Marinoan sponges?!?
A graduate of my summer Snowball Earth course just forwarded me a link to a news item about a recent discovery which finds biomarkers exclusive to the sponges during Marinoan-glaciation-aged sediments on the Arabian Peninsula. The strata are "at least 635 million years old."
This is significant because the usual line about Snowball Earth is that multicellular animals show up after the glaciations end, not during. So what's going on here? Looks like we didn't understand the thing as well as we thought. For many people, the co-incidence (in the most literal sense) in timing between the end of the glaciations and the first multicellular animal fossils was one of the most intriguing things about the Snowball hypothesis -- we all want to know where we came from, after all -- and this may take some of the wind out of those sails. As humans, we like a good story, and this may be one reason the idea of a Snowball Earth is such a popular notion: it's a dramatic story about where we came from, and one that stretches our conception of the limits of change on our planet. But now that story exhibits a flaw upon closer scrutiny, and it makes it less satisfying. The consolation prize is that event though the story isn't as neat, it's closer to the truth. That's the way science works -- especially earth science, which isn't often as tidy as a fairy tale.
Hat tip to Christina T. for passing this on!
UPDATES: (1) Chuck read the paper and wrote it up at his blog. (2) WIRED magazine is also reporting on this, calling the discovery the world's "oldest animal fossils." I'm not sure I agree with that phrasing -- but that probably stems from my lack of familiarity with the reliability of biochemical signatures over traditional body or trace fossils.
This is significant because the usual line about Snowball Earth is that multicellular animals show up after the glaciations end, not during. So what's going on here? Looks like we didn't understand the thing as well as we thought. For many people, the co-incidence (in the most literal sense) in timing between the end of the glaciations and the first multicellular animal fossils was one of the most intriguing things about the Snowball hypothesis -- we all want to know where we came from, after all -- and this may take some of the wind out of those sails. As humans, we like a good story, and this may be one reason the idea of a Snowball Earth is such a popular notion: it's a dramatic story about where we came from, and one that stretches our conception of the limits of change on our planet. But now that story exhibits a flaw upon closer scrutiny, and it makes it less satisfying. The consolation prize is that event though the story isn't as neat, it's closer to the truth. That's the way science works -- especially earth science, which isn't often as tidy as a fairy tale.
Hat tip to Christina T. for passing this on!
UPDATES: (1) Chuck read the paper and wrote it up at his blog. (2) WIRED magazine is also reporting on this, calling the discovery the world's "oldest animal fossils." I'm not sure I agree with that phrasing -- but that probably stems from my lack of familiarity with the reliability of biochemical signatures over traditional body or trace fossils.
Labels: chemistry, fossils, geology, porifera, proterozoic, snowball earth
