The gold ring around your finger may symbolize “till death do us part” for you, but for scientists, it poses a problem.

That shiny band probably cost a small fortune at the jewelry store, but gold is actually abundant on the Earth’s surface (which helps explain why it’s the ideal form of money). The difficulty is, when scientists apply what they know about how the solar system formed, it’s hard to explain how all that gold (and other precious metals that bond easily to iron, like palladium and platinum) got into the Earth’s crust, where bling-loving humans could get at it. A new study in Science sets forth an explanation: In the Earth’s younger days, impacts by huge objects—perhaps even one as big as Pluto—may have brought it here.

To explain this theory, let’s start with the most dramatic impact in our planet’s history: the one that formed the moon and re-melted the solidifying Earth in the process.

Moon rocks brought back during the Apollo missions led to the now widely accepted theory that the moon formed when a Mars-size object crashed into early Earth. Energy from the impact would have spurred the still forming Earth to develop its mostly iron core. When this happened, iron-loving metals should have followed molten iron down from the planet’s mantle and into the core. But we know that gold and other iron-lovers are found in modest abundances in Earth’s mantle. [National Geographic]

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A huge spike in the Earth’s atmospheric oxygen about 800 million years ago, the story goes, paved the way for the Cambrian explosion a couple hundred million years later, and with it the rise of complex life. But a new study out in Nature says that picture is incomplete. Researchers found evidence of substantial oxygen 1.2 billion years ago, meaning that the conditions needed for complex life appeared much earlier than scientists knew, and that perhaps something else was required to set off the explosion of biodiversity.

The geologists led by John Parnell hunted in the Scottish Highlands for clues in ancient rocks, where evidence of ancient bacteria could reveal how much oxygen was around 1.2 billion years ago.

Before there was a useful amount of free oxygen around, these bacteria used to get energy by converting sulfate, a molecule with one sulfur atom and four oxygens, to sulfide, a sulfur atom that is missing two electrons. Geologists can get a glimpse of how efficient the bacteria were by looking at two different sulfur isotopes, versions of the same element that have different atomic masses. Converting sulfate to sulfide leaves the rock with a lot more of the isotope sulfur-32 than would be there without the bacteria’s help. [Wired.com]

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Way up in the Great White North, beneath Canada’s Baffin Island, lies material from the very beginning of the planet.

The search for primordial stuff—rocks that have survived 4.5 billion years since the formation of the Earth without being changed by forces that shook and scrambled our planet—is one of geology’s long-running quests. In Nature this week, Matthew Jackson says he may have done it. Jackson’s team found lava rocks in Canada with a signature that matches that of the newly formed Earth, suggesting there is material below the snowy surface that has endured unchanged throughout the planet’s history.

They have the highest proportion of the isotope helium-3 relative to helium-4 of any rocks known. This suggests that the rocks came from a “primitive” region of Earth, as, unlike helium-4, helium-3 can’t be replenished and thus must have come from the original building blocks of the planet. What’s more, the ratio of two isotopes of the element neodymium match what geochemists would expect for a residue from Earth’s early ocean of molten magma [ScienceNOW].

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They went to investigate solar wind-stirred storms in our planet’s magnetic field, but, after working for three years, two NASA solar-powered probes faced a dark demise, trapped in the Earth’s shadow. NASA researchers now think they can give the twin satellites another shot by altering their courses and sending them instead to study the moon.

NASA launched the probes in 2007 as a set of five identical satellites in the THEMIS Mission (Time History of Events and Macroscale Interactions during Substorms), meant to orbit Earth and send information during brief (2-3 hour) “substorms” when the magnetic field surrounding the Earth releases stored energy from solar winds. To understand the start of these “space tornadoes” responsible for the northern and southern lights, NASA placed the probes in very precise orbits, but for two craft that meant, one day, they would face prolonged battery-draining time in the Earth’s shadow.

