Venus Was Once More Earth-like, But Climate Change Made It Uninhabitable
Richard Ernst
Read Time: 4 mins
An artist’s rendering of the surface of Venus.(Shutterstock)
We can learn a lot about climate change from Venus, our sister planet. Venus currently has a surface temperature of 450℃ (the temperature of an oven’s self-cleaning cycle) and an atmosphere dominated by carbon dioxide (96 per cent) with a density 90 times that of Earth’s.
However, Venus once likely had an Earth-like climate. According to recent climate modelling, for much of its history Venus had surface temperatures similar to present day Earth. It likely also had oceans, rain, perhaps snow, maybe continents and plate tectonics, and even more speculatively, perhaps even surface life.
Less than one billion years ago, the climate dramatically changed due to a runaway greenhouse effect. It can be speculated that an intensive period of volcanism pumped enough carbon dioxide into the atmosphere to cause this great climate change event that evaporated the oceans and caused the end of the water cycle.
Since the early 1990s, my Carleton University research team — and more recently my Siberian team at Tomsk State University — have been mapping and interpreting the geological and tectonic history of Earth’s remarkable sister planet.
Soviet Venera and Vega missions of the 1970s and 1980s did land on Venus and take pictures and evaluated the composition of the rocks, before the landers failed due to the high temperature and pressure. However, our most comprehensive view of the surface of Venus has been provided by NASA’s Magellan spacecraft in the early 1990s, which used radar to see through the dense cloud layer and produce detailed images of more than 98 per cent of Venus’s surface.
A visualization of Venus’s surface produced by radar on board the Magellan spacecraft.
Ancient rocks
Our search for geological evidence of the great climate change event led us to focus on the oldest type of rocks on Venus, called tesserae, which have a complex appearance suggestive of a long, complicated geological history. We thought that these oldest rocks had the best chance of preserving evidence of water erosion, which is a such an important process on Earth and should have occurred on Venus prior to the great climate change event.
Given poor resolution altitude data, we used an indirect technique to try to recognize ancient river valleys. We demonstrated that younger lava flows from the surrounding volcanic plains had filled valleys in the margins of tesserae.
A portion of Alpha Regio, a topographic upland on the surface of Venus, was the first feature on Venus to be identified from Earth-based radar.(Jet Propulsion Laboratory, NASA)
But such volcanism is small compared to large igneous provinces (LIPs) that occur approximately every 20-30 million years. These eruption events can release enough carbon dioxide to cause catastrophic climate change on Earth, including mass extinctions. To give you a sense of scale, consider that the smallest LIPs produce enough magma to cover all of Canada to a depth of about 10 metres. The largest known LIP produced enough magma that would have covered an area the size of Canada to a depth of nearly eight kilometres.
The LIP analogues on Venus include individual volcanoes that are up to 500 kilometres across, extensive lava channels that reach up to 7,000 kilometres long, and there are also associated rift systems — where the crust is pulling apart — up to 10,000 kilometres long.
If LIP-style volcanism was the cause of the great climate change event on Venus, then could similar climate change happen on Earth? We can imagine a scenario many millions of years in the future when multiple LIPs randomly occurring at the same time could cause Earth to have such runaway climate change leading to conditions like present-day Venus.
About the Author
Richard Ernst, Scientist-in-Residence, Earth Sciences, Carleton University (also a professor at Tomsk State University, Russia), Carleton University
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