Buzz
On Mars, signs of moisture continue to appear: deeply carved river valleys, extensive deltas, and widespread remnants of evaporating seas have convinced many experts that liquid water may have covered large parts of the Red Planet for a billion years or more. However, most attempts to explain how Martian climate ever allowed such favorable conditions remain unsuccessful.
Today, bitterly cold and arid, Mars required a potent greenhouse atmosphere to maintain its watery past. Initially, a thick layer of heat-trapping carbon dioxide from volcanoes likely enveloped the young planet, but climate simulations repeatedly indicate that CO2 alone could not have kept the surface temperature above freezing.
B.
Now, prompted by the surprising finding that sulfur minerals are widespread in Martian soil, scientists are beginning to suspect that CO2 had a warming companion: sulfur dioxide (SO2). Similar to CO2, SO2 is a common gas released during volcanic eruptions, which were frequent on early Mars. Even a fraction of a percent of SO2 in Mars's early atmosphere could have provided the additional greenhouse warming that the Red Planet needed to sustain its wet conditions, explains geochemist Daniel P. Schrag of Harvard University.
C.
That might not seem like much, but for many gases, even tiny concentrations are difficult to maintain. On our home planet, SO2 doesn't provide significant long-term warmth because it quickly combines with oxygen in the atmosphere to form sulfate, a type of salt. Early Mars would have had almost no atmospheric oxygen, so SO2 would have persisted much longer.
D.
“Removing oxygen causes a profound change, and the atmosphere behaves very differently,” remarks Schrag. According to Schrag and his team, this difference also suggests that SO2 would have played a major role in the Martian water cycle, thereby solving another climate puzzle: the absence of certain types of rocks.
E.
Schrag's group argues that on early Mars, much of the SO2 would have reacted with airborne water droplets and precipitated as sulfurous acid rain, instead of forming salts like on Earth. The resulting acidity would have hindered the formation of thick layers of limestone and other carbonate rocks. Scientists had anticipated Mars to be rich in carbonate rocks due to their formation in a humid, CO2-rich atmosphere.
Over millions of years, this rock-forming process has trapped enough carbon dioxide emitted by Earth's volcanoes to limit its accumulation in the atmosphere. Disrupting this CO2-sequestration process on early Mars would have caused more of the gas to build up in the atmosphere—another way SO2 could have enhanced greenhouse warming, suggests Schrag.
F.
Some scientists question whether SO2 could really have performed these climate-related roles. Even in an oxygen-free atmosphere, SO2 is quite fragile; the sun's ultraviolet radiation readily breaks apart SO2 molecules, notes James F. Kasting, an atmospheric chemist at Pennsylvania State University.
In Easting’s computer models of Earth’s early climate, often compared with that of early Mars, this photochemical breakdown limited SO2 concentrations to one thousandth of what Schrag and his colleagues describe. “There may be ways to make this concept work,” Kasting remarks. “But it would require detailed modeling to convince skeptics, including myself, of its feasibility.”
G.
Schrag acknowledges the uncertainties, but he cites estimates from other researchers suggesting that early Martian volcanoes might have emitted enough SO2 to offset the photochemical destruction. Previous studies also indicate that a thick CO2 atmosphere would have effectively scattered the most harmful UV wavelengths—a further example of a potentially beneficial partnership between CO2 and SO2 on early Mars.
H.
Kasting argues that an SO2 climate feedback alone couldn't have warmed early Mars to Earth-like temperatures, but he acknowledges the possibility that SO2 levels could have remained high enough to prevent complete freezing, potentially allowing for rainfall and the formation of river valleys. Schrag agrees on this point. “Our hypothesis doesn’t hinge on whether there was a large ocean, a few lakes, or just small puddles,” he says. “'Warm' doesn’t mean 'Amazon warm.' It could mean 'Iceland warm'—just enough to create those river valleys.”
