500 Million Year Old Embryos

Statements such as "history of life on Earth" is a statement of fact. While there is some evidence that may be supportable, there is no conclusive proof of evolution.

Conclusive proof is not always obtainable. Sometimes the scientist has to settle for a best fit hypothosis. Until someone comes up with a more plausable explanation for the evolving diversity of life forms as evidenced in the geologic record, the highly plausable and widely accepted theory of evolution will have to do.

The geologic history of our planet is under constant revision as new researchers discover new information and postulate incredible new theories that fit the known facts of scientific observations from multiple disciplines. It has been stated that there have been at least five mass extinctions since microbial life first appeared. The timeline above mentions only one; the one that predates the dinosaurs. Then there was the extinction that wiped out the dinosaurs, and another from the snowball Earth ice age, where glaciers covered the globe all the way into the tropics.

What I would like to see is a History of the Earth that includes a timeline of all these events. Anyone?

Check out the link at the bottom of my post. That page has much more detail and I think will have what you're looking for. I mass extinction I included was the worst, wiping out 99% of life on Earth, the others weren't as bad (as far as I've seen). Take a look a the link (At the end of the post, not the first one), it's really great.

Thanks!

I checked it out and discovered how little I knew about the subject. :-)

I was trying to cross reference several of the mass extinction scenarios I've watched on various shows on TV to see where they fit in the timeline. It seems several of them are not yet part of widely accepted geologic history.

Just to name a few by their triggering event in no particular order:
Snowball Earth, the ice age to cover the globe.
Massive lava flows in South America.
Massive lava flows in Siberia that raise global temperatures to the point of triggering a massive methane release from the world's oceans and lowers the oxygen level due to world wide rapid oxidation aka fires.
Asteroid strikes in Gulf of Mexico, triggering massive lava flows on opposite side of the planet in the island of India.

Now the ice record is telling scientists that we may be on the edge of another ice age as the ocean currents slow down their transfer of heat to the polar regions. Last time, it lasted about a thousand years, ending about 15,000 years ago.

There! That's how you stop global warming. This old world can take care of itself after all.

Actually I've heard that warmer ocean currents are being found in both the arctic and antarctic oceans, which is why the ice sheets are melting and breaking up.

This theory was discovered through examination of the geologic record by pulling ice core samples. In my own words, average global temperatures follow a slowly changing pattern of highs and lows with the highs growing increasingly higher, accelerating into a peak or spike and then dropping sharply into an ice age that lasts for around a thousand years.

The mechanism that causes the sudden drop is unknown, but has been postulated to be connected to the ocean currents. In theory, the north bound warm water currents off the coast of New England meet ice sheets at Greenland. The supercooling salt water falls into the deep ocean trench making its way south. It is the cooling and falling of the current that drives the current engine. With climate warming, the ice pack retreats and the current meets with land instead of ice. That, combined with fresh water dilution of the brine, slows then disrupts the currents. Over the following 10 years, winters intensify as ice sheets begin growing again.

In this case, warmer than usual ocean currents would be a symptom of an ice age to come.

It was my understanding that ice ages we consistent with the precession of the earth's tilt. As the tilt angle increases, ice ages result from the more extreme seasons, as the tilt becomes smaller, the planet becomes milder and interglaciation periods occur. Here is a link below that explains it:

http://culter.colorado.edu/~saelias/glacier.html

Theories abound, don't they. Yet, any and all could be true.

The periodicity of each of these causal factors affect climate changes in their own frequency of events, but do not preclude the effects of other factors with a different frequency or mode of change. In fact, given that there are harmonic amplifications in the periodicity between multiple effects might explain the irregularities within the cycles of climate observed in the geologic record.

The long slow changes brought about by the precession of equinoxes, phases of axial tilt and eccentricity of orbit bear little relationship to the phenomenon of a sharp reversal in climate observed in ice core samples. Clearly another theory is called for.

Given also that the current rate of climate change appears to be on a corollary path, and that the end of the interglacial period in this instance is abrupt, the need for understanding is more immediate.

But, it is only a theory.

Yes, in all things there are always a lot of theories. No, not all theories are equal.

Look, of course ocean currents change when climate changes. How could they not. They are not the cause of climate change though, they are a result. The cause is reduced levels of sunlight hitting the Eaths surface.

Over the past million years ice ages have been cyclic with periods that correspond with the periods of precession of the Earths tilt and orbit. Now this is either the biggest coincidence ever or it's the cause.

You need to wake up. Ice on every corner of the planet is melting. Siberia, Alaska, and Tibet's permafrosts are melting, the planet is heating up, not cooling down. The ocean is getting warmer and no vague change in ocean currents is going to eliminate the heat imbalance caused by too much Carbon Dioxide and Methane in the atmosphere.

