Last Week's Top Ten Science Stories, 21-27 August

Astronomers find the best evidence yet that dark matter really exists, geologists spark a new mystery about the formation of atmospheric oxygen, and psychologists show that we judge the trustworthiness of a person incredibly fast. And, yes, Pluto is no longer a planet.

10. Ocean Noise Has Increased Considerably since 1960s

With populations increasing around the globe in recent decades, no one would be surprised by an increase in the amount of noise produced in terrestrial environments. Now, a unique study has shown that the underwater world also is becoming a noisier place, with unknown effects on marine life.

The study showed that noise levels in 2003-2004 were 10 to 12 decibels higher than in 1964-1966, an average noise increase rate of three decibels per decade. The culprit behind the increase appears to be a byproduct of the vast increase in the global shipping trade, the number of ships plying the world's oceans and the higher speeds and propulsion power for individual ships.

"We've demonstrated that the ocean is a lot noisier now than it was 40 years ago. The noise is more powerful by a factor of 10," said John Hildebrand, a professor of oceanography in the Marine Physical Laboratory at Scripps.

9. No Hobbits in this Shire

In 2004 scientists discovered in a cave on the island of Flores, Indonesia, the skeletal remains of what was thought to be a new human species. But a study now reveals that in fact they are the ancestors of modern human pygmies who live on the island today.

The researchers also demonstrate that the fairly complete skeleton designated LB1 is microcephalic, while other remains excavated from the site share LB1's small stature but show no evidence of microcephaly, since no other brain cases are known. Microcephaly is a condition in which the head and brain are much smaller than average for the person's age and gender. It can be present at birth or develop afterwards and is associated with a complex of other growth and skeletal anomalies.

8. Use of Stone Hammers Sheds Light on Geographic Patterns of Chimpanzee Tool Use

Until recently it was thought that chimpanzee nut-cracking behavior was confined to the region west of the N'Zo-Sassandra River in Cote d'Ivoire. Because there are no relevant ecological or genetic differences between populations on either side of this "information barrier," the implication had been that nut-cracking is a behavioral tradition constrained in its spread by a physical barrier: It was absent to the east of the river because it had not been invented there.

However, scientists have now found that chimpanzees crack open nuts more than 1700 km east of the supposed barrier. According to the authors of the study, the discontinuous distribution of the nut-cracking behavior may indicate that the original "culture zone" was larger, and nut-cracking behavior has become extinct between the N'Zo-Sassandra and Ebo. Alternatively, it may indicate that nut-cracking has been invented on more than one occasion in widely separated populations.

7. New Definition of Species

The classical definition of species was proposed by Ernst Mayr in 1942, defining it as reproductively isolated groups of organisms. However, it is hard to observe mating and to know whether there is interbreeding between populations and thus creation of hybrid species. This is why traditionally, species have been recognized based on physical characteristics, although it has been assumed that species differences are inherited and thereby reflect genetic differences.

Researchers Robert Baker and Robert Bradley have now defined "species" based on genetic data. The new definition distinguishes species that are genetically isolated from one another. This new definition leads to an easier identification of species but there also seem to be many more species than previously thought present.

Baker and Bradley's genetic species concept also differs from the phylogenetic species concept proposed by Joel Cracraft in 1989 by emphasizing genetic isolation and protection of the integrity of the gene pool.

6. How an Important Biological Function Can Be Lost

Piglets are sensitive to cold and shiver to maintain their body heat. Researchers at Uppsala University have uncovered a genetic reason why these newborns are less tolerant of the cold than other newborn mammals. It turns out that the gene that codes for the protein UCP1 was inactivated some 20 million years ago in the evolutionary line to which pigs belong. Thus, this ancestor of pigs lost the ability to use brown fat to maintain body temperature after birth.

A reasonable explanation for this is that brown fat was not essential during a period in the evolution of pigs, in which they lived in a warm climate. The ancestor of the domesticated pig, the wild boar, is the only pig that lives in cold climates, all other species inhabiting tropical or subtropical climates. The wild boar has compensated for the loss of brown fat by a series of adaptations for survival in a cold climate. It is the only hoofed animal that builds a den when it is time to give birth, and its young shudder to maintain their body temperature. In modern pig production, heat lamps are used to help the newborn piglets retain their body temperature.

5. NASA Finds Direct Proof of Dark Matter

Astronomers used NASA's Chandra X-ray Observatory, the Hubble Space Telescope, the European Southern Observatory's Very Large Telescope and the Magellan optical telescopes to observe the high-speed collision of a smaller galaxy cluster with a larger one. They were interested in observing the gravitational effects during this collision.

