Old Fossils
Scientists have found what they think is probably the oldest fossil on Earth, a remnant of life from 3.7 billion years ago when Earth's skies were orange and its oceans green.
In a newly melted part of Greenland, Australian scientists found the leftover structure from a community of microbes(微生物) that lived on an ancient seafloor.Based on their analysis of the fossils, the researchers determined that they are 220 million years older than those discovered in Western Australia, which were 3.48 billion years old.
The discovery shows life may have formed quicker and more easily than once thought, about half a billion years after Earth formed.And that may also give hope for life forming elsewhere, such as Mars, said study co-author Martin VanKranendonk of the University of New South Wales and director of the Australian Center for Astrobiology.“It gives us an idea how our planet evolved and how life gained_a_foothold，” VanKranendonk said.
Scientists had thought it would take at least half a billion years for life to form after the molten Earth started to cool a bit, but this shows it could have happened quicker, he said.That's because the newly found fossil is far too complex to have developed soon after the planet's first life forms, he said.
In an outcrop of rocks that used to be covered with ice and snow which melted after an exceptionally warm spring, the Australian team found stromatolites(叠层石), which are layered structures that are often produced by a community of microbes.The stromatolites were about 1 to 4 centimeters high.
“It is like the house left behind made by the microbes，” VanKranendonk said.“Scientists used the layers of ash from volcanoes and tiny zircon(锆石) with uranium and estimated that they date back to 3.7 billion years ago.”
The dating seems about right, said Abigail Allwood, a NASA astrobiologist who found the previous oldest fossil, from 3.48 billion years ago, in Australia.But Allwood said she is not completely convinced that what VanKranendonk's team found once was alive.She said the evidence wasn't conclusive enough that it was life and not a geologic quirk(地质巧合)．“It would be nice to have more evidence, but in these rocks that's a lot to ask，” Allwood said in an email.
1. The underlined words “gained a foothold” in Paragraph 3 mean.| A．continued | B．changed |
| C．increased | D．started |
| A．the fossil appeared soon after the birth of the earth |
| B．the fossil formed soon after the earth's first life |
| C．life formed earlier than the newly found fossil |
| D．life appeared about half a billion years ago |
| A．Neutral. | B．Sceptical. |
| C．Objective. | D．Supportive. |
| A．the previous fossils are a geologic quirk |
| B．the previous fossils are made up of stromatolites |
| C．the newly found fossils come from Western Australia |
| D．the newly found fossils have a history of 3.7 billion years |
相似题推荐
【推荐1】City trees grow faster and die younger than trees in rural forests, a new study finds.
Studies had shown forests take in greenhouse gas. But there hadn’t been much data on whether city trees grow, die and take in CO2 at the same rate as forest trees do. So Lucy Hytyra and her workmates at Boston University in Massachusetts decided to find out.
To figure out how quickly trees were growing, the researchers tracked their diameters (直径) between 2005 and 2014. The team focused on red oaks and red maples growing on Boston streets. These trees grew four times faster than the same species did in a nearby forests. Faster-growing trees take in more CO2. Over the nine years, the researchers tracked these trees, and they found city ones took in four times as much CO2 from the air as the forest trees did. The city trees also, however, were twice as likely to die. So over the lifetime of each type of tree, forest trees actually take in more CO2.
“City trees grow faster mainly because they have less competition for light from their neighbors,” Hutyra says. In a forests, trees tend to grow close together, shading their neighbors. Street trees also benefit from higher levels of nitrogen (氮) in rainwater. Nitrogen is an element that helps plants grow. Still, she says that her team’s findings may not apply to arid cities. “In locations short of water like Phoenix or Los Angeles, city trees might respond differently because it’s very hot in the city and they have so little water.” At such sites, she says, “Trees might grow slower.”
So why were Boston’s streets trees twice as likely as their country cousins to die young? City roads can leave big-tree roots less room to grow. Plus, people often decide to cut down trees that are sick, or in the way of some desired building or view.
