Life on Earth depends on liquid water and the temperature at which it freezes or boils. How much would the values of 0掳C and 100掳C need to change to make life here unsustainable, or hugely different?
鈥� Due to its strong hydrogen bonding, water has a high freezing and boiling point for its molecular weight of 18. In comparison, ethane, with a molecular weight of 30, freezes at -182.8掳C and boils at -88.5掳C. If water had the same level of hydrogen bonding as ethane, it would freeze and boil at much lower temperatures, and Earth as we know it would be dry.
Organisms seem to require a liquid solvent for transporting materials, so Earth might be lifeless if water boiled at around 40掳C. This is because water vapour is a greenhouse gas. Once runaway evaporation of the oceans began, the temperature would rise, causing ever more evaporation.
Advertisement
Similarly, if water turned to ice at say 30掳C, all the planet鈥檚 oceans would freeze right down to the sea floor. In this scenario, runaway cooling from reflective white ice wouldn鈥檛 be counteracted by any amount of carbon dioxide emissions, leading to a permanent 鈥渟nowball Earth鈥�.
However, one could argue that life maintains its own conditions for survival. The limits for life as we know it are then how much heat or cold organisms can tolerate. We have thermophilic organisms that can live above 120掳C, while psychrophilic bacteria can live at -20掳C. So life could probably exist in some form even if water boiled at 0掳C or froze at 100掳C.
Hillary Shaw, Newport, Shropshire, UK
We pay 拢25 for every answer published in 麻豆传媒. To answer this question 鈥� or ask a new one 鈥� email lastword@newscientist.com.
Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.
麻豆传媒 retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.
You can also submit answers by post to: The Last Word, 麻豆传媒, 25 Bedford Street, London WC2E 9ES.