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

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

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

We can learn a lot about climate change from Venus, our sister planet. Venus currently has a surface temperature of 450 ° C (the temperature of a furnace’s self-cleaning cycle) and a carbon dioxide (96 percent) dominated atmosphere with a density 90 times that of Earth.

Venus is a very strange place, completely uninhabitable except perhaps in the clouds about 60 kilometers high, where the recent discovery of phosphine could indicate floating microbial life. But the surface is completely inhospitable.

However, Venus probably once had an Earth-like climate. According to the latest climate models, Venus had surface temperatures similar to today’s Earth for much of its history. It probably also had oceans, rain, maybe snow, maybe continents and plate tectonics, and even more speculative, 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 intense period of volcanism pumped enough carbon dioxide into the atmosphere to cause this major climate change event that vaporized the oceans and ended the water cycle.

Evidence of change

This hypothesis by the climate modelers inspired Sara Khawja, a master student in my group (along with geoscientist Claire Samson) to look for evidence in Venusian rocks for this proposed climate change event.

A visualization of the surface of Venus generated by the radar on board 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 missions Venera and Vega of the 1970s and 1980s landed on Venus and took photos and assessed 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 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 more than 98 percent of Venus’ surface.

Old rocks

Our search for geological evidence of the great event of climate change led us to focus on the oldest type of rock on Venus, the tesserae, whose complex appearance suggests a long, complicated geological history. We thought that these oldest rocks had the best chance of getting evidence of water erosion, which is such an important process on Earth and which should have happened before the great event of climate change on Venus.

Given the poor resolution elevations, we used an indirect technique to identify ancient river valleys. We have shown that more recent lava flows from the surrounding volcanic plains have filled valleys on the edge of the pebbles.

To our amazement, these Tesserae valley patterns were very similar to the river flow patterns on Earth, leading to our suggestion that these Tesserae valleys were created by river erosion during a time of Earth-like climatic conditions. My Venus research groups at the Universities of Carleton and Tomsk are studying the lava flows after Tesserae for geological evidence of the transition to extremely hot conditions.

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

Part of Alpha Regio, a topographical highland on the surface of Venus, was the first feature on Venus to be identified using terrestrial radar. Photo credit: Jet Propulsion Laboratory, NASA

Earth analogies

To understand how volcanism can cause such climate change on Venus, we can look for analogues in the history of the earth. We can find analogies in super-eruptions like the last eruption in Yellowstone, which was 630,000 years old.

However, such volcanism is minor compared to large igneous provinces (LIPs), which occur roughly every 20 to 30 million years. These eruptive events can release enough carbon dioxide to cause catastrophic climate change on Earth, including mass extinctions. To give you a sense of scalability, keep in mind that the smallest LIPs produce enough magma to cover all of Canada to a depth of around 10 meters. The largest known LIP produced enough magma to cover an area the size of Canada to a depth of nearly five miles.

The LIP analogues on Venus include individual volcanoes with a diameter of up to 500 kilometers, extensive lava channels with a length of up to 7,000 kilometers and associated rift systems – in which the crust pulls apart – with a length of up to 10,000 Kilometers.

If LIP style volcanism was the cause of the great climate change event on Venus, could similar climate change be happening on Earth? We can envision a scenario where LIPs occurring randomly several million years into the future could cause Earth to experience such an out of control climate change that results in conditions like today’s Venus.

The ancient layered, folded rocks of Venus indicate volcanic origins

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