Did Sea Life Arise Twice?

eldavojohn writes "Dr. Adam Maloof has found fossils of sea sponges in Australia from 650 million years ago. You might think this is no big deal unless you consider that sea sponges were thought to have arisen 520 million years ago. These fossils predate the oldest hard bodied fossils we have by a hundred million years. Dr. Maloof is now wondering if life might have arisen twice after the first attempt was quashed 635 million years ago: 'Since animals probably did not evolve twice, we are suddenly confronted with the question of how some relative of these reef-dwelling animals survived the Snowball Earth.' So how is it that life survived the Marinoan glaciation? The BBC has a video on the topic and Wikipedia has a time line of the Proterozoic Eon into the Paleozoic Era."

Comments

Throw away the Snowball.

[Remus Shepherd]

More likely, this is evidence that there never was a Snowball Earth. We've never been sure whether the entire Earth froze up or just large areas of it. If creatures lived through the glaciation, that's a good indication that unfrozen regions still existed.

Re:Dating methods are accurate!

[vtcodger]

***Most dating methods that are used routinely are accurate***

True, but unhelpful. Dating techniques useful for dating rocks deposited millions of years ago mostly depend on the use of "index fossils" (fossils that are widely distributed but change enough over time to pin a date down fairly closely.) Less commonly, radiometric dating can be used, but that requires that an event (typically volcanic) reset the atomic clocks in the rocks in question to zero. Since pouring lava over a fossil tends to destroy it, radiometrically dateable fossils aren't all that common. There are a few fossils found between lava flows or buried in volcanic ash that can be dated with fair precision. One especially important set is a collection of difficult to interpret fossils from 595Ma at Fortune Head Newfoundland.