【推荐1】Rock music is one of the most popular types of music today, which originated and evolved in the United States during the late 1940s and early 1950s from musical styles such as gospel, blues, jazz, along with country music. Rock was beginning to show up on gospel albums and in soul music as far back as the 1930s, but it never really stood out to gain a large following. It would take a few special people to make that happen.

Several musicians have promoted the development of the rock movement, but probably the biggest star to help begin the rock revolution was Elvis Presley. His music, looks, and dancing helped rock spread rapidly and finally became America's favorite style of music.

The early rock pioneers favored pianos and saxophones, similar to blues music. They soon started changing their ways and the guitar became a rock music staple. Rock bands in the 60s and 70s focused so heavily on the guitar that guitar solos were written into nearly every rock song. It is no exaggeration to say that rock would just not be the same without some guitar greats like Led Zeppelin.

Rock songs often described events and conflicts that most listeners could relate to through personal experience. Therefore, rock music drew a younger, more rebellious crowd. It became a way for teenagers to express themselves and they felt like they were being heard. For those not into it, rock music can be noisy, but for its fans, “the louder, the better” has been the rock and roll decree for several decades.

The popularity of rock music resulted in a powerful impact on society. It influenced daily life, fashion, attitudes and language in a way few other social developments have equaled. It also has contributed to the civil rights movement. Rock music appeared at a time when racial tensions in the United States were entering a new stage.

【推荐3】Located in the tropical rainforest of the Petén Basin in northern Guatemala, Tikal was one of the largest cities of the ancient Maya civilization during its Classic Period, which ran from approximately 200 CE to 900 CE. Although Tikal reached its height during the Classic Period, some of the architecture at the site dates back to the fourth century BCE. Unfortunately, for unknown reasons, the Mayans abandoned the city around 900 CE. Due to the growth of the jungle, archaeologists did not rediscover it until 1848. The part of the city now excavated (发掘) is quite impressive. Approximately 3, 000 sites have been uncovered and nearly 10,000 still need to be uncovered.

At the center is the Great Plaza. In time, other structures were built surrounding the Plaza. These include the North Acropolis and the Central Acropolis. The North Acropolis holds seventy slabs of stone, called stelae, which stand in a double row with altars (祭坛) set in front of them. Some are carved with images of rulers and hieroglyphs (象形文字). The Central Acropolis includes 700 feet of long buildings with many rooms, often called palaces. There are six temple pyramids, with the tallest one standing 65 meters high.

In addition to the towering temples and other unique architectural works, Tikal is well known for the carved inscriptions (碑文) and exceptional ceramics (陶器) found there. The Mayans engineered reservoir and culvert (排水渠) systems to help with the storage and usage of water. Another innovation used by the Mayans were sacbes, which were raised causeways paved with lime-based cement, connecting Tikal's ceremonial nodes.

Scientists are not sure whether war, disease, famine or some other reason caused the Mayans to leave Tikal. However, they left a part of themselves behind in the ruins. The city and surrounding area is now a protected national park, and visitors are welcome to explore the ruins. Much can be learned through seeing, touching and exploring this ancient city once inhabited by the Mayans.

【推荐1】According to new studies, many birds in the Amazon rainforest have become smaller as temperatures have increased. The difference hasn’t been obvious, but it has been significant enough that some scientists have suggested it’s a universal response to climate change.

But new research finds that the body size reductions aren’t happening across the board with some large-brained birds having much less significant changes.

For the study, researchers studied some data on about 70,000 birds that had died when they crashed into buildings in Chicago from 1978 to 2016. They added data on brain volume and lifespan (寿命) for 49 of the 52 species of migratory birds (候鸟) in the original study.

They found that birds with very large brains had reductions in overall body size that were about one-third of the reductions noted in birds with smaller brains. They thought that in birds, the species with big brains are the ones that build tools, manage to survive in tough environments, live longer, invest more time and energy into raising babies, and end up surviving better in the wild.