If sulfur dioxide indeed warmed early Mars, as a new theory suggests, it would have led to the formation of sulfite minerals in surface water. No sulfites have been discovered so far, possibly because they haven’t been actively sought. The next-generation Mars rover, the Mars Science Laboratory, equipped with an x-ray diffractometer for identifying mineral crystal structures, is poised to search for them.
Questions 1-6
The passage consists of seven paragraphs labeled A-H.
Which paragraph contains the information described below? Write the appropriate letter A-H in boxes 1-6 on your answer sheet.
NB You may use any letter more than once.
1. A problem indirectly solved by SO2.
2. A device with an astounding ability for detection.
3. A potential contributor to the warmth of the Mars interacting with CO2.
4. The destructive effect brought by the sunlight proposed by the opponents.
5. A specific condition on early Mars to guarantee the SO2 to maintain in the atmosphere for a long time.
6. Conflicting climatic phenomena co-existing on the Mars.
Questions 7-9
Are the following statements consistent with the information provided in the Reading Passage? Write your answers in boxes 7-9 on your answer sheet.
| TRUE | If the statement is true |
| FALSE | If the statement is false |
| NOT GIVEN | If the information is not given in the passage |
7. Schrag has provided concrete proofs to fight against the skeptics for his view.
8. More and more evidences show up to be in favor of the leading role SO2 has for the warming up the Mars.
9. The sulfites have not been detected probably because of no concern for them.
Questions 10-13
Complete the following summary of the paragraphs of Reading Passage, using No More than Three words from the Reading Passage for each answer. Write your answers in boxes 10-13 on your answer sheet.
Summary:
An opinion held by Schrag’s team indicates that 10… formed from the integration of SO2 with 11… would have stopped the built up of thick layers of limestone as well as certain carbonate rocks. Wetness and abundance in CO2 could directly result in the good production rocky layer of 12… . As time went by, sufficient CO2 was emitted from the volcanoes and restricted the formation of the gas in the afr. To stop this process made SO2 possible to accelerate 13 …
Response:- D (Đoạn D, “…that difference also implies that S02 would have played a starring role in the Martian water cycle—thus resolving another climate conundrum, namely, a lack of certain rocks.)
- H (Đoạn H, “If sulfur dioxide warmed early Mars, as a new hypothesis suggests, minerals called sulfites would have formed in standing water at the surface.”)
- B (Đoạn B, “Now, inspired by the surprising discovery that sulfur minerals are pervasive in the Martian soil, scientists are beginning to suspect that C02 had a warm-up partner: sulfur dioxide (S02)”).
- F (Đoạn F, “…The sun’s ultraviolet radiation splits apart S02 molecules quite readily, points out James F. Kasting, an atmospheric chemist at Pennsylvania state University.”)
- C (Đoạn C, “Early Mars would have been virtually free of atmospheric oxygen, though, so S02 would have stuck around much longer.”)
- A (Đoạn A, “On Mars, signs of wetness keep pouring in: deeply carved river valleys, vast deltas and widespread remnants of evaporating seas have convinced many experts that…”)
- FALSE (Đoạn G, “Schrag admits that the details are uncertain, but he cites estimates by other researchers who suggest that…”)
- NOT GIVEN (Không có thông tin)
- TRUE (Đoạn H, “No sulfites have yet turned up, possibly because no one was looking for them.”)
- Sulfurous acid rain (Đoạn E, “Schrag’s team contends that on early Mars, much of the S02 would have combined with airborne water droplets and fallen as sulfurous acid rain…”)
- Airborne water droplets (Đoạn E, “Schrag’s team contends that on early Mars, much of the S02 would have combined with airborne water droplets and fallen as sulfurous acid rain…”)
- Limestone and carbonate (Đoạn E, “ The resulting acidity would have inhibited the formation of thick layers of limestone and other carbonate rocks.”)
- Greenhouse warming (Đoạn E, “…another way S02 could have boosted greenhouse warming, Schrag suggests.”)