The observations provide the strongest evidence yet that most of the matter in the universe is dark. Despite considerable evidence for dark matter, some scientists have proposed alternative theories for gravity where it is stronger on intergalactic scales than predicted by Newton and Einstein, removing the need for dark matter. However, such theories cannot explain the observed effects of this collision.

"A universe that's dominated by dark stuff seems preposterous, so we wanted to test whether there were any basic flaws in our thinking," said Doug Clowe of the University of Arizona at Tucson, and leader of the study. "These results are direct proof that dark matter exists."

4. Sulfur Signature Changes Thoughts on Atmospheric Oxygen

Ancient sediments that once resided on a lake bed and the ocean floor show sulfur isotope ratios unlike those found in other samples from the same time, calling into question accepted ideas about when the Earth's atmosphere began to contain oxygen, and thus when did life appeared.

"The popular model is that there was little oxygen in the Earth's atmosphere before about 2.4 billion years ago," says Dr. Hiroshi Ohmoto, professor of geochemistry and director, Penn State Astrobiology Research Center. "Scientists use the ratio of the various sulfur isotopes as their strongest evidence for atmospheric oxygen."

One possible explanation of this abnormal sulfur isotope ratio is that perhaps oxygen levels during that time period fluctuated greatly creating a "yo yo" atmosphere: Going from oxygenless before 3 billion years ago to oxygenated between 3 billion and 2.75 billion years ago and then back to oxygenless from 2.75 billion to 2.4 billion years ago.

Another explanation could be that the atmosphere contained oxygen as early as 3.8 billion years ago. This would mean that life appeared on Earth very early.

3. Incredibly Snap Judgments Decide a Face's Character

We may be taught not to judge a book by its cover, but when we see a new face, our brains decide whether a person is attractive and trustworthy within a tenth of a second. People respond intuitively to faces so rapidly that our reasoning minds may not have time to influence the reaction -- and that our intuitions about attraction and trust are among those we form the fastest.

Why the brain makes such snap judgments is not yet entirely clear. However, brain scans suggest that the part of the brain that responds directly to fear may be involved in judgments of trustworthiness.

"The fear response involves the amygdala, a part of the brain that existed in animals for millions of years before the development of the prefrontal cortex, where rational thoughts come from," Princeton University psychologist Alex Todorov explained. "We imagine trust to be a rather sophisticated response, but our observations indicate that trust might be a case of a high-level judgment being made by a low-level brain structure. Perhaps the signal bypasses the cortex altogether."

2. Pluto Downgraded to 'Dwarf Planet' Status

This was a sad week for Pluto. After 75 years of being the ninth planet, the International Astronomical Union (IAU) downgraded its status to that of a "dwarf planet". IAU decided that in order for a body to be called a planet it has to be round, revolve around the Sun and clear the space around it.

Pluto is part of the Kuiper Belt, a zone in the outer solar system, beyond Neptune, containing numerous bodies, some very small and some even larger than Pluto, such as "Xena". Astronomers expect to find many more fairly large Kuiper Belt objects.

The large and round asteroid Ceres that exists between Mars and Jupiter, retained is asteroid status because it is also part of a larger group of numerous asteroids.

Thus the planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

1. What Happened in the Aftermath of the Dinosaur Extinction?

When the Earth was struck by an asteroid 65 million years ago a mass extinction followed. Dinosaurs were part of that mass extinction. But how did nature get over that horrific event? How did biodiversity recover?

"We know that right after the extinction, for 800,000 years, there was very low insect predation and plant diversity. We know that 9 million years afterwards, there was renewed diversity in both plants and insects." What happened in the 8 million years in between?

The extinction destroyed the ecological links in the food web. Plants and insects were killed outright, and herbivorous insects took a further hit when the plants they were specialized to eat disappeared. Surviving insects faced the choice of shifting their food resource or dying. Many died, but in most places a few survived, and from these, some evolved to feed on new host plants.

As the ecosystem rebuilt new links from its shattered state, the empty ecological space was open to opportunism, and in a few places the food chain became unbalanced and unstable.

"In modern forests, insect diversity tracks plant populations. If there are few plants, there are few insects, and that is what we expected to see and mostly found throughout the 10-million-year Paleocene. However, we looked extremely hard to test this conventional wisdom and found some shocking exceptions that have given us new ideas about how food webs recover from mass extinction".