Venus was similar to Earth again, but climate change made it uninhabitable

Artist’s impression 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 ℃ (the temperature of an oven’s self-cleaning cycle) and an atmosphere dominated by carbon dioxide (96%) with a density 90 times that of the Earth.

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

However, Venus probably once had an Earth-like climate. According to recent climate models, for much of its history Venus has had surface temperatures similar to those of today’s Earth. It probably also had oceans, rain, perhaps snow, perhaps continents and plate tectonics, and even more speculatively, perhaps 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 evaporated the oceans and caused the end of the water cycle.

Proof of change

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

A visualization of the surface of Venus produced by radar aboard the Magellan probe.

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

The Soviet Venera and Vega missions 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% of the surface. 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 rocks on Venus, called tesserae, which have a complex appearance that suggests a long and complicated geological history. We thought these older rocks had the best chance of preserving evidence of water erosion, which is such an important process on Earth and should have occurred on Venus before the great climate change event.

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

To our amazement, these valley tile patterns were very similar to the flow patterns of rivers on Earth, which led us to suggest that these tile valleys were formed by river erosion during a period with Earth-like climatic conditions. . My Venus research groups at Carleton and Tomsk state universities are studying post-tessellation lava flows for any geological evidence of transition to extremely hot conditions.

Venus was similar to Earth again, but climate change made it uninhabitable

A portion of Alpha Regio, a topographical plateau on the surface of Venus, was the first feature on Venus to be identified by Earth’s radar. Credits: Jet Propulsion Laboratory, NASA

Analogies with the Earth

To understand how volcanism on Venus can produce such a change in climate, we can look at the history of the Earth for analogues. We can find similarities in super-eruptions such as the last eruption at Yellowstone that occurred for 630,000 years.

But such volcanism is small compared to large igneous provinces (LIPs) that occur approximately every 20-30 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 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 it would cover an area the size of Canada to a depth of nearly eight kilometers.

LIP analogues on Venus include single volcanoes up to 500 kilometers in diameter, extensive lava channels reaching a length of up to 7,000 kilometers, and there are also associated rift systems – where the crust is separating – up to 10,000 kilometers long. .

If LIP-style volcanism were the cause of the great climate change event on Venus, then could a similar climate change occur on Earth? We can imagine a scenario of many millions of years into the future where multiple LIPs randomly occurring at the same time could cause such uncontrolled climate change on Earth that it leads to conditions like today’s Venus.

The ancient layered and folded rocks of Venus indicate volcanic origin

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