An artistic representation of the surface of Venus. Image via Shutterstock / The conversation.
By Richard Ernst, Carleton University
We can learn a lot about climate change from Venus, our sister planet. Venus currently has a surface temperature of 840 degrees F (450 degrees C) – the temperature of a furnace’s self-cleaning cycle – and an atmosphere dominated by carbon dioxide (96%) with a density 90 times that of the soil.
Venus is a very strange place, totally uninhabitable, except perhaps in the clouds some 60 kilometers above the ground, where the recent discovery of phosphine may indicate floating microbial life. But the surface is totally inhospitable.
However, Venus probably once had an earthly climate. According to recent climate models, for much of its history, Venus had surface temperatures comparable to today’s Earth. It probably had oceans, rain, maybe snow, maybe continents and plate tectonics, and more speculatively, maybe even surface life.
Less than a billion years ago, the climate changed dramatically as a result of a runaway greenhouse effect. It can be speculated that an intense period of volcanism pumped enough carbon dioxide into the atmosphere to cause this major climate change that evaporated the oceans and caused the end of the water cycle.
Evidence of change
This hypothesis of the climate models inspired Sara Khawja, a master’s student in my group (co-supervised with geoscientist Claire Samson), to search Venusian rocks for evidence for this proposed climate change.
Since the early 1990s, my research team from Carleton University – 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 landed on Venus and took photos and evaluated the composition of the rocks, before the landers failed due to the high temperature and pressure. However, our most comprehensive view of Venus ‘surface was 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 over 98% of Venus’ surface. .
A visualization of the surface of Venus 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 reminiscent of a long, complicated geological history. We thought these oldest rocks had the best chance of preserving evidence of water erosion, which is such an important process on Earth and should have happened on Venus before the great climate change.
Given the poor-resolution elevation data, we used an indirect technique to try to identify ancient river valleys. We showed that younger lava flows from the surrounding volcanic plains had filled valleys in the edges of tesserae.
To our surprise, these tesserae valley patterns were very similar to the flow patterns of Earth’s rivers, leading to our suggestion that these tesserae valleys were formed by river erosion at a time with Earth’s climatic conditions. My Venus research groups at Carleton and Tomsk state universities study post-tesserae lava flows for geological evidence of transition to extremely hot conditions.
A portion of Alpha Regio, a topographic highland on the surface of Venus, was the first feature on Venus to be identified by an Earth-based radar. Image via NASA-JPL.
Earth analogies
To understand how volcanism on Venus could cause such a climate change, we can look to Earth’s history for analogues. We can find analogies in super eruptions such as the last eruption near Yellowstone that happened 630,000 years ago.
But such volcanism is small compared to major coagulation provinces (LIPs) that occur approximately every 20-30 million years. These eruptions could release enough carbon dioxide to cause catastrophic climate change on Earth, including mass extinctions. To give you an idea of scale, consider that the smallest LIPs produce enough magma to cover all of Canada to a depth of about 10 meters. The largest known LIP produced enough magma that would have covered an area the size of Canada to a depth of nearly 8 km.
The LIP analogues on Venus include individual volcanoes up to 500 kilometers in diameter, extensive lava channels that can reach up to 7,000 kilometers in length, and there are also associated rift systems – where the crust pulls apart – up to 10,000 km in length.
If LIP-like volcanism was the cause of the great climate change on Venus, could a similar climate change happen on Earth? We can envision a scenario many millions of years into the future where multiple LIPs occurring randomly at the same time could cause Earth to experience such a runaway climate change leading to conditions like today’s Venus.
Richard Ernst, Scientist-in-Residence, Earth Sciences, Carleton University (also professor at Tomsk State University, Russia), Carleton University
This article has been republished from The conversation under a Creative Commons license. Read the original article.
In short, Venus has a surface temperature of 840 degrees F (450 degrees C) and an atmosphere dominated by carbon dioxide, with a density 90 times that of Earth. However, for much of its history, Venus likely had a terrestrial climate, with oceans, rain, perhaps snow, perhaps continents and plate tectonics, and even more speculatively, perhaps even surface life. Then, less than a billion years ago, Venus’s climate changed dramatically due to a runaway greenhouse effect.
