Privileged Planet: earliest water (Introduction)

by David Turell , Monday, June 03, 2024, 18:09 (105 days ago) @ David Turell

Four billion years ago:

https://www.sciencenews.org/article/freshwater-earth-ancient-crystal-years

"Researchers analyzed oxygen molecules within 4-billion-year-old zircon crystals from Western Australia’s Jack Hills, one of the oldest rock formations on Earth. The relative proportions of oxygen’s heaviest and lightest forms, or isotopes, in the zircons are possible only if there been a significant amount of freshwater present, geochemist Hamed Gamaleldien of Khalifa University in Abu Dhabi and colleagues report June 3 in Nature Geoscience.

"The finding suggests that freshwater may have been actively cycling on Earth hundreds of millions of years earlier than previously thought. Past studies have found evidence that a robust water cycle, one that involved rain and evaporation from the land back to the atmosphere and then rain again, existed by at least 3.2 billion years ago.

"Even if there was a freshwater cycle 4 billion years ago, that doesn’t mean there was necessarily life on Earth that far back, Gamaleldien says. “But at least we have the main ingredient to form life.” Currently, the oldest agreed-upon evidence for life on Earth comes from fossilized microbial mats, or stromatolites, in Australia’s Strelley Pool Chert (SN: 10/17/18). Those stromatolites date to 3.5 billion years ago.

"Cycles of evaporation and rain alter the chemical makeup of water molecules. When water evaporates from the ocean’s surface, leaving the salt behind, the lighter form of oxygen, oxygen-16, tends to evaporate faster than the heavier oxygen-18. That lighter water may then rain out over land, and perhaps evaporate again. Over time, the freshwater becomes more concentrated in oxygen-16 compared with the original seawater.

"When that rainwater percolates through the ground, it can chemically react with the rocks themselves, or with magma within the rocks, imparting those lighter isotopic oxygen values — indelible clues that freshwater was present.

"The researchers analyzed oxygen isotopic ratios of more than 1,300 zircons. Most of the zircons had relatively heavy oxygen isotope values, as would be expected from seawater. But at two time periods, around 3.4 billion years ago and 4 billion years ago, the ratios indicated a greater proportion of lighter oxygen.

***

"The team then ran thousands of computer simulations to determine the likelihood of different explanations for the observed ratios. “We concluded that the main water on Earth was oceanic,” or salty, Gamaleldien says. “But only when we used freshwater [did] it create the results we see.” Furthermore, he says, the findings also suggest that enough land had emerged above sea level by that time to support a water cycle. Researchers have pondered whether Earth was completely covered by oceans between around 3 billion and 4 billion years ago.

"Gamaleldien and colleagues present a convincing case that there was freshwater cycling on Earth 3.4 billion years ago, corresponding to previous evidence for freshwater on Earth, says geochemist Jesse Reimink of Penn State. But “the jury’s still out” on whether that was the case 4 billion years ago."

Comment: whenever fresh water appeared there had to be land for it to fall on. In a purposeful design approach, develop organisms in the ocean, then have them move to land for more complex forms with larger more complex brains. It is a logical pattern such as a designer would produce.