“When we realized that the satellites would be going into very deep shadows, we started thinking of different methods for saving them–even before they were launched,” lead scientist Vassilis Angelopoulos, at the University of California, Berkeley, told Discovery News. “We realized that if we had enough fuel to change their orbits, the moon’s gravity would start pulling them up.”[Discovery News]

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The bits that make up Earth apparently took their time pulling themselves together. New research hints that our home didn’t form as a fully-fledged planet until 70 million years after its currently accepted birth date, making the planet younger than scientists believed.

The evidence appears in Nature and looks at the Earth’s “accretion”–the swirling together of gas and dust that formed our planet. Researchers previously believed that the Earth’s accretion was a fairly steady process, happening in about 30 million years, but this study suggests that Earth took a lot longer to form.

“The whole issue hinges on working out how long it took for the core of the Earth to form, which is one of the big unknowns in this area of science,” said Dr. John Rudge, one of the authors at the University of Cambridge. “One of the problems has been that scientists usually presume Earth’s accretion happened at an exponentially decreasing rate. We believe that the process may not have been that simple and that it could well have been a much more staggered, stop-start affair.” [The Telegraph]

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Here we are drinking coffee and tweeting and otherwise going about our lives, generally not giving much thought to the protection that the Earth’s magnetic field affords us from the solar wind. But that magnetic field is crucial for our existence. Now, new findings in Science say that this protective shield originated even 200 million years earlier than scientists had previously thought, perhaps protecting the planet’s water from evaporating away and aiding the rise of life on the early Earth.

To know about the planet’s magnetic field three and a half billion years ago, you need iron, which records not only the direction but also the strength of the magnetic field when it forms. In South Africa, study leader John Tarduno and his team found quartz with iron tucked inside that had remained unchanged in all those years. Using a specially designed magnetometer and improved lab techniques, the team detected a magnetic signal in 3.45-billion-year-old rocks that was between 50 and 70 percent the strength of the present-day field, Tarduno says [Science News]. Three years ago he made a similar find in rocks 3.2 billion years old; thus, this find pushes back the Earth’s magnetic field at least another 200 million years.

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This dazzling picture of our planet, all dark but the cerulean sliver of the South Pole, was a long time coming.

Rosetta, a European Space Agency craft, captured this view of the crescent Earth from about 400,000 miles away. The unmanned probe, which is busy chasing comets, was making its third flypast since it was launched in 2004. The close approach gave it a speed boost to send it on its mission to Comet Churyumov-Gerasimenko [Scientific American].

This will be Rosetta’s final visit to its home planet, having already executed a flyby of the asteroid Steins, a gravity assist with Mars, and two previous swoops past the Earth, gathering images all the way. Now it’s off to the comet.

Rosetta is carrying a fridge-sized lab, Philae, that it will send down to the comet. Anchored by tiny hooks, Philae will look for clues about the Solar System’s primal past, exploring a theory that comets are primitive rubble left over from the making of the Solar System [AFP].

While we bid safe travels to Rosetta, it could tell us something about the Earth itself on this final pass. Scientists notice unexpected behavior in spacecraft that make gravitational assists with our planet: Rosetta itself behaved exactly as expected in 2007 flyby but picked up an extra speed boost of 1.8 millimeters per second on its initial maneuver in 2005, leading some mission scientists to speculate that the Earth’s rotation might be distorting space-time more than they thought. “Some studies have looked for answers in new interpretations of current physics. If this proves correct, it would be absolutely groundbreaking news” [MSNBC], says Rosetta flight dynamics specialist Trevor Morley.

Related Content:
Bad Astronomy: Rosetta Takes Some Home Pictures
Bad Astronomy: Earth From Rosetta, from its 2007 flyby.
Bad Astronomy: Rosetta Swings By Mars!
DISCOVER: To Catch a Comet, which anticipated Rosetta, Stardust, and other comet-chasing missions.

Image: ESA