Feature Earth

Earth: Science news of the year, 2008

Science News writers and editors looked back at the past year's stories and selected a handful as the year's most interesting and important in Earth. Follow hotlinks to the full, original stories.

By Science News

December 19, 2008 at 7:16 pm

Rocks in the Jack Hills of Western Australia hosted zircon crystals that contain tiny mineral inclusions, such as the one denoted by the arrow in the false-color inset. The zircons and inclusions are more than 4 billion years old and contain evidence suggesting an early start for tectonic activity on Earth.

Evidence included
Zircons hint at early tectonic activity, life

Two analyses of tiny mineral bits that crystallized during the Earth’s formative years have provided new insights into the planet’s earliest days.
One study of mineral inclusions in zircons from the Jack Hills of Western Australia hints that the crystals formed at depths of around 25 kilometers and at temperatures of about 700° Celsius. Those findings, in turn, suggest that plate tectonics had already begun on Earth between 4.19 billion and 4.02 billion years ago, less than 600 million years after the planet first coalesced (SN: 1/3/09, p. 10).

Another study, this one of the carbon-isotope ratios of microdiamond inclusions in zircons that ranged between 3.05 billion and 4.25 billion years of age, found a much-lower-than-average concentration of the carbon-13 isotope in those inclusions, a possible sign of biological processes (SN: 8/2/08, p. 13). Metabolic processes that take place in an organism’s cells, and especially in microorganisms, produce isotopically light carbon. A much-higher-than-average concentration of carbon-12, the lightest of carbon’s stable isotopes, often is a sign that the carbon was generated by biologic activity.

The ratio of carbon-13 to carbon-12 was far below that found in other diamonds and even in other reservoirs of isotopically light carbon, including carbon-rich meteorites and interplanetary dust. If the ratio is indeed a sign of life, it pushes back the presence of life on Earth at least 400 million years.

Layers of volcanic ash (samples shown in inset) blanket the Arctic seafloor 4,000 meters down. The ash is evidence of an explosive eruption, long thought impossible at those depths.

Fire under ice Thick layers of volcanic ash (above, ash samples shown in inset) blanketing a patch of Arctic seafloor point to explosive volcanism at a depth greater than 4,000 meters, a phenomenon scientists long thought impossible because of the immense pressures at such depths (SN Online: 6/25/08).

Chemical biomarkers in 2.7-billion-year-old Australian rocks, once thought to be the oldest known evidence of complex life on Earth, may have infiltrated long after the sediments were laid down, new analyses suggest.

Dates in doubt Chemical biomarkers in 2.7-billion-year-old Australian rocks, once thought to be the oldest known evidence of complex life on Earth, may have infiltrated long after the sediments were laid down, new analyses suggest (SN: 11/22/08, p. 5).

Trees that grew in Antarctica millions of years ago, when its climate was more mild, had a growth pattern much different from modern trees.

Antarctic trees Trees that grew in Antarctica millions of years ago, when its climate was more mild, had a growth pattern much different from modern trees (SN: 11/8/08, p. 16).

Altogether, meteorites (upper left) that formed early in the solar system’s history contain no more than 250 minerals. About 4 billion years ago, Earth probably had no more than 350 minerals, such as those found in the bedrock of northwestern Canada (upper right). Soon after large amounts of iron ores (lower right) formed about 2.75 billion years ago, Earth had perhaps 1,500 minerals. Today, scientists have identified more than 4,300 types of minerals, including those formed by corals (lower left).

Minerals evolve too In a recounting of the history of mineral evolution, researchers find the number of minerals in the solar system has increased through time, and some minerals on Earth exist because of life (SN: 12/6/08, p. 10).

Firm evidence A ground motion recorded in Japan provides the strongest, most direct evidence that Earth’s inner core (illustrated below) is solid (SN: 9/13/08, p. 14).

New fossils of an ancient, four-limbed creature help fill in the blanks of the evolutionary transition between fish and the first land-adapted vertebrates.

Sea-to-land shift New fossils of an ancient four-limbed creature help fill in the blanks of the evolutionary transition between fish and the first land-adapted vertebrates (SN Online: 6/25/08).

Rock formations that include both marine and terrestrial sediments, such as these 400-million-year-old strata in Brittany, France, yield insight into ancient fluctuations in sea level.

Off the ice A comprehensive record of sea level variations between 542 million and 251 million years ago, compiled from rock strata (one shown right), reveals fluctuations that could have been caused by geological processes other than the formation of massive, land-based ice sheets (SN Online: 10/2/08).

Ancient rocks Scientists may have found the world’s oldest intact rocks in a patch of bedrock on the eastern shore of Canada’s Hudson Bay. Analyses suggest the rocks are about 4.28 billion years old ( SN: 10/11/08, p. 12 ).

Forget bird-brained Paleontologists discover a new species of carnivorous dinosaur, Aerosteon riocoloradensis, that breathed like a bird (SN: 10/25/08, p. 14).

Life down deep As much as 70 percent of the Earth’s microbial life resides on and just below the ocean floor, two new studies suggest (SN: 6/21/08, p. 7).

Small amounts of hydrocarbons emitted from the Lost City hydrothermal vent field (map below shows location) were probably produced by inorganic chemical reactions.

Inorganic building blocks Hydrocarbons in the fluids spewing from a set of hydrothermal vents on the Atlantic seafloor were produced by inorganic chemical reactions within the ocean crust, a finding with implications for the origins of life (SN: 2/2/08, p. 67).