Paul F. Hoffman is a Professor of Geology at Harvard University. His research concerns the history of the earth up to the first appearance of complex animal life. As a field geologist, he has spent over 100 months mapping rock formations in northwestern Canada and southwestern Africa. Born in Toronto, he spent most of his career with the Geological Survey of Canada before moving to the University of Victoria and then to Harvard University. He assembled evidence that plate tectonics began early in the Earth's history and his current research focuses on an extraordinary series of global glaciations that occurred around the time the first complex animals evolved. He is a foreign associate of the U.S. National Academy of Sciences, a foreign honorary member of the American Academy of Arts and Sciences, and a fellow of the Royal Society of Canada.

1.04.01 Larry Carpenter asked:
In theory, if an asteriod or comet caused the snowball earth, could another asteroid or comet help with the warming? As you look at two of the moons of Jupiter, IO and EUROPA, one hot and the other covered in ice, would it be possible that these bodies have a history and future similar to that of Earth?

Hoffman's response:
The climatic effects of large impacts are complex. Initial warming (from kinetic energy of ejecta reentering the atmosphere and consequent burning of terrestrial biomass) lasting for hours to days, is followed by cooling (from dust and soot) for months to years, and finally by warming for centuries to thousands of years if there is a large release of a 'greenhouse' gas like carbon dioxide from rocks in the target area. However, there were apparently no climatic perturbations of the class of a 'snowball' earth following any of the largest impacts in the Earth's crater record (e.g., Chicxulub, Manicouagan, Sudbury, Vredevoort) over the last two billion years. Could a large impact terminate a 'snowball' event, if one were already in progress? Good question!

The moons of Jupiter are far from the Sun, hence their airless surfaces would be extremely cold were it not for internal heat generated from tidal dissipation, due to the elliptical nature of their orbits around the massive planet. Io, being nearer to Jupiter, is more strongly heated: it is the most tectonically active body in the Solar System. Its surface is heated by a continual outpouring of hot lava. Europa's surface is frozen, but various evidence points to the existence of a liquid water ocean at depths of several kilometers below the surface. If life exists in Europa's inner ocean, it will be adapted to conditions perpetually more challenging than those of a 'snowball' Earth.

1.04.01 Roger asked:
I was delighted to see the SciAm Frontiers story about the Cambrian explosion yesterday since I have been reading and thinking about it for a while. I approach the question from a cell biology perspective. In prokaryotes, the genetic material is not isolated inside a nucleus or wound into chromosomes. The evolution from prokaryotes to eukaryotes is fascinating, almost as amazing as the evolution from prebiology to membrane-bound cells that replicate and have a metabolism. Does your theory go into any detail about the means by which the climactic shock you are trying to document affects this change? I.e. why or how would a climactic shock cause cells to form a nucleus or to rearrange the DNA plasmids into chromosomes?

Hoffman's response:
The fossil record of eukaryotic algae goes back definitely at least one billion years, and perhaps two billion years based on more circumstantial evidence. Several major eukaryotic clades were already established before the succession of 'snowball' events near the end of the Proterozoic.

However, there is suggestive evidence that an earlier set of 'snowball' events occurred near the beginning of the Proterozoic, 2.3 to 2.5 billion years ago. Whether these events had anything to do with the evolution of the eukaryotic cell is an open question.

1.30.01 Elham Sarabi asked:
Hi, I am a student at Granada Hills High School and I had a question regarding one of your episodes on "Life's Big Questions." This question is directed to geologist Paul Hoffman: If the Earth was once a frozen solid, then how exactly did the volcanoes come into play and thus resulting to save both our icy planet and our ancestors?

Hoffman's response:
Volcanism stems from movements deep in the Earth's interior, where temperatures reach around 1100 degrees Celsius (the melting point of basalt rock). At this depth, the rocks would barely notice that the Earth's surface had cooled from +15 degrees to -50 degrees! A glacier covering the Earth's surface would resist the penetration by volcanic lava and gasses during an eruption for up to a few weeks, but eventually the red hot lava would melt a hole in the glacier and the gasses would burst through into the atmosphere. If you check old newspapers from the fall of 1999 (I think it was), you will find first-hand reports and photographs of a spectacular volcanic eruption that occurred beneath a large glacier called Vatnajokull in Iceland. The volcano finally broke through to the surface with huge plumes of steam and other gasses, including carbon dioxide.