Pamela Conrad is an astrobiologist with NASA’s Jet Propulsion Laboratory. She recently gave a lecture explaining how to searching cold deserts on Earth will help scientists understand environments that life could be hiding in the rest of the Solar System. The following article is the first part of an edited transcript of her presentation.
Geologists have built up a suite of tools and techniques that let them peer back in time to watch the formative stages of the Earth and how it’s changed over time – by looking inside rocks. By analyzing trapped water and air in rocks, geologists are studying how our atmosphere changed 3.9 billion years ago, when the crust of the planet was just forming, and there wasn’t any oxygen in the air.
The biggest mass extinction in the Earth’s history happened approximately 250 million years ago. During the “Great Dying”, more than 90% of creatures in the ocean, and 75% of life on land went extinct. What caused the extinction is still up for debate, but a researcher from the University of Washington thinks that low levels of oxygen in the atmosphere sure didn’t help. Oxygen went down to 12% (currently it’s 21%), and this made standing at sea level the same as being atop a 5,300 metre mountain (17,000 feet).
Something wiped out most of the life on Earth 250 million years ago. Evidence has been building that it was an asteroid or comet strike that made Earth unlivable nearly instantly. But other scientists think that it wasn’t instantaneous; instead, they found fossil evidence that the extinction occurred over the course of 10 million years. A group of volcanoes in Siberia spewed out gas continuously that set off a runaway greenhouse effect. Lowered oxygen levels in the atmosphere combined with intense heat would have hit life a deadly double blow.
The European Space Agency’s Envisat earth observation satellite is getting ready for the arrival of an annual event – the opening of the hole in the Earth’s ozone layer. Since a hole first opened up in the mid-1980s, satellites have been tracking its arrival and shape for years, and scientists have gotten quite good at predicting the conditions that will create the gap. The ozone hole should open up in about a week’s time, and then close up again in November or December when higher temperatures around the South Pole will mix ozone-rich air into the region.
When life first arose on the Earth, 4.6 billion years ago, the Sun was putting out 20-25% less energy – our planet should have been an iceball… why wasn’t it? Evidence from ancient rocks shows that there was a large amount of carbon dioxide and methane in the Earth’s atmosphere, which would have helped warm the planet. But these levels were tied to early weather and plate tectonics which carried the greenhouse gasses into and out of the atmosphere, leading to several early ice ages. New research from Stanford has turned up rocks that give an accurate picture of how these gas levels rose and fell over the first few billion years.