Moon may be younger than thought, study says

An analysis of a lunar rock raises questions about when and how the moon was formed. It may be 200 million years younger than widely believed.

The moon rises over Los Angeles City Hall. The new analysis could leave scientists who model the moon's formation "scratching their heads," said an isotope geochemist who was not involved in the study. (Scott Harrison / Los Angeles Times)

By Amina Khan, Los Angeles Times

The moon may be 200 million years younger than widely believed, according to a new analysis of a rock brought back to Earth in 1972 by Apollo 16 astronauts. Or, if not, the moon may never have had the magma ocean that scientists think covered its surface soon after it formed.

Either way, the findings published online Wednesday by the journal Nature could send lunar scientists back to the drawing board to reconsider the moon's evolution.

The moon is thought to have formed from debris ejected into space after a Mars-sized body collided with the still-molten Earth about 4.5 billion years ago. The young moon would have been hot and blanketed by magma. But without a thick atmosphere to trap its heat, the molten rock cooled relatively quickly, while minerals that were less dense than the magma floated to the top first, forming the moon's crust. These rocks give the white highlands of the moon's near side their pale hue, and have been used to determine the point at which the moon solidified into the body we know today.

But an international team of scientists decided to use sophisticated techniques to better test a sample collected by the Apollo 16 mission — one that was considered one of the oldest moon rocks and that would, with any luck, provide an accurate age because it is relatively unscathed by meteoric impacts.

Planetary scientists can determine a rock's age by calculating how many radioactive "parent" isotopes of a particular element have decayed into "daughter" isotopes. But rather than test the radioactive decay using just one method, the researchers used three, involving the elements lead, samarium and neodymium. Because different isotopes decay at different rates, each method provided a slightly different measuring stick.

All three calculations resulted in very similar ages: an average of about 4.36 billion years, which surprised the scientists. "We all looked at one another and laughed," said lead author Lars Borg, a geochemist at Lawrence Livermore National Laboratory in Northern California.

If that is correct, it means the moon's magma ocean formed — and cooled — more recently than scientists have generally thought was the case based on evidence from meteorites containing some of the oldest minerals in the solar system. This also could mean that the great impact that separated the moon from Earth happened more recently too.

The study authors propose another, more radical, explanation: The crustal rock they analyzed, called ferroan anorthosite, is not linked to magma dynamics at all. Perhaps the moon never even had a magma ocean and the rocks were formed another way, they suggested.

"You're left with picking your poison," Borg said.

The new dates could leave scientists who model the moon's formation "scratching their heads," said Alex Halliday, an isotope geochemist at Oxford University who was not involved in the study. "It's a little bit awkward, because nobody likes to say, 'They've got their data wrong.' "

But there are less dramatic explanations, Halliday said, including the possibility that both these and previous dates are right, and the ferroan anorthosite examined in this study simply does not represent the oldest rocks on the lunar surface.

"I hope it's going to cause a real stir," said Clive Neal, a planetary geologist at the University of Notre Dame who was not involved in the study. But, he added, the researchers need much more evidence that other rocks have been inaccurately dated before they jump to radically different theories about the moon's formation.

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Potato genome sequenced by international team

The humble spud provides the world's fourth-largest crop

An international team has uncovered the full DNA sequence of the potato for the first time.

The breakthrough holds out the promise of boosting harvests of one of the world's most important staple crops.

Researchers at the James Hutton Institute in Dundee, which contributed to the work, say it should soon be possible to develop improved varieties of potato much more quickly.

The genome of an organism is a map of how all of its genes are put together.

Each gene controls different aspects of how the organism grows and develops.

Slight changes in these instructions give rise to different varieties.

Each individual has a slightly different version of the DNA sequence for the species.

Professor Iain Gordon, chief executive of the James Hutton Institute, said decoding the potato genome should enable breeders to create varieties which are more nutritious, as well as resistant to pests and diseases.

Colour and flavour

He hopes it will help meet the challenge of feeding the world's soaring population.

