Venus considered for clues on early Earth geology

Venus considered for clues on early Earth geology
Hinode Views of Venus transit in 2012. Credit: NASA's Marshall Space Flight Center

Imagine thousands of huge asteroids raining down on ancient Earth, smashing craters as big as metropolitan Perth and a few much larger rocks which gouged holes as big as Australia into the planet.

These impacts of epic proportions during the Late Heavy Bombardment period (4.1 to 3.8 billion years ago) caused major changes to the planet's geology and supposedly kicked off the formation of continents more than 2.5 billion years ago, according to UWA Gledden Visiting Fellow Professor Vicki Hansen.

Her assertions are based on her decades-long research of Earth's sister planet, Venus, and were presented at a recent public lecture.

Early Earth's geology is shrouded in mystery because plate tectonics—the huge plates of crustal material that 'float' across the surface of Earth, creating continental drift—have removed much of the evidence.

It is possible to determine what Earth may have once been like by studying another world such as Venus which offers a similar location in the solar system and is roughly the same size and density as Earth, but does not have plate tectonics, Prof Hansen said.

"Pages of Earth's geologic baby-book are worn, torn, and mostly destroyed; in contrast, Venus' baby book remains intact, with perhaps a few folds and wrinkles," Prof Hansen said.

Asteroid showers, geologic "baby-books" and lava ponds

Venus' surface is also shrouded in mystery thanks to a thick layer of sulphuric acid cloud floating in an atmosphere of carbon dioxide, so Prof Hansen and her team used data from NASA's Magellan spacecraft to examine the planet's geology.

In the early 1990's Magellan used radar to map 98 per cent of Venus in spectacular detail through the clouds, and now geologists can 'read' this rich geological record to construct a picture of its global evolution.

"We found evidence of huge ponds of ancient lava, but they exist on raised plateaus, so how could such a raised pond form?" Prof Hansen said.

With the help of computer models, she concluded an asteroid pierced the crust and partially melted the mantle beneath, and this melted material rose to create the lava pond on top of the crust.

This process increased the crust's volume and made it less dense, or 'buoyant', so that it raised the pond above the surrounding area.

Similar processes here on Earth would explain how the cores of the continents—the so-called Archean cratons—became 'buoyant' at a similar time in the planet's evolution when giant asteroids showered both planets.


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Impact origin of archean cratons: Learning from Venus

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This article first appeared on ScienceNetwork Western Australia a science news website based at Scitech.

Citation: Venus considered for clues on early Earth geology (2015, October 30) retrieved 17 July 2019 from https://phys.org/news/2015-10-venus-clues-early-earth-geology.html
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Oct 30, 2015
The Venus Pioneer mission found that Venus is not in thermal equilibrium. In fact, it found that it's releasing 15% more heat than it's taking in. The excess heat was considered "embarrassing" and scientists wished it away, because Carl Sagan's Super Greenhouse Theory could not be assumed to be correct with such a disparity.

Such a large amount of excess heat raises one very important question: Is it really true that Venus is an old planet? The numerous probes involved with the Venus Pioneer mission appeared to point to the planet's surface as the heat's source. But, this was so unexpected that the theorists decided to "correct" the data to reflect the assumptions necessary for Sagan's greenhouse theory.

These original papers are snapshotted here:

https://plus.goog...2QRETTAy

It's very hard to find anybody today who even knows anything about this history.

Oct 30, 2015
There you go again, linking to Chris Reeve's G+ page.

Error connection is common in science and the paper is freely accessed. Read it and explain what the authors got wrong, be specific.

http://ntrs.nasa....5226.pdf

Oct 30, 2015
Interesting approach, but the result sounds like a hugely speculative lecture. Lava ponding wouldn't predict the TTG/granite geology of the early/late cratons, nor the absence of impact shocks in the zircon record before 3.5 Ga bp.

But we can't say much before it is published through peer review. This seems to be the lecture in question: http://www.ias.uw...s/hansen . "The recording of this public lecture is not available."

@Vietviet: I admire anyone who can convince their stomachs to even glance at crank theology. Their beliefs churn the stomach of most rational beings. Maybe it was that pizza I had ... No. It's their disregard of known science and their play at pretend science that is disgusting.

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