Did Sea Life Arise Twice? 238
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."
Throw away the Snowball. (Score:5, Interesting)
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:Throw away the Snowball. (Score:3, Interesting)
Water could only have frozen on the surface + geothermal vents to keep the sponges alive.
Re:Dating methods are accurate! (Score:5, Interesting)
***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.
Re:Dating methods are accurate! (Score:3, Interesting)
Unfortunately they aren't accurate. When you have a known decay rate for three different materials, after you calibrate for those differences in decay rate you should get the same answer between all three. Instead what you get is three wildly different numbers. How can you call that accurate?
Re:*At least* once... (Score:2, Interesting)
There is conciderable evedence that all the life we know about is related. For example the direction that DNA curles should chemicly speeking be random, yet all known life has the same direction of curl. This implies a bias most easily explaind by all life having a common anscestor at some point. Whether or not life on Earth at one time formed in series and or parallel with several "first generation" life forms is an open question, but as yet there's lots of evedence in favor of the existance of a universal common anscestor for all known life and none against it.
Re:Life fills a space defined by its environment (Score:1, Interesting)
The fact that life exists on Earth indicates that it most likely exists elsewhere, since the probability of life isn't equal to zero, and there are a ridiculous number of stars and planets.
Basically, the burden of proof is on you to say that life exists only on Earth. That scenario is so unlikely as to not even be funny.
Why does everyone assume that there has to be a default answer to the question, "does life exist on other planets?" As of now, we do not have sufficient proof to answer that question, so we cannot assume positively or negatively. Yes, the burden of proof is on the GP to claim that life only exists on Earth. That is because the burden of proof is on whomever attempts to answer the question as the default is undefined.
Nevermind that the existence of life on other planets is not a conclusion that the GP is trying to make. His premises are that we do not have proof of life and that making conjecture about a topic whose very existence relies on an unproven claim is not science. I agree with that assessment because science requires observation. With no proof of existence, there can be no observation. When we have found extraterrestrial life (which I believe will eventually happen, but belief in a highly probable event is not proof) then we can start analyzing it.
Oh, and to inject a little levity into the discussion... huh huh... panspermia... huh huh... Snowball Earth.
Re:*At least* once... (Score:2, Interesting)
I suppose there's room to mention the theory that life arises all the time but it gets gobbled up by the existing fauna, but we haven't seen it happen, and not for lack of looking.
Re:Life fills a space defined by its environment (Score:5, Interesting)
I've read similar theories (Aquatic ape hypothesis [wikipedia.org]) that stated similar ideas about human evolution. They proposed that humans are poorly adapted to land (relatively speaking). We go through large volumes of water compared to other land based mammals. Humans require far more water and lose more water than most other land based species. We also have very little hair whereas most land based mammals are covered with it. We are also better adapted to water than other apes. The idea was that human ancestors may have been forced back into the oceans, at least partially. Possibly into shallow areas causing adaptions to develop that have changed us in some fundamental way compared to our Ape cousins.
I have always been intrigued by this theory.
Re:Evolution finally refuted (Score:3, Interesting)
A more interesting question would be - have we had intelligent life before on Earth?
Just consider that intelligent life doesn't necessarily mean that there was technology involved. If the intelligence was used for a philosophical society or that the entities having intelligence didn't have hands then the development of tools would have been harder.