The research is far from complete. Analysing the genetic sequence of the plant will take several more years.

At the moment it can take more than 10 years to breed an improved variety.

By locating the genes that control traits like yield, colour, starchiness and flavour, the research should make it possible to develop better spuds much more quickly.

Potatoes provide the world's fourth-largest crop, with an annual, global yield of 330m tonnes.

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Ocean's carbon dioxide uptake reduced by climate change

How deep is the ocean's capacity to buffer against climate change? As one of the planet's largest single carbon absorbers, the ocean takes up roughly one-third of all human carbon emissions, reducing atmospheric carbon dioxide and its associated global changes.

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But whether the ocean can continue mopping up human-produced carbon at the same rate is still up in the air. Previous studies on the topic have yielded conflicting results, says University of Wisconsin-Madison assistant professor Galen McKinley.

In a new analysis published online July 10 in Nature Geoscience, McKinley and her colleagues identify a likely source of many of those inconsistencies and provide some of the first observational evidence that climate change is negatively impacting the ocean carbon sink.

"The ocean is taking up less carbon because of the warming caused by the carbon in the atmosphere," says McKinley, an assistant professor of atmospheric and oceanic sciences and a member of the Center for Climatic Research in the Nelson Institute for Environmental Studies.

The analysis differs from previous studies in its scope across both time and space. One of the biggest challenges in asking how climate is affecting the ocean is simply a lack of data, McKinley says, with available information clustered along shipping lanes and other areas where scientists can take advantage of existing boat traffic. With a dearth of other sampling sites, many studies have simply extrapolated trends from limited areas to broader swaths of the ocean.

McKinley and colleagues at UW-Madison, the Lamont-Doherty Earth Observatory at Columbia University, and the Universite Pierre et Marie Curie in Paris expanded their analysis by combining existing data from a range of years (1981-2009), methodologies, and locations spanning most of the North Atlantic into a single time series for each of three large regions called gyres, defined by distinct physical and biological characteristics.

They found a high degree of natural variability that often masked longer-term patterns of change and could explain why previous conclusions have disagreed. They discovered that apparent trends in ocean carbon uptake are highly dependent on exactly when and where you look – on the 10- to 15-year time scale, even overlapping time intervals sometimes suggested opposite effects.

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"Because the ocean is so variable, we need at least 25 years' worth of data to really see the effect of carbon accumulation in the atmosphere," she says. "This is a big issue in many branches of climate science – what is natural variability, and what is climate change?"

Working with nearly three decades of data, the researchers were able to cut through the variability and identify underlying trends in the surface CO2 throughout the North Atlantic.

During the past three decades, increases in atmospheric carbon dioxide have largely been matched by corresponding increases in dissolved carbon dioxide in the seawater. The gases equilibrate across the air-water interface, influenced by how much carbon is in the atmosphere and the ocean and how much carbon dioxide the water is able to hold as determined by its water chemistry.

But the researchers found that rising temperatures are slowing the carbon absorption across a large portion of the subtropical North Atlantic. Warmer water cannot hold as much carbon dioxide, so the ocean's carbon capacity is decreasing as it warms.

In watching for effects of increasing atmospheric carbon on the ocean's uptake, many people have looked for indications that the carbon content of the ocean is rising faster than that of the atmosphere, McKinley says. However, their new results show that the ocean sink could be weakening even without that visible sign.

"More likely what we're going to see is that the ocean will keep its equilibration but it doesn't have to take up as much carbon to do it because it's getting warmer at the same time," she says. "We are already seeing this in the North Atlantic subtropical gyre, and this is some of the first evidence for climate damping the ocean's ability to take up carbon from the atmosphere."

She stresses the need to improve available datasets and expand this type of analysis to other oceans, which are relatively less-studied than the North Atlantic, to continue to refine carbon uptake trends in different ocean regions. This information will be critical for decision-making, since any decrease in ocean uptake may require greater human efforts to control carbon dioxide levels in the atmosphere.

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