High on the top of California's White Mountains, the hard conditions make it difficult for life to take root. But for a certain type of tree — and for those who have travelled here to study it — this place is a perfect place.

These bristlecone pines are the oldest individual trees in the world. Researchers like Andy Bunn have come to learn from the ancients. "It's remarkable to sit here and have your hand on one of these trees and know that it was growing when the Pyramids were built." Bunn added.

"By studying samples (样本) from the trunks, it's possible to discover their hidden history. Each annual tree ring is like a time capsule of the environment for that year from which it was formed," said Matt Salzer, a scientist at the University of Arizona's Laboratory of Tree Ring Research. "And it contains many different types of information — chemical information, the information on growth, and climate information."

"If you're trying to look at people in the past through time, tree rings give you a way to do it in a way that makes sense in a human life," said University of Arizona Professor Charlotte Pearson. She first became fascinated with the bristlecones after reading about an ancient volcanic eruption on the Greek island of Santorini. "It blew my mind that trees on the other side of the world could possibly be used to date this thing within a single year," she said excitedly.

The oldest known living bristlecone is estimated to be over 4, 800 years old. For Bunn, the climate record written in the rings offers guidance for how we might think about what's happening in the present as we plan for the future. "What we're seeing increasingly is that a lot of the climate events that we are experiencing and living through right now have no example in the paleoclimate (古气候) record," he said. “So, we really are moving into unknown field."

Smile, you’re on body cam

As camera technology gets smaller and cheaper, it isn’t hard to imagine a future where we’re all filming everything all the time, in every direction.

Would that be a good thing? There are some obvious potential upsides. If people know they are on camera, especially when at work or using public services, they are surely less likely to misbehave. Another upside is that it would be harder to get away with crimes or to escape from blame for accidents.

Body-cam data could also create a legal minefield. Arguments over the truth and interpretation of police footage(影像) have already surfaced. Eventually, events not caught on camera could be treated as if they didn’t happen. Alternatively, footage could be faked or doctored (伪造) to avoid blame or do wrong to others.

Of course, some people think that if you are not doing anything wrong, you have nothing to fear. But most people have done something embarrassing, or even illegal, that they regret and would prefer hadn’t been caught on film. People already remove their social media feeds or avoid doing anything wrong in public — for fear of damaging their reputation.

The always-on-camera world could even threaten some of the qualities that make us human. We are natural persons who enjoy talking about other people’s private lives and while those might not be desirable behaviours, they oil the wheels of our social interactions. Once people assume they are being filmed, they are likely to keep silent.

The argument in relation to body-cam ownership is a bit like that for guns: once you go past a critical threshold(临界值), almost everyone will feel they need one as an insurance policy. We are nowhere near that point yet- but we should think hard about whether we really want to say lights, body cam, action.

It’s hard to turn down hamburgers, French fries, potato chips and all of the other junk food that seem to call out to us. However, eating too much junk food can harm your body, particularly if you’re between the ages of 10 and 19.

“Junk food shapes adolescent brains in ways that weaken their ability to think, learn and remember. It can also make it harder to control impulsive behaviors,” said Amy Reichelt, a brain and nutrition specialist at Western University, Canada. “It may even up a teen’s risk of depression and anxiety.”

Reichelt and two other researchers found adolescents are more sensitive than any other age group to processed foods with a lot of fat and sugar. Adolescent brains are still developing the ability to assess risks and control actions. The prefrontal cortex is the part of the brain that tells us we shouldn’t eat chips all the time and helps us resist that urge. But this region is the last to mature - it doesn’t fully develop until we are in our early 20s. Meanwhile, teen brains get more active from rewards for a while. The parts of the brain that make us feel good when we do something pleasurable are fully developed by the teen years.

In fact, these regions are even more sensitive when we are young. That’s because dopamine (多巴胺), a natural chemical that lifts our mood when we experience something good, is especially active in adolescent brains. Therefore, the teen brain has two strikes against it when it comes to resisting junk food. “It has a heightened drive for rewards and reduced self-regulation,” said Reichelt.

So, what’s the best way to say no to junk food? Researchers suggest exercise. When we exercise, the brain’s reward system becomes less sensitive to food. Exercise also cause the body to make a protein that helps brain cells grow and boosts connections between the prefrontal cortex and other brain regions. The prefrontal cortex thus can work better to help us make wise decisions and control our impulses.