【推荐1】For years, scientists have been mapping this remote forest in Montana for an animal that’s extremely tricky to find. Camera traps haven’t offered convincing evidence, and even experts can’t identify its tracks with certainty. But within the past decades, researchers have developed a technique called DNA metabarcoding that can detect even the most hidden species.

The world is covered in DNA. It’s all around us — on the ground, down in the ocean and up in the clouds, which begins to break down once exposed to the environment. In 2018, scientists took a sample from some well-beaten snow tracks. Lab tests showed conclusive results: the Canada lynx (山猫) was indeed present in the area. Without seeing the cat, scientists had proof it was there because of environmental DNA or eDNA.

The process of DNA metabarcoding starts with an environmental sample like a bit of soil or the blood from leeches’ (水蛭) stomachs. Researchers use enzymes (酶) that break down cellular proteins and release DNA, which they purify. The result is a “soup” of all the DNA in the sample. Scientists then apply the polymerase chain reaction (PCR), which uses artificial DNA thread called universal primers. These primers bind to DNA sequences (序列) that are similar across species, then enlarge genetic barcodes (条形码) that are species-specific. A special device reads millions of these DNA parts. Finally, researchers compare them to reference databases and identify how many and which species are present.

This method has led to the discovery and identification of tens of thousands of species over the past decade. In Yosemite, researchers used eDNA to track and remove aggressive bullfrogs. DNA metabarcoding can also be used to monitor biodiversity. For example, using traditional approaches, categorizing all of the insects in a hectare of rainforest can take decades, but DNA from insect traps could produce these results in just a few months.

【推荐2】SpaceX launched its straight out-of-science fiction Starship several miles into the air from a remote corner of Texas on Wednesday, but the test flight ended in a fireball at touchdown.

The rocketship—50 meters tall and 9 meters wide—soared out over the Gulf of Mexico. After about five minutes, it reached an altitude of 12.5 kilometers. That's almost 100 times higher than the previous test flights. Then it turned sideways as planned and came back to Earth near the Mexican border. When it touched down, however, the rocketship exploded.

The entire flight lasted six minutes and 42 seconds. SpaceX broadcast it live on its website. Despite the crash, Musk, the owner of SpaceX, called it a “success” and tweeted, “Mars, here we come!”

SpaceX said that the rocket was precisely guided to the landing point. The fuel tank pressure was low, however, when the engines were successfully restarted for touchdown, which caused Starship to come down a little bit too fast.

Starship is actually the upper stage of Musk's moon-and Mars-ships. It will be carried on the top of a bigger rocket, known as Super Heavy, which is still in development. The entire vehicle will tower 120 meters—9.4 meters taller than NASA's Saturn V rocket that carried men to the moon almost three decades ago. SpaceX intends to use Starship to put massive satellites into orbit around Earth, besides delivering people and cargo to the moon by 2024 and Mars in 2026.

While accepting an award in Berlin last week, Musk said he's highly confident of a human flight to Mars in six years—“if we get lucky, maybe four years”. But Musk admitted for the first time after the test failure that his timelines could be too optimistic.

【推荐1】Big Basin Redwoods State Park is recovering after a natural disaster—fires heavily dam aged California’s oldest protected natural area. Lightning storms caused more than 650 fires in Northern California. But during a guided visit recently, life was reappearing on blackened red wood trees. Small flowers stood out on the burned land.

The big park usually has about 1 million visitors a year. But one year ago, many parts of the park burned for 24 hours. More than 100 structures were sabotaged , including the main part of the historic park, shelters, picnic tables and more. Many bridges were gone, too. In some places, roots are still smoking, leaving dangerous underground areas. Repair experts have been trying to identify materials and waste that need to be removed. In many ways, the park does not look much different than it did soon after fires.

Most of the ancient redwoods have survived. Astonishingly, the trees are about 2, 000 years old and among the tallest living things on Earth. The next 8 to 10 months will be spent cleaning up the park. It will be up to a year before the public can safely use the paths beyond a small coastal area.

Environmentalists have urged quick action because state officials are currently providing funds for wildfire recovery efforts and new building projects. This change provides a rare chance to get more money for public lands.

Barth is the director of Sempervirens Fund. That group started an effort in 1900 to protect 15. 5 square kilometers of redwood forest that is now in the center of Big Basin. “When Big Basin was set up, it was a sign of hope for the state park’s system, " she said. Barth added, “In this fire and rebirth, you have an opportunity again. ”Redwoods are naturally fire resistant(防火的). In old growth forests, most trees have burn marks dating back to hundreds of years.

【推荐3】A self-driving Uber vehicle struck and killed a pedestrian in a late-night accident in Tempe, Arizona, police said on Monday. The accident is believed to be the first pedestrian death involving the technology of autonomous vehicles.

The gray SUV had an operator in the driver’s seat and was traveling at about 40 miles per hour in autonomous mode when it struck a woman who was walking across the street late Sunday night, Tempe police said. The pedestrian was rushed to a hospital, where she was pronounced dead from her injuries.

“The City of Tempe has been supportive of autonomous vehicle testing because of the innovation and promise that the technology may offer in many areas, including transportation options for disabled residents and seniors,” Tempe Mayor, Mitchell said in the statement. “Testing must occur safely. All indications we have had in the past show that traffic laws are being obeyed by the companies testing here. Our city leadership and Tempe police will pursue any and all answers to what happened in order to ensure safety moving forward.”

Self-driving cars have been praised by technology companies as the wave of the future. Autonomous cars are already being in more than 30 cities around the world, with companies investing more than $80 billion into research and development.

“Everyone recognized that someone was going to die in a crash involving an autonomous vehicle eventually,” Bryant Walker Smith, a law professor at the University of South Carolina who studies risks in automated driving systems, told NBC News. “As good as that technology tries to be, mistakes can happen, or it may be one of the small fraction of crashes. I just think everybody kind of hoped that one wouldn’t come this soon.”

Smith added that because federal and state agencies don’t have the resources to monitor individual vehicles, the responsibility for safety falls on the individual companies running the technology.

The National Transportation Safety Board announced that a four-person team has been sent to Tempe to investigate the crash.