Size and distribution of bubbles trapped in lava flows from billions of years ago point to much lower air pressure than today’s atmosphere.

DENVER―May 6―A new process for analyzing ancient bubbles trapped in lava sheds light on the Earth’s atmosphere and its evolution over billions of years. Researchers at the Denver Museum of Nature & Science, along with colleagues at the University of Washington and the University of Western Australia, used a CT scanner to analyze the size and distribution of gas bubbles within lava flows that solidified an estimated 2.7 billion years ago.

“Since no one was around billions of years ago to collect and store atmospheric samples, we rely on proxies, such as the gas bubbles trapped in lava rocks, to determine what the atmosphere was like at the time and help inform how it has changed over time,” said James Hagadorn, curator of geology at the Denver Museum of Nature & Science. “And what these fossilized bubbles tell us is that our atmosphere has changed a lot.”

The scans, along with other proxies, such as raindrops fossilized in stone and rusting of minerals in ancient river deposits, provide evidence that Earth’s atmosphere was twice as thin 2.7 billion years ago as it is now. The results also point to an ancient atmosphere that was rich in greenhouse gases and that it greatly fluctuated over the course of time.

These findings contribute to a refined understanding of the degree to which temperatures varied and how resilient Earth is.

“The entire scientific community has a vested interest in these results,” said Hagadorn. “This CT scanning technique can be applied in a variety of ways to study other celestial bodies and their atmospheric evolution. Just imagine putting one of these on a Mars rover to study the lava flows that cover its surface!”

To determine ancient atmospheres from fossilized lava, it is necessary to know the elevation from which the sample was taken. The researchers only took samples from lava solidified on ancient beaches and tidal flats to ensure elevation was known. 

Dozens of samples were taken and cored with a special drill. These samples were then scanned at the Denver Museum of Nature & Science on a microfocus X-ray CT scanner. Unlike scanners used on humans, this one emits higher-energy X-rays that can penetrate dense objects like rock, and can image microscopic structures really well, such as bubbles a tenth the size of a period. Each scan took half a day to complete. The data from the scans was then processed to make three-dimensional images of the bubbles located deep inside the rock samples. 

The full report will be available online via “Nature,” the international weekly journal of science, once the embargo has lifted. Enter digital object identifier (DOI) 10.1038/ngeo2713 to access the paper.

NOTE: Photos available.