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On the horizon: News from the frontiers of science.

The whale's tiny ancestor, how global warming may be hurting plants' carbon-fixing ability, and the mystery of Mars's missing limestone

By Peter N. Spotts / January 3, 2008

Jeanette Killius/NEOUCOM/AP

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A whale of a fox tale

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From fox-sized creatures mighty leviathans evolve. That's the story that fossils from India's portion of Kashmir appear to tell about the evolution of whales.

A team led by paleontologist Hans Thewissen says it has found the closest known fossil relative of whales – a four-hoofed creature that had an even number of toes, looked a bit like a miniature deer, and appears to have spent a great deal of time wading in shallow waters some 48 million years ago.

For more than 100 years, scientists have amassed evidence that whales evolved from land mammals. For 15 years, Dr. Thewis­­sen, a professor at Northeastern Ohio Universities Colleges of Medicine and Pharmacy, has uncovered a range of fossils tracing this evolutionary pathway at its geographic center – southern Asia.

The researchers say their find, dubbed Indohyus, shows striking similarities to whales in bone density, structure of ears and early molars, as well as in the oxygen-isotope content of their teeth. The results appeared recently in the journal Nature.

Global warming cools Co2 uptake

Global warming may herald longer growing seasons. But that could undercut the ability of ecosystems to take up heat-trapping carbon dioxide and store it.

That's the word from a team of scientists from Europe, China, Canada, and the United States who studied patterns in the way northern ecosystems around the globe take up and give off CO2. Over the past 20 years' worth of growing seasons, they found that the annual autumn-to-winter build-up of carbon dioxide in the atmosphere is coming earlier than it once did. This apparently is shortening the time each year when plants take up CO2.

They suggest that although plants still take up CO2 via photosynthesis in the fall, that uptake is more than offset by the CO2 plants "exhale" through respiration during that time. This stands in stark contrast to spring activity, when photosynthesis during the growing season takes up more CO2 than respiration gives off. The team calculates that the CO2 emissions from plants in the fall is offsetting roughly 90 percent of the carbon that plants take up in the spring. Currently, Eurasia experiences stronger warming in the spring than in the fall. The opposite is true over North America. Still, overall, autumn warming appears to be outpacing spring warming. If the trend continues, the team says, northern ecosystems may lose their carbon-storage ability faster than previously thought. The results appear in the current edition of the journal Nature.

The mystery of the missing limestone

Planetary scientists have puzzled over an apparent lack of limestone or other carbon-based minerals on Mars. Earth has plenty, testifying to the geologically long-term way Earth stores CO2; it ties it up in rocks. This difference between Earth and Mars has led some to wonder if, early in Martian history, any greenhouse effect the planet's atmosphere had could have been driven by some gas other than CO2.

A team from Harvard University and the Massachusetts Institute of Technology offers a possibility: sulfur dioxide. It's a greenhouse gas, and early in Mars's history, plenty of volcanic activity would have pumped enormous quantities of SO2 into the Martian sky. On Earth, atmospheric oxygen reacts with SO2 to shorten its lifetime in the atmosphere. But on Mars, with far less oxygen, SO2 would stay in the atmosphere longer. And when it did mix with standing water, it would have formed sulfur-based minerals – which NASA's Mars rovers have found in large quantities.

The results appeared in a recent issue of the journal Science.

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