Archive of chat with David DesMarais

[ Keli/NASAChatHost - 30 - 10:07:31 ]
David will be taking questions during the lecture

[ Keli/NASAChatHost - 31 - 10:10:22 ]
The topic today is "How have the Earth and its biosphere influenced each other over time?"

[ Keli/NASAChatHost - 33 - 10:17:28 ]
To find out more about David, visit http://quest.arc.nasa.gov/ltc/astrobio/desmar/bio.html. You can also find out about his work at http://astrobiology.arc.nasa.gov/

[ Mellie - 34 - 10:28:24 ]
Hello, I'm in high school and am watching during independent study. I think this is very cool and interesting, but I'll have to go soon so I'll ask some questions but then probably get teh answers later today. Thanks

[ Keli/NASAChatHost - 35 - 10:28:25 ]
Okay, Mellie, hope to hear from you.

[ Mellie - 36 - 10:28:51 ]
Dr.DesMarais said that there is some useful things to study in Shark's Bay and in some thermal springs. Does he get to travel to those places? How much time does he spend in the filed vs. in the lab.

[ George - 37 - 10:34:46 ]
How can scientists know how much CO2 there was in the atmosphere 3 billion years ago?

[ Keli/NASAChatHost - 39 - 10:41:21 ]
RE: [Mellie] Wow. Thanks for answring my first question so fast. I read in my paper (San Jose MErcury News) that there was an astrobiology conference last week. At the end of his lecture, could Dr. DesMarais please diverge a bit and say what happened at the conference
Mellie, let's save this one for the end of lecture. Glad you came today.

[ George - 40 - 10:41:48 ]
Did he say that he early life was "pathetic". That seems like a wierd term to use. Did I mishear?

[ Keli/NASAChatHost - 41 - 11:11:26 ]
Dr. Des Marais is now in the chat room and is ready to take your question!

[ Keli/NASAChatHost - 42 - 11:17:28 ]
Dr. Des Marais, I have a question--George asked how we knew how much carbon dioxide was in the atmosphere millions of years ago. You said estimates were made based on the temperature of the earth--but how did we know the temperature of the earth?

[ DavidatAmes - 43 - 11:26:31 ]
Hello! I will be available later on to answer questions that you might have about the lecture on early life or about astrobiology.

[ Keli/NASAChatHost - 44 - 11:27:19 ]
Are there any questions for Dr. Des Marais? And before you leave, please let us know what you thought of today's lecture by giving us feedback at http://quest.arc.nasa.gov/ltc/survey.html

[ Keli/NASAChatHost - 45 - 11:30:57 ]
To find out more about exobiology, visit http://exobiology.arc.nasa.gov/ You can also listen to a talk Dr. Des Marais gave in 1996 entitled "Evolution of the early Earth and its biosphere" at http://astrobiology.arc.nasa.gov/workshops/1996/astrobiology/speakers/desmarais/desmarais.html

[ DavidatAmes - 46 - 11:33:40 ]
RE: [Keli/NASAChatHost] Dr. Des Marais, I have a question--George asked how we knew how much carbon dioxide was in the atmosphere millions of years ago. You said estimates were made based on the temperature of the earth--but how did we know the temperature of the earth?
We can use several lines of evidence to estimate ancient temperatures, but it's a difficult job. First, we see no evidence of extensive glaciation prior to 2.6 billion years ago, so that argues in favor of temperatures that were at least as warm as today. We note that rocks in the earliest land areas weathered very rapidly, and that is consistent with warmer temperatures. We can also examine the stable isotopic composition of oxygen in ancient silica (chert) deposits, because that composition is determined by the isotopic composition of the ocean and by temperature. Those analyses support the interpretation that ancient temperatures were warmer than today's temperatures. This warmth is remarkable, because, as I had said, the sun was less luminous and therefore delivered less solar energy to earth. The inescapable conclusion is that Earth's atmosphere was quite different, and must have caused stronger greenhouse warming.

[ Keli/NASAChatHost - 47 - 11:38:54 ]
Thank you to Netscape for sponsoring this lecture series. Be sure to join us next week at 10:00 am when Dave Peterson talks about "How Do Rapid Changes in the Environment Affect Emergent Ecosystem Properties?"