There's ton's of research on this. This explanation for ice ages has been around for decades and has been correlated in a number of ways.

True enough. I wasn't on a soap box. I was just trying to explain "the theory." That is, the one that was put forth to try to explain the sudden reversal in climate as discovered in the ice record.

I have problems with it too. For instance, if the collapse of the ocean current results in glaciation, then the equatorial region must get hotter, etc. etc.

But, what I see as important to take from it is that world climate can change very quickly. It has before. It will again.

So, we've beat this horse to death. Until there is new information to cover, I'll let it go.

But thanks for a lively discussion.

It is a good discussion, and I can get impatient, so I appreciate your patience. Let me point out what I agree with you on.

I agree the ocean currents change when climate changes. I agree that often these changes are due to an influx of fresh water that disrupts the conveying mechanisms in the ocean which are temperature and salinity based. I agree that disruption of ocean currents has a large effect on local weather and climate.

I don't agree that ocean currents stop. This just can't happen physically because hot water will always flow to cooler areas. Having no ocean circulation is like have a box that has all the air in one side, just doesn't happen because of Thermodynamics. Sudden shifts in the ice core records of antarctica are just local effects. In other words, short periods of time in the ice record give little information about the climate at large in the ice record. Only time scales on the order of 1000 years or more are reliable enough to extrapolate details of the overall climate as opposed to the local antarctic weather.

The way it used to work is the Earth would recieve less sunlight do to precession. The ocean, which is a big climate moderator would start to cool. Because the ocean is an effective heat sink there was a hyteresis between the lower sunlight and the actual cooling. Ocean currents change from a combination of cooling temperatures and salinity causing strong changes in local evironments (for instance the sahara was a grasslands 20,000 years ago). Greenhouse gas levels lower because of the colder environment, finding a new equilibrium. Grounded Ice builds up causing higher reflective further reducing sunlight. Then the sunlight increases do to precession and the whole process would reverse. Everything had a nice set equilibrium.

Now the greenhouse gases are twice as high as they have ever been in the past 1 million years, meaning that the old pattern is gone, we're in unchartered territory here. Equilibrium is displaced and we now have excess heat that is being soaked up by the ocean and being used to melt ice around the world. As the ice melts, there is less reflection so the net sunlight increases. Carbon Dioxide and Methane locked in frozen tundra is released into the environment, raising levels even higher.

Just a quick reply.

Agree that the oceanic currents could never quite stop. They could change their behavior dramatically though, and this could lead to regional (as you stated) climate changes.

The Ice Core Dating

There have been several instances. The dramatic global temperature shift (ice age) I was referring to was something I saw on TV, so unless I accidentally get to view it again I can't tell you the specifics.

But, ... (as Pewee says, "Why is there always a big but?") ... I did find a few references on Wikipedia.

http://en.wikipedia.org/wiki/Ice_core
http://en.wikipedia.org/wiki/EPICA

In the second one:

Information about the core was first published in Nature on 2004/June/10 [1]. The core went back 720,000 years and revealed 8 previous glacial cycles.

A graph of the proxy for temperature indicates gradual increases punctuated by sharp reversals.

I'll look for greenhouse gas records next.

From your EPICA Link Quote:

"The interglacial 400 kyr ago, which is believed (from arguments about the configuration of the orbital parameters of the earth) to be an approximate analogue to the current interglacial, was quite long: 28 kyr"

Notice the phrase regarding orbital parameters. That is refering to the precession of the Earths Orbit about the Sun.

Yes, the 28 Kyr cycle is pretty much a given. But is there an ice age a-commin'? That is the more immediate question.

Are we to roast in the sun bake of unrelenting global warming, or will the planet right itself despite our species pillageing of the land and its energy resources?

Personally, I don't know. It's such a huge question. But, check out this Graph of CO2, temperature, and dust concentration measured from the Vostok, Antarctica ice core.

http://en.wikipedia.org/wiki/Image:Vostok-ice-core -petit.png

There is something completely different in the last 15 Kyrs with temperature. The pointy tip of the cycle is sawed off before matching the previous apex. Does that mean we are 15 Kyrs into a 28 Kyr interglacial period? No cooling help for another 13 Kyrs? Or is there something else worth noting? When did Panama rise up to block the ocean current? Gee, this is complicated.

But, the CO2, while still climbing, is not out of wack from what should be predicted from previous cycles. It is not even "twice as high as they have ever been in the past 1 million years." Unless methane is unusually robust these days. (VBG)

But anyway, the graph doesn't support the theory that I was speaking from either. The previous interglacial didn't end abruptly within a 10 year period as the TV people said.

Perhaps when the summers get unbearable and ruminants quit farting for lack of grass and start dying by the train load, the plant life will come back and soak up some CO2. In the mean time, let's hope that the solar events are few and far between and that the ice don't run out before the party is over.