SETI Talks: Why is Earth Still Habitable?

SETI Talks

Tags: SETI Talks, Outreach, Planetary Protection, Planetary Exploration

Time: Wednesday, May 19, 2021 -

Location: Online

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Earth, a Pale Blue Dot in our solar system, is also the result of 4 billion years of evolution leading to a technologically advanced and intelligent civilization, humanity. When you look around almost anywhere on Earth, you see life. In the air, in the water, in the land and even underground. But was this inevitable? We know that there have been mass extinction events in the past, some taking out most of life on Earth, but not all of it, since we are here to ponder it.

Current global warming shows us that the climate can change considerably over even a few centuries. Over geological timescales, it is even easier to see climate change. Calculations show that there is the potential for Earth’s climate to deteriorate to temperatures below freezing or above boiling in just a few million years. Abrupt changes can come from natural disasters like super-volcanoes, asteroid impacts, solar flares, supernovae, and many other threatening events. Even the amount of heat from the Sun has increased as it ages, so why is Earth still habitable?

That’s a mystery that we’ll discuss with Sarah Rugheimer and Toby Tyrrell. Sarah is an astrophysicist at Oxford University who studies exoplanet atmospheres, searching for biosignatures and possible life. Toby is a professor in Earth System Science within Ocean and Earth Science, National Oceanography Centre Southampton at the University of Southampton. He recently published a new perspective on why our planet has managed to stay habitable for billions of years.

This work consists of running simulations looking at how 100,000 randomly different planets responded to random climate-altering events spread out across three billion years.

Most of those planets which remained life-sustaining throughout the three-billion-year period only had a probability, not a certainty, of staying habitable.

Is Earth’s success in remaining habitable just a fluke? What can we learn from studying the climate of planets in our solar system and those orbiting other stars?

We hope to answer these questions with our speakers in this conversation moderated by SETI Institute Senior Astronomer Franck Marchis.


Sarah Rugheimer

Dr. Sarah Rugheimer is an astrophysicist at Oxford University working detecting possible life on exoplanets by looking for atmospheric biosignatures. Her research interests are modeling the atmosphere and climate of extrasolar planets, focusing on atmospheric biosignatures in Earth-like planets and modeling early Earth conditions. In 2020 she was selected as a TED Fellow and previously was awarded the Barrie Jones Award and the BSA Rosalind Franklin Lectureship in 2019, and the Caroline Herschel Lectureship Prize in 2018. Her new astrobiology course for the public is available on Amazon Audible Originals, called “Searching for Extraterrestrial Life.”  

Toby Tyrrell

Toby Tyrrell is a Professor of Earth System Science in the School of Ocean and Earth Science at the University of Southampton in the UK. After degrees in engineering, artificial intelligence and computer modeling, in the last 25 years he has created more than ten original computer models in different fields, ranging from neuroscience to plankton ecology to the physics of light in seawater to planetary habitability. In his 2013 book (“On Gaia: a Critical Investigation of the Relationship between Life and Earth,” Princeton University Press), he concluded that the Gaia hypothesis is not supported by current evidence and is therefore not a credible explanation for how Earth stayed habitable. He recently used a simple model to simulate the climate histories of 100,000 planets, each with randomly different climate feedbacks, to assess the roles of destiny and chance in habitability outcomes.