Raindrops Tell The Story of Earth’s Ancient Atmosphere

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A thicker atmosphere slows the speed of falling water. Image Credit: stempl

What happens when those raindrops hit the ground? As anyone who has participated in a water balloon fight can tell you, water that moves at great speed makes a large splash. Since the atmosphere impacts the speed of the water, this means that the thicker the atmosphere, the smaller the splash.

Slower Rain, Thicker Atmosphere

What does this all have to do with the ancient earth?  By measuring the size of raindrop fossils and comparing them to the size of modern raindrop splashes, Som, and his colleagues David Catling and Roger Buick of UW Earth and space sciences: Jelte Harnmeijer, a UW graduate, and Peter Polivka, a UW graduate student in civil engineering, discovered that ancient raindrops made smaller impressions than their modern counterparts. They did this by dropping modern raindrops into volcanic ash, then comparing the sizes of the raindrops’ impressions with the size of fossilized raindrop impressions.

What they found helps clear up some of the mystery around the earth’s ancient climate. Billions of years ago, the sun put out 30 percent less light than it does now. While the earth should have been frozen, it was not. Rivers and oceans ran freely. While scientists have long speculated as to reasons why water could exist on earth during this cold time, the investigation of ancient raindrops may point to a cause. The ancient raindrops likely fell through a thick atmosphere full of greenhouse gases. These abundant greenhouse gases warmed the planet, making it a very different place than it is today.

This study of the ancient climate highlights the Earth’s capacity for extreme transformation. From an Earth teeming with microbial life, to an Earth chock full of humans, the planet’s atmosphere moderates heat and light, transforming the planet’s ability to host different forms of life. This slow but radical transformation in the atmosphere has turned the earth into a very different planet.

References

Som, S. M., Catling, D., Harnmeijer, J., Polivka, P., Buick, R. Air density 2.7 billion years ago limited to less than twice modern levels by fossil raindrop imprints. (2012). Nature. Accessed April 9, 2012.

Stricherz, V. Fossil Raindrop Impressions Imply Greenhouse Gases Loaded Early Atmosphere. (2012). University of Washington. Accessed April 9, 2012.

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