Venus was Earth-like again, but climate change made it uninhabitable

An artist’s interpretation of the surface of Venus. Credit: Shutterstock

We can learn a lot about climate change from Venus, our sister planet. Venus currently has a surface temperature of 450 ℃ (temperature of the self-cleaning cycle of the furnace) and an atmosphere dominated by carbon dioxide (96%) with a density 90 times higher than that of the Earth.

Venus is a very strange place, totally uninhabitable, except probably in the clouds, about 60 kilometers up, where the recent discovery of phosphine may suggest floating microbial life. But the surface is totally inhospitable.

However, Venus once had an Earth-like climate. According to recent climate models, Venus has had much of its history at surface temperatures similar to today’s Earth. It probably also had oceans, rain, maybe snow, maybe continents and tectonic plates, and even more speculatively, maybe even surface life.

Less than a billion years ago, the climate changed dramatically 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 event of climate change that evaporated the oceans and caused the end of the water cycle.

Evidence of change

This climate modeling hypothesis inspired Sara Khawja, a master’s student in my group (co-supervised with geo-scientist Claire Samson), to look for evidence in Venusian rocks for this proposed climate change event.

A radar surface view of Venus aboard the Magellan spacecraft.

Since the early 1990s, my research team at Carleton University – and more recently my Siberian team at Tomsk State University – have mapped and interpreted the geological and tectonic history of Earth’s remarkable sister planet.

The Soviet Venera and Vega missions in the 1970s and 1980s landed on Venus and photographed and assessed the composition of the rocks before the Landers failed due to high temperature and pressure. However, our most comprehensive view of the surface of Venus was provided by NASA’s Magellan spacecraft in the early 1990s, which used radar to see through the dense layer of clouds and produce more detailed images. 98% of the surface of Venus.

Ancient rocks

Our search for geological evidence of the great event of climate change has led us to focus on the oldest type of rock on Venus, called tesas, which have a complex appearance that suggests a long and complicated geological history. I thought that these ancient rocks had the best chance of preserving evidence of water erosion, which is such an important process on Earth and which should have taken place on Venus before the great event of climate change.

Given the low-resolution altitude data, we used an indirect technique to try to recognize the old river valleys. We demonstrated that younger lava flows from the surrounding volcanic plains had filled valleys at the edges of the tissues.

To our amazement, these patterns of fabric valleys were very similar to the patterns of rivers flowing on Earth, which suggested that these fabric valleys were formed by river erosion at a time with Earth-like climatic conditions. My Venus research groups at Carleton and Tomsk State Universities study post-tesserae lava flows for any geological evidence of the transition to extremely hot conditions.

Venus was Earth-like again, but climate change made it uninhabitable

A portion of the Alpha Regio, a topographic area on the surface of Venus, was the first feature on Venus identified from Earth-based radar. Credit: Jet Propulsion Laboratory, NASA

Earth analogues

To understand how volcanism on Venus could produce such climate change, we can look to Earth’s history for analogues. We can find analogies in super-eruptions such as the last eruption in Yellowstone which took place 630,000 years ago.

But such volcanism is small compared to the great magmatic provinces (LIP) that occur about 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 the whole of Canada at 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 eight kilometers.

LIP analogs on Venus include individual volcanoes that are up to 500 kilometers long, extensive lava channels that are up to 7,000 kilometers long, and there are also associated rift systems – in which the crust separates – up to at 10,000 kilometers long.

If LIP-style volcanism was the cause of the great event of climate change on Venus, then could similar climate change occur on Earth? We can imagine a scenario of many millions of years in the future, when several LIPs that appear randomly at the same time could cause the Earth to have such a fleeting climate change, leading to conditions like the current Venus.

The old layered and bent rocks of Venus indicate the volcanic origin

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