The oldest "drop" of water ever discovered on Earth is estimated to be between 1.5 billion and 2.6 billion years old. This ancient water was found deep within the Kidd Creek Mine in Ontario, Canada, approximately 2.4 kilometers (1.5 miles) below the surface. Geologists from the University of Toronto discovered that this water had been trapped in isolation inside rock fractures for eons, completely cut off from the Earth's surface and the modern water cycle. By analyzing the isotopes of noble gases (like Xenon and Helium) trapped within the liquid, scientists were able to "fingerprint" its age. Surprisingly, the water was found to be highly saline—about ten times saltier than seawater—and contained chemical energy that could support microbial life in the absence of sunlight. This discovery in 2013 (and subsequent older samples found in 2016) has profound implications for the search for life on Mars and other planets with deep subsurface water.