1. What can we learn from the research by Lucy’s team?| A．City trees live twice longer than forest trees. |
| B．Over their lifetime, forest trees actually take in more CO2. |
| C．Over the nine years, faster-growing trees breathe in less CO2. |
| D．On Boston streets red oaks grow much faster and taller than red maples. |
| A．they live in hot weather | B．they take in more water |
| C．they tend to grow close together | D．they benefit from more light and nitrogen |
| A．Dry. | B．Busy. | C．Crowded. | D．Large. |
| A．The result of people’s behavior. |
| B．The relationship between people and trees. |
| C．The fact that the roots of city trees have more room. |
| D．The reasons why the street trees in Boston died young. |
| A．A travel journal. | B．A story book. | C．A science magazine. | D．A medical report |
【推荐2】People have wondered for a long time how their personalities and behaviors are formed. It’s not easy to explain why one person is intelligent and another is not, or why one is cooperative and another is competitive.
Social scientists are, of course, extremely interested in these types of questions. They want to explain why we possess certain characteristics and exhibit certain behaviors. There are no clear answers yet, but two distinct schools of thought on the matter have developed. As one might expect the two approaches are very different from one another, and there is a great deal of debate between proponents of each theory. The controversy is often (conveniently) referred to as “nature/nurture”.
Those who support the “nature” side of the conflict believe that our personalities and behavior patterns are largely determined by biological and genetic factors. That our environment has little, if anything, to do with our abilities, characteristics, and behavior is central to this theory. Taken to an extreme, this theory maintains that our behavior is predetermined to such a great degree that we are almost completely governed by our Instincts.
Proponents of the “nurture” theory, or, as they are often called behaviorists, claim that our environment is more important than our biologically based instincts in determining how we will act. Behaviorists see humans as being whose behavior is almost completely shaped by their surroundings. Their view of the human being is quite mechanistic; they maintain that like machines, humans respond to environmental stimuli as the basis of their behavior.
The social and political implications of these two theories are profound. In the United States, for example, blacks often score below whites on standardized intelligence test. This leads some “nature” proponents to conclude that blacks are genetically inferior to whites. Behaviorists, in contrast, say that the differences in scores are due to the fact that blacks are often deprived of many of the educational and other environmental advantages that white enjoy, and that, as a result, they do not develop the same responses that whites do.
Neither of these theories can yet fully explain human behavior. In fact, it is quite likely that the key to our behavior lies somewhere between these two extremes. That the controversy will continue for a long time is certain.
1. The author is mainly concerned about solving the problem ________.| A．why one’s behaviors differ from others’ |
| B．what makes different stages of intelligence |
| C．how social scientists form different theories |
| D．what causes the “nature/nurture” controversy |
| A．approaches | B．advocates | C．principles | D．characters |
| A．They believe human beings are mechanical. |
| B．They compare our behaviors to the machines. |
| C．They suggest that we react to the environment as the machines do. |
| D．They uphold that the mechanistic theory can be applied on us as well. |
| A．are the result of the educational disadvantages |
| B．have nothing to do with their true intelligence |
| C．are an indication of the blacks’ poor intelligence |
| D．have nothing to do with factors other than instincts |
Most people, when they travel to space, would like to stay in orbit for a few days or more. And this stands to reason, if you’re paying $20,000 for your trip to orbit. So in order for tourism to reach its full potential there’s going to be a need for orbital accommodation - or space hotels.
The hotels themselves will vary greatly - from being quite simple in the early days to huge luxury structure at a later date. It’s actually surprising that as late as 1997, very few designs for space hotels were published.
Lots of people who’ve been to space have described vividly what it’s like to live in zero gravity.
| A．What would a space hotel actually be like? |
| B．The Zero-G Corporation was founded by Peter Diamandis, offering chances to experience what it feels like to be in an environment of true weightlessness. |
| C．Would it be amazingly expensive to carry out the plan? |
| D．Of course all good things have come to an end, unfortunately. |
| E．There are obviously all sorts of possibilities for dancing, gymnastics, and zero-G sports. |
| F．This is mainly because those who might be expected to design them, haven’t expected launch costs to come down far enough to make them possible. |
