Called the Hadean period in reference to the Greek term for hell (Hades), the first 700 million years of Earth's history was a time when the planet was bombarded by deadly meteorites. Now, however, most geologists have accepted the idea that single-celled organisms could have lived through these catastrophic hits. And the article just published in Nature reveals that the early planet probably had land masses and bodies of water.

By examining zircons, a type of crystal found in 4 billion-year-old Australian rocks, a team of U.S. scientists determined not only that water had been present in the area at the time, but that the rocks had existed in a chunk of cooled planetary crust caused by plate tectonics. Plus, the planet was likely a lot cooler than previously imagined, though probably hotter than it is today.

The temperature difference would have been caused partly by plate tectonics, which leeches greenhouse gasses from the air as it churns the Earth's crust. But that temperature would also have been affected by the weakness of the young sun, which put out 30 percent less energy than it does today.

These new theories about the early Earth help explain why geologists have discovered signs of life blooming all over the planet starting about 3 billion years ago. In fact, life was probably evolving for as much as a billion years before that. And except for those occasional apocalyptic meteor hits, life evolved on a planet whose climate might not have been all that different from the one we experience today.

Low Heat Flow Inferred from Zircons [via Nature]

A New View of Early Earth [via NYT]

Image via New York Times (Left, Bruce Watson; right, Don Dixon).

According to the Geological Survey of Finland, which created the map out of years of survey research:

This map is the first global compilation of the wealth of magnetic anomaly information derived from more than 50 years of aeromagnetic surveys over land areas, research vessel magnetometer traverses at sea, and observations from earth-orbiting satellites, supplemented by anomaly values derived from oceanic crustal ages. The objective is to provide an interpretive dimension to surface observations of the Earth’s composition and geologic structure. Metamorphism, petrology, and redox state all have important effects on the magnetism of crustal materials.

The magnetic anomalies represented on this map originate primarily in igneous and metamorphic rocks, in the Earth's crust and possibly, uppermost mantle. Magnetic anomalies represent an estimate of the short-wavelenght (< 2600 km) fields associated with these parts of the Earth, after estimates of fields from other sources have been subtracted from the measured field magnitude. In most places the magnetic anomaly field is less than 1 per cent of the total magnetic field.

Magnetic Anomaly Map of the World [via Commission for Geological Maps of the World]

He writes:

The magnetic field deflects a lot of the Sun’s incredibly nasty radiation, so if you take it away, we could all get microwaved to a crisp.

Even scarier: The Earth's magnetic field has weakened by ten percent over the last 160 years. Does that mean we're due for a flip? Dan Lathrop, a geophysicist at University of Maryland, will try to find out when he spins up his mega steel ball and recreates (on a small scale) the magnetic conditions on Earth. [via Collision Detection]

Mercury is about twice as big as pluto, but still is the smallest object called a "planet" orbiting the Sun. The question is: how much smaller will it get? It will never get anywhere near as small as the former ninth planet, but will the IAU see fit to demote it too as it continues shrinking? Only time will tell.

Meanwhile, Mercury's molten iron core continues to cool, shrinking the planet from the inside. Small particles of solid iron 'snow' rain down toward the ever-widening solid core. But even as the solid grows it's denser than the liquid and so takes up less space. This has been going on probably for billions of years and over time the shrinkage has caused Mercury's crust to buckle and fold up on itself, as seen here (that y-shaped fracture in the left side of the image is a huge fracture in the rock. The whole picture is about 200 kilometers wide):

(from NASA)

On the right hand side of the image, the craters with the soft-looking rims appear to be old impact basins that have been filled in with lava, indicating the Mercury once had some serious volcanoes exploding on its surface. Why did the volcanoes die off? Mercury cooled off. Just like on Mars and the Moon, Mercury was fiery when it first came into being, but lost its heat in the roughly 4.5 billion years since, silencing is volcanic activity. Earth is cooling in a similar way and in a few billion years it will get too cold for volcanoes too. When it does it will go quiet forever.

Source: Science, NASA, via LA Times

Geophysics professor Gregory P. Waite published his work recently in the Journal of Geophysical Research. A summary of it explains:

Volcanoes don't always erupt suddenly and violently. The most recent eruption of Mount St Helens, for example, began in October 2004 and is still going on. It's what Waite and other volcanologists call a passive eruption, with thick and sticky lava squeezing slowly out of the ground like toothpaste from a tube . . . When a volcano such as Mount St Helens erupts, it can cause a series of shallow, repetitive earthquakes at intervals so regular that they've been called "drumbeat earthquakes."

The fluid in the crack most likely is steam, derived from the magma and combined with water vaporized by the heat of the molten rock. A continuous supply of heat and fluid keeps the crack pressurized and the "drumbeats" beating.

A Fresh Look Inside Mount St Helens [Michigan Tech]