Ebb and Flow of Life Itself Linked to Space

For decades it has been theorized that an impact from space caused the death of the dinosaurs 65 million years ago. At that time, the fossil record shows a mass extinction of a good percentage of most large animals. The suspected crater has even been found in the Yucatan Peninsula. Now, scientists are looking at other mass extinctions in Earth's past to see if they too could have a cosmic link.

One of the latest in these investigations is a mass extinction which took place about 380 million years ago and wiped out over forty percent of marine animals. At this stage in Earth's past, most life was aquatic. And just after so many life forms disappeared from the fossil record, many new forms of life appeared within a short timeframe. This extinction may well be connected with an apparent impact which took place in the Moroccan desert.

Unlike the crater in the Yucatan, the site in Morocco is not so obvious, but there is still strong evidence that an impact took place. Geologists look at the surrounding rock for shocked quartz and other deformations in native rock. The presence of the element Iridium is the strongest evidence for an impact. Iridium is relatively rare on Earth, but it is common in asteroids and comets. This means that if geologists find a higher-then-normal concentration of iridium in the rock layers, there is a very good chance an impact did occur. Using age dating techniques, scientists can determine just how long ago the impact took place. In this case, the evidence shows an impact 380 million years ago, the same time as when the mass extinction took place.

Another mass extinction being looked at is one which occurred 250 million years ago and may be related to the rise of the dinosaurs. As well as causing their extinction, some scientists now believe that an impact played a role in the dinosaurs ascent to top animals. The dinosaurs took over the role of dominant life form about 250 million years ago, and not surprisingly, there is evidence of an impact at about that same time.

A study last June, also reported in Science, found extraterrestrial gases trapped inside special molecules, known as fullerenes, in rock layers corresponding to an earlier and greater mass extinction, which occurred 251 million years ago. This event wiped out 75 percent of all species and was likely a first step in allowing dinosaurs to enter the scene.

Because of mass extinction, there was little competition for the dinosaurs. and within 100,000 years (a very short time for evolution,) they evolved to become huge and diverse animals that ruled the entire planet for over 145 million years!

Finding evidence for an impact 250 million years ago is no small task. The Earth was very different back then. All of the continents were squashed together in one land mass called Pangea. To find iridium, the scientists must find exposed areas of 250 million year old sedimentary rock. Much of the evidence was collected in what are now parts of New Jersey and Pennsylvania, along with other dig sites dotting the eastern United States.

Looking at the fossil records of life on Earth, there is evidence to show that every so often something causes mass extinction's, where great numbers of plant and animal species disappear to be replaced by new ones. The fossil records is a sort of family tree of all life on Earth. The biggest mystery had been what could have caused these mass extinctions. Evidence is now pointing toward asteroids and comets. Such impacts may have played a major role in the evolution of life on Earth.

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