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coliver
2009-Jan-30, 08:20 AM
I recently read an article that scientists are examining a new theory that the Earths core is actually two separate cores that merged. I had mentioned a comet as a possible occurence that led to lifes evolution about 10,000 years ago in a previous thread. Could it be possible that an icy moon or planet could have collided with Earth around that time? Just wondering if it was even possible? Or if it would make sense?

Murphy
2009-Jan-30, 08:31 AM
Doesn't make much sense to me. And what's this about life evolving 10,000 years ago, last time I checked the earliest know date for life was about 3.8 Billion years ago. I mean in 8000 BC Humans were already all over the planet and some of them were even farming.

Now on to this comet thing, I highly, highly doubt that any collision with a comet or even a large icy moon could disrupt the Earth's core, and I certainly don't think any material from any impact (short of a planet sized one) would penetrate to the core.

And I think we would know if something as big as a moon hit us just 10,000 years ago as it would have caused a huge mass extinction (in fact it would probably wiped out all life). I don’t think there's any evidence for a large comet hitting Earth in that timeframe either, although there have been possible "comet fragments" like the Tunguska impact of 1908, which was presumably an asteroid or comet fragment.

Peter B
2009-Jan-30, 01:51 PM
G'day Coliver

Where did you read that article? It sounds like it's based on the theory that covers the creation of the Moon more than 4 billion years ago. The theory is that early in the history of the Solar System, a planet about the size of Mars collided with the Earth. The collision threw up a huge amount of rocky material, most of which crashed back to the Earth, but some of which stayed in orbit and coalesced to form the Moon. However, the core of the impactor merged with the core of the Earth, giving the Earth a larger core than we might otherwise expect the Earth to have now.

Your own theory, however, doesn't really match with the evidence scientists have uncovered:

1. Life appeared on Earth a lot more than 10,000 years ago.

2. Evolution does not mean appearance or creation. Evolution means change over time. A meteor could cause evolution in an indirect sense, in that the impact could change a region's climate and thus affect which organisms survive, but it's unlikely that a meteor could create life.

3. It's possible, but unlikely, that a large object could have struck the Earth 10,000 years ago. Usually, if large objects strike the Earth, they leave detectable craters - think of the Chicxulub crater which can be detected even though it's about 65 million years old.

4. If an icy object struck the Earth, there's no way it could "merge" with the Earth's core.

coliver
2009-Jan-31, 01:36 AM
Im not sure about the 10,000 years? Could have been much longer. I just remember it was an event that scientists were saying they thought happened after the dinosaur extinction that led to new lifeforms and the change of fauna/flora on Earth. If you look at Earth its obviously been cooling off from much hotter state. I was just wondering if what made earth unique among planets was an event where a cold mass collided with a hot star and cooled it off?

Murphy
2009-Jan-31, 04:07 AM
Im not sure about the 10,000 years? Could have been much longer. I just remember it was an event that scientists were saying they thought happened after the dinosaur extinction that led to new lifeforms and the change of fauna/flora on Earth.

Sounds like you're talking about the cometary impact that caused the extinction of the Dinosaurs, it's called the K-T impact. Just look up Cretaceous–Tertiary extinction event on Wikipedia or elsewhere.

That impact (assuming it was the impact that caused the mass extinction, there's still some debate about it) did indeed cause major evolutionary changes to life on Earth, because the Dinosaurs were no longer the dominant type of lifeform and the Mammals and Birds replaced them.


If you look at Earth its obviously been cooling off from much hotter state. I was just wondering if what made earth unique among planets was an event where a cold mass collided with a hot star and cooled it off?

Eh, no it doesn't work like that, the Earth was once very hot (completely molten) but it was certainly never a star. The Earth has been hit by many things in its 4.5 billion years of history, it originally formed out of an orbiting gas and dust cloud that clumped into solid objects under gravity, then the objects hit each other a merged and became bigger objects and so on, until the Earth was left as the only object.

It is also now widely accepted that shortly after it formed, the Earth was hit by another "proto-planet" that was the size of Mars (it's been named Theia), this massive collision completely destroyed Theia and blasted off a lot of the outer layers of Earth, that material orbited the Earth and eventually formed into the Earth's Moon (just look for Giant impact hypothesis).

As for Icy things hitting the Earth, it has been theorised that most of the Earth's water came from Icy comets that constantly rained down on the early Earth, though I'm not sure if this theory has gained widespread acceptance yet.

As for a cold mass colliding with a hot mass, it wouldn't cool it down, in fact any collision between celestial bodies releases a vast amount of heat (i.e. millions of Nuclear bombs worth), so the resulting object would probably be significantly hotter than either of the previous two.

mugaliens
2009-Jan-31, 08:19 PM
Im not sure about the 10,000 years? Could have been much longer.

We have clear evidence of craters on Earth, including some pretty big ones, that are billions of years old. Anything impacting the Earth in the last 10,000 years that was larger than a train would have left some evidence.

PetersCreek
2009-Jan-31, 09:24 PM
Today seems to be the day for comments on/about religion. Let's keep it on the science, folks.

Murphy
2009-Feb-01, 12:28 AM
Huh? Who mentioned religion?

Peter B
2009-Feb-01, 12:42 AM
Im not sure about the 10,000 years? Could have been much longer. I just remember it was an event that scientists were saying they thought happened after the dinosaur extinction that led to new lifeforms and the change of fauna/flora on Earth. If you look at Earth its obviously been cooling off from much hotter state. I was just wondering if what made earth unique among planets was an event where a cold mass collided with a hot star and cooled it off?

The Earth's temperature has been pretty stable for the last 4-odd billion years. That's how long we've had oceans on the Earth, which means the temperature must have been below 100 degrees C all that time. In other words, by that time, the Earth's temperature had reached a stable equilibrium. What determines the Earth's temperature is things like the Sun, the Earth's albedo (reflectiveness) and the heat released from the Earth's core by the slow decay of radioactive elements there.

There's a theory the Earth was pretty much covered by ice in the late Pre-Cambrian period, about 650 million years ago, so back then the Earth was a fair bit colder than it is now, but there are also times between then and now when the Earth has been a bit warmer than now (though here we're talking about maybe 10 degrees warmer).

What makes the Earth unique among planets is a number of factors:

- It's the right distance from the Sun to be not too hot and not too cold;
- It has just the right amount of water to fill the oceans without sloshing too much onto the continents;
- It has a Moon which provides good tidal variation and stabilises its axial tilt; and
- It has a large planet (Jupiter) elsewhere in the Solar System which captures wandering comets and asteroids which might otherwise crash into the Earth.

There's probably a few other factors as well.