We can learn a lot about climate change from Venus, our sister planet. Venus currently has a surface temperature of 450 ℃ (the temperature of the furnace’s self-cleaning cycle) and an atmosphere dominated by carbon dioxide (96 percent) with a density 90 times that of Earth.
Venus is a very strange place, completely uninhabitable, except perhaps in the clouds about 60 kilometers up, where the recent discovery of phosphine may suggest floating microbial life. But the surface is completely unpleasant.
However, Venus once probably had a terrestrial climate. According to recent climate modeling, for much of its history Venus has had surface temperatures similar to modern Earth. It probably also had oceans, rain, maybe snow, maybe continents and plate tectonics, and even more speculatively, maybe even surface life.
Less than a billion years ago, the climate changed dramatically due to an unbridled greenhouse effect. It can be speculated that an intense period of volcanism pumped enough carbon dioxide into the atmosphere to cause this great climate change, which evaporated the oceans and caused the end of the water cycle.
Signs of change
This hypothesis of the climate modelers inspired Sara Khawja, a master student in my group (co-supervised with geoscientist Claire Samson), to look for proofs in Venusian rocks for this proposed climate change.
Since the early 1990s, my Carleton University research team – and most recently my Siberian team at Tomsk State University – has been mapping and interpreting the geological and tectonic history of Earth’s remarkable sister planet.
Soviet Venus and Vega missions of the 1970s and 1980s landed on Venus and photographed and estimated the composition of the rocks before the landings failed due to the high temperature and pressure. However our most comprehensive view of the surface of Venus was delivered 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.
Our search for geological evidence of the great climate change occurred when we focused on the oldest rock on Venus, called tiles, which have a complex appearance suggesting a long complicated geological history. We thought that these oldest rocks have the best chance of preserving evidence of water erosion, which is such an important process on Earth and should occur on Venus before the great climate change.
Given poor altitude data, we used an indirect technique to try to recognize ancestral river valleys. We demonstrated that younger lava flows from the surrounding volcanic plains filled valleys at the edges of tiles.
To our amazement these layers of valley patterns were very similar to river flow patterns on Earth, leading to our suggestion that these layer valleys were formed by river erosion over time with terrestrial climatic conditions. My Venusian research groups at Carleton and Tomsk State universities are studying the post-tessellation lava flows for some geological evidence of the transition to extremely hot conditions.
To understand how volcanism on Venus could produce such a change in climate, we can look for analogues of Earth’s history. We can find analogies in super-eruptions like the last eruption at Yellowstone, which occurred 630,000 years ago.
But such volcanism is small compared to large igneous provinces (LIPs), which 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, keep in mind that the smallest LIPs produce enough magma to cover the entire Canada to about 10 feet deep. The largest known LIP produced enough magma that would cover an area the size of Canada to a depth of nearly eight kilometers.
The LIP analogues on Venus include individual volcanoes up to 500 kilometers wide, wide lava channels that reach up to 7,000 kilometers long, and there are also associated rift systems – where the crust separates – up to 10,000 kilometers long.
If LIP-style volcanism was the cause of the great climate change on Venus, then could a similar climate change occur on Earth? We can imagine a scene many millions of years into the future, when many LIPs accidentally at the same time could cause the Earth such unbridled climate change leading to conditions like the current Venus.
The ancient layered folded rocks of Venus point to a volcanic origin
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