Australia’s Great Barrier Reef has lost more than half of its corals since 1995 due to warmer seas driven by climate change, a study has found. Scientists found all types of corals had suffered a decline across the world’s largest reef system. The sharp falls came after mass bleaching(白化)events in 2016 and 2017. More mass bleaching occurred this year. “There is no time to lose-we must sharply decrease greenhouse gas emissions ASAP,” the researchers said.

The study, published in the journal Proceedings of the Royal Society B, was conducted by marine scientists at the ARC Centre of Excellence for Coral Reef Studies in Queensland. Scientists assessed the health and size of coral colonies across the reef from 1995 to 2017. They found populations had dropped by more than 50% in all coral sizes and species, but especially in branching and table-shaped corals. These are the large, structural species which usually provide habitats for fish and other marine life.

Prof Terry Hughes, a study co-author, said these coral types had been “worst affected” by the back-to-back mass bleachings which damaged two-thirds of the reef. Bleaching occurs when corals under stress drive out the algae-known as zooxanthellae(虫黄藻)-that give them colour.

Corals can recover if normal conditions return, but it can take decades. A study in 2019 found that damaged coral colonies had struggled to recover because most of the adult corals had died. “A lifeful coral population has millions of small, baby corals, as well as many large ones,” said lead author Dr Andy Dietzel. “Our results show the ability of the Great Barrier Reef to recover its resilience is compromised compared to the past, because there are fewer babies, and fewer large breeding adults.”

Any snakebite can be dangerous if infection sets in. some types of snake poison make the bite area swollen(肿胀的) or painful. Others cause bleeding or damage the heart’s nerves. Here are some especially dangerous snakes:

The largest of all poisonous snakes, king cobras can reach 5.5 meters in length. Each king cobra bits contains enough poison to kill an elephant -- or 20 people. But these big snakes usually avoid people. They live throughout India, southern China and Southeast Asia.

A bite from Australia’s inland taipan, the world’s most poisonous snake, releases enough poison to kill 100 men. The good news is that people rarely come in contact with this snake, and a treatment for its poison exists.

Russell’s viper lives throughout Asia, including India, southern China, and on the island of Taiwan. It prefers grassy fields but can be found in forests and urban areas. It bites more people and causes more deaths than any other poisonous snake.

Though short, the common Indian krait packs a powerful punch(攻击) in its bite. Most often, it strikes people at night while they are sleeping. Since the bite causes little pain, victims are often not sure that they have been bitten until they begin to experience stomach cramps(痉挛). Without treatment, symptoms will worsen quickly and can lead to death.

The black mamba, a native of Africa, is actually olive or grey in color. Only the inside of its mouth is black. When black mambas feel threatened by a human, they make a loud hissing sound to warn the person away. If the warning is ignored, the snake will attack the person repeatedly. And they can attack quickly, moving over the ground at speeds of up to 20 kilometers per hour.

More than 20 years ago, a skeleton called Little Foot turned up in a South African cave. The nearly complete skeleton was a member of the human family. Now researchers have freed most of the skeleton from its stony shell and analyzed the fossils (化石) and they say 3.67-million-years-old Little Foot belonged to a unique species.

Researcher Ronald Clarke and his colleagues think Little Foot belonged to A. Prometheus (普罗米修斯南猿). Clarke works at the university of the Witwatersrand in Johannesburg South Africa. He studies fossilized humans and our relatives. Their foundings, published in four papers, have suggested the species A.Prometheus might have existed. Clarke has believed in that species for more than a decade, he found the first Little Foot’s remains in a storage box of fossils in 1994. People began digging out the rest of the skeleton in 1997.

Many other researchers instead argue that Little Foot likely belonged to a different species, which is known as A.africanus (南方古猿非洲种). Researcher Raymond Dart first identified A.africanus in 1924. He was studying the skull (头颅骨) of an ancient youngster called the Taung Child. Since then, people have turned up hundreds more A. africanus fossils in South African caves. Those include Sterkfontein, where Little Foot was found.

The braincase is the part of the skull that holds the brain. And researchers found a partial braincase that Dart thought belonged to a different species in Makapansgat, one of those other caves. In 1948, Dart called this other species A. Prometheus, but he changed his mind after 1955. Instead, he said that braincase and another fossil at Makapansgat belonged to A.africanus. There was no A. Prometheus after all, he concluded.

Clarke and his colleagues want to bring back the rejected species. They say Little Foot’s distinctive skeleton, an adult female that is at least 90 percent complete, is solid evidence for it.