detective work of historical ecology,” says Loren McClenachan, a marine ecologist at Colby College, who was not involved in the research. “There are thousands and thousands of similar specimens in collections around the world, and applying similar methods could teach us a great deal about long-term ocean change.”

5 . On a September afternoon in 1940, four teenage boys made their way through the woods on a hill overlooking Montignac in southwestern France. They had come to explore a dark, deep hole said to be an underground passage to the nearby manor（庄园）of Lascaux. Squeezing through the entrance one by one, they soon saw wonderfully lifelike paintings of running horses, swimming deer, wounded wild oxen, and other beings—works of art that may be up to 20,000 years old.

The collection of paintings in Lascaux is among some 150 prehistoric sites dating from the Paleolithic period（旧石器时代）that have been documented in France's Vezere Valley. This corner of southwestern Europe seems to have been a hot spot for figurative art. The biggest discovery since Lascaux occurred in December 1994, when three cave explorers laid eyes on artworks that had not been seen since a rockslide 22,000 years ago closed off a large deep cave in southern France. Here, by unsteadily shining firelight, prehistoric artists drew outlines of cave lions, herds of rhinos（犀牛）and magnificent wild oxen, horses, cave bears. In all, the artists drew 442 animals over perhaps thousands of years, using nearly 400,000 square feet of cave surface as their canvas（画布）. The site, now known as Chauvet-Pont-1'Arc Cave, is sometimes considered the Sistine Chapel of prehistory.

For decades scholars had theorized that art had advanced in slow stages from ancient scratchings to lively, naturalistic interpretation. Surely the delicate shading and elegant lines of Chauvet's masterworks placed them at the top of that progression. Then carbon dates came in, and prehistorians felt shocked. At some 36,000 years old—nearly twice as old as those in Lascaux—Chauvet's images represented not the peak of prehistoric art but its earliest known beginnings.

The search for the world's oldest cave paintings continues. On the Indonesian island of Sulawesi, for example, scientists found a large room of paintings of part-human, part-animal beings that are estimated to be 44,000 years old, older than any figurative art seen in Europe.

Scholars don't know if art was invented many times over or if it was a skill developed early in our evolution. What we do know is that artistic expression runs deep in our ancestry.

When Micah was a child, I used to do many things with her. Later, I got promoted and was always on constant business holidays. 3 years' devotion to work resulted in my absence from her life and now she was a teenage girl. Recently, I eventually managed to have abundant time to accompany her.

For the last few weeks, Micah had watched mockingbirds make a nest in a tree and lay eggs there. Sometimes, I came to accompany her without being invited. But whenever I made an attempt to break the ice, “I'm good” was about all she said to me. Code for “Leave me alone”.

“Why doesn't she want to do things with me?”I thought as I set the table for dinner one evening, hoping for an emotion bridge to reappear between us. Did she feel hurt with my long absence or feel ignored ? Lost in thought, I was seeking to mend the relationship.

“Mom!” Micah yelled suddenly. “Come quick!”

Surprised, I rushed out, only to find a little baby bird on the ground, weak and helpless. My eyes went to the branches above.

“The wind must have blown him out of the nest,”I said.

“No, it was Mr. Whiskers -our cat. You let him go outside!” Micah said, a bit annoyed.

Looking at the nest without the parents, “I'm sorry,”I said and put the bird in my palm cautiously and gently. She didn't respond, but did not refused my offer to help, either. Deciding to take care of the little baby till it became independent, I placed it in its nest. “What should we do next?” I asked. No response again. Instead, Micah went inside and hopped on her iPad. “Bird videos?” I asked. “Yes, I'm finding out what to feed it,” she said seriously.