Researchers aren’t certain exactly how warmer temperatures might lead to decreasing body size in birds, but they are considering two possible explanations, which could even be happening at the same time. First, natural selection might be favoring birds that can dissipate heat better. This is because smaller birds have higher ratios (比例) of surface area to volume, so being small can help birds stay cool. Second, warmer summers might have less food available for birds at the time when they are feeding their babies. In that case, birds might be getting smaller because of decreased food over the years.

The findings don’t suggest that climate change is having zero impact on bigger-brained birds, but researchers believe these findings can inform us of climate change and help set conservation priorities.

【推荐2】The accelerating melting of the Himalayan glaciers threatens the water supply of millions of people in Asia, new research warns. The study, led by the University of Leeds, concludes that over recent decades the Himalayan glaciers have lost ice ten times more quickly over the last few decades than that on average since the last major glacier expansion 400-700 years ago, a period known as the Little Ice Age.

The study also reveals that the Himalayan glaciers are shrinking far more rapidly than glaciers in other parts of the world—a rate of loss the researchers describe as “exceptional”. The paper, published in Scientific Reports, made a reconstruction of the size and ice surfaces of 14, 798 Himalayan glaciers during the Little Ice Age. The researchers calculate that the glaciers have lost around 40 per cent of their area-shrinking from a peak of 28, 000 km² to around 19,600 km² today.

The Himalayan mountain range is home to the world's third-largest amount of glacier ice, after Antarctica and the Arctic and is often referred to as “the Third Pole”. The acceleration of melting of the Himalayan glaciers has significant impacts on hundreds of millions of people who depend on Asia's major river systems for food and energy.

The Himalayan glaciers are generally losing ice much faster in the eastern regions. The study suggests this variation is probably due to differences in geographical features on the two sides of the mountain range and their interaction with the atmosphere—resulting in different weather patterns.

Dr Carrivick, the leader of the study, said, “While we must act urgently to reduce and relieve the impact of human-made climate change on the glaciers and meltwater-fed rivers, the modelling of that impact on glaciers must also take account of the role of factors such as lakes and debris (杂物垃圾).”

【推荐3】A recent study in Frontiers in Sustainable Food Systems shows that tomato fruits are able to transmit alerts to their mother plant when attacked by caterpillars.

Plants have a large number of chemical and hormonal signaling pathways, which are generally transmitted through the sap (树液). Given the facts that fruits just hang from the main plant before ultimately falling off and sap typically only runs from the plant no the fruit—not back and forth between the two—it has long been unclear whether or not fruits can transmit information to the plant.

To address that question, scientists at Brazil’s Federal University of Pelotas placed tomato plants in a Faraday cage. Electrodes (电极) were attached to the ends of the plants’ branches, at the points where they connected to the fruits. Then they measured electrical responses within the branches before, during and after a 24-hour period in which the frits were attacked by caterpillars. Machine-learning-based algorithms were used to identify patterns in the signals.

It was found that there was a “clear difference” between the signals before and after caterpillar attacks. Additionally, defensive biochemical responses were observed throughout the plants’ bodies, suggesting that they had been triggered by signals sent by the fruits. The researchers gave the following explanation. The tomato fruit, sensing a nearby insect, emitted electrical signals to reach the rest of the plant. These warming impulses were received by the main plant and as a result, the rest of the plant got prepared to fight off the unwanted invaders. The tomato fruit made sure that the plant produced chemicals that were unpleasant to taste, so that hungry caterpillars stayed of the fruit.

The scientists now plan on investigating whether other fruiting plants behave in the same manner as tomatoes, and whether their fruits respond to threats other than insects. “It will be possible to detect early signs of pest presence, allowing for less aggressive control measures and more accurate insect management,” explains Niemeyer Reissig, first author of a paper on the study. “Understanding how the plant interacts with its fruits, and the fruits among themselves, may bring insights into bow to ‘manipulate’ this communication for enhancing fruit quality, resistance to pests and shelf life after harvest.”