Rain on the Martian Plain?



Picture of channels

Before the rains came. Martian water may have carved out channels like these early in its history, but eventually the torrents were replaced by light rain.

Martian soil data collected by five robotic missions indicates that rain fell on the Red Planet billions of years ago. The findings provide no new insight into the possibility of martian life, but they do suggest that further clues to Mars’s past could be found right here on Earth.

There’s little doubt now that Mars once was wet. The twin Mars Exploration rovers–Spirit and Opportunity–have been finding signs of water-associated minerals for 4 years now. And less than 2 weeks ago, the Phoenix Mars Lander struck water ice while digging at the north polar region (ScienceNOW, 20 June). What remains to be determined is where this wetness came from and how long it lasted. Preliminary investigations by Mars mission scientists, as well as high-resolution images taken by orbiters, have suggested that water on Mars surged up from deep below the surface, sometimes carving extensive channels and gullies (see photo).

Now, a team led by geologist Ronald Amundson of the University of California, Berkeley, has found indications of rain by studying our own planet’s geochemistry. Analyzing soil samples collected by five previous missions, including the 1976 Viking and 1997 Pathfinder landers, the researchers found a distinctive pattern of chloride and sulfate deposits. In all of the samples, the data show that the sulfates tend to stay nearer to the surface, whereas chloride concentrations increase with depth. That’s the same pattern found in extremely arid places on Earth such as Antarctica’s dry-valley regions and Chile’s Atacama Desert. In these areas, rain is light and infrequent, but over millions of years it can change the chemical makeup of soil by depositing sulfates near the surface and by transporting the more soluble chlorides farther into the soil.

So the picture emerging is that by about 3 billion years ago, the biggest bodies of water on the martian surface, which were derived from groundwater, had mostly frozen or evaporated, the researchers report online this month in Geochimica et Cosmochimica Acta. Then a prolonged period of intermittent drizzle and dew began. That climate apparently continued long enough to alter the chemistry of surface minerals, creating the pattern detected by the analyses.

It’s a convincing argument, says planetary scientist Itay Halevy of Harvard University: "Atmospherically delivered water and downward migration of salts, both common processes on Earth, played a part in the formation of martian soils, too." Moreover, the results "provide further chemical support for what previous studies have found: that during early parts of Mars’s history, liquid water existed on the surface for geologically significant periods of time."

Pollutants in the deep-ocean food web

Scientists say the concentrations of pollutants they documented in deep-sea squid are surprising?

Research published online May 22 in Marine Pollution Bulletin presents new evidence that human-made contaminants are finding their way into the deepest parts of the ocean. The paper is one of the first reports of persistent organic pollutant uptake by deep-sea mollusks, an important part of the marine food chain.

This deep-sea mollusk, <em>Histioteuthis reversa</em>, is called the jewel squid because of its many photophores, or light-producing organs, which appear as dark dots on its skin.

This deep-sea mollusk, Histioteuthis reversa, is called the jewel squid because of its many photophores, or light-producing organs, which appear as dark dots on its skin.

A team of researchers from the Virginia Institute of Marine Science and the National Marine Fisheries Service (NMFS) collected nine species of cephalopods, a class of organisms that includes octopods, squids, cuttlefish, and nautiluses, from depths between 1000 and 2000 meters (about 3300 to 6600 feet) in 2003 in the western North Atlantic Ocean. The team selected species for chemical analysis on the basis of their importance as prey and analyzed specimens for 11 classes of anthropogenic chemical contaminants. The compounds the researchers detected include DDT, PAHs, PCBs, PBDEs, tributyltin, and toxaphene.

“It was surprising to find measurable and sometimes high amounts of toxic pollutants in such a deep and remote environment,” says coauthor Michael Vecchione of NMFS.

Although scientists have previously looked for persistent organic pollutants in deep-sea fish, there is little information on such chemicals in deep-sea cephalopods. The large variety of contaminants that the scientists reported in the new paper makes it “apparent that contamination of the deep-sea oceanic food web is occurring,” they write.

“The cephalopod species we analyzed span a wide range of sizes and represent an important component of the oceanic food web,” Vecchione says. He explains that he and his colleagues initiated the study in response to recent reports documenting the accumulation of persistent organic pollutants in the blubber and tissues of whales and other predatory marine mammals as well as in some deep-sea fish. The researchers set out to determine whether whales have a unique capacity to accumulate pollutants or are simply one of the top predators in a contaminated deep-sea food web. The finding that cephalopod tissues contained some of the same compounds that have been reported to bioaccumulate in marine mammals points to the latter hypothesis.

“Contamination of the deep-sea food web is happening, and it is a real concern,” Vecchione concludes.



  • Antarctic iceCrash! In one doomsday scenario, global warming triggers titanic chunks of ice to break and slide off the Antarctic landmass, causing sea levels to rise by meters. The surrounding Antarctic ice shelf has been splitting over the past 2 decades–but is this a harbinger of doom or just part of some natural cycle? Researchers using underwater acoustic sensors originally designed to detect nuclear explosions have listened to the grinding and cracking of the ice, and they have now determined that–at least over the past 7 years–there has been no increase in Antarctic ice shelf break-up. The results, reported this week at the Acoustics 2008 meeting in Paris, France, provide a baseline for the rate of Antarctic splitting. The question now is whether it will increase as the temperature rises.




* 水处理技术开发及工程设计(给排水乙级资质)

* 环境规划与影响评价(环境影响评价甲级资质);

* 水资源论证(水文、水资源调查评价甲级资质);

* 污染环境修复以及资源综合利用;

* 清洁生产与风险评价;

* 环境质量监测、检测;

* 环境保护科技咨询;

* 环境保护相关领域专业翻译;

* 环境保护教育与培训。


古力特心中历史最佳11人:超级锋线 球王非他莫属


  新浪体育讯 足坛巨星古力特接受英国《442》杂志邀请,评出了自己心中的历史最佳11人阵容。