Figure 2.
Relevant observations of Earth and Mars. Geologic resurfacing and recycling have erased the overwhelming majority of the Earth's prebiotic history during the Hadean when life may have originated. We propose that Mars, a planet comprised of surfaces that have remained relatively unchanged since their formation, is the best alternative to search for environments consistent with geochemical requirements imposed by the RNA world. *uncertain timing, 1Monteux et al. 2016, 2Pearce et al. 2018, 3Mojzsis et al. 2001, 4Wilde et al. 2001, 5Gomes et al. 2005, 6Boehnke & Harrison, 2016, 7Boussau et al. 2008, 8Gladman et al. 1996, 9Hassenkam et al. 2017, 10Tashiro et al. 2017, 11Allwood et al. 2006, 12Allwood et al. 2009, 13Andrews‐Hanna et al. 2010, Lillis et al. 2013, 15Fassett & Head, 2011, 16Cabrol et al. 2003, 17Fassett & Head, 2008a, 18Goudge et al. 2018, 19Grotzinger et al. 2014, 20Jakosky et al. 2017, 21Ehlmann & Edwards, 2014, 22Grotzinger et al. 2014, 23Hurowitz et al. 2017, 24Squyres et al. 2006, 25Ming et al. 2008