What Animals Were Involved in the Cambrian Explosion

No one disputes that a huge diversity of large animals emerged with alacrity between 600 and 500 million years ago. The event itself took place in the sea, for the land areas of the time were largely barren except for lichens and perhaps a few low plants there were no trees, no shrubs, no stemmed plants at all. Because of the lack of rooted vegetation, little soil would cling to the land surfaces. In the shallow seas and waterways, however, life was plentiful (though clearly different from that...

Risk and Complexity

Can we discern a relationship between the complexity of life and its risk of succumbing to mass extinction Recent evidence suggests that as organisms become more complex, their risk of undergoing extinction increases. As an organism's complexity increases, so too does its fragility, hence increasing complexity in most cases narrows the environmental tolerances of a living organism. Any bacterium can withstand the rigors of outer space (at least for a short period of time), but no animal can. As...

Lunar Tides

A second benefit of Earth's large moon is tides, which are due to gravitational effects of both the sun and the Moon. The pull of these two bodies produces bulges in the ocean pointing both toward and away from the Moon and the sun. The complexity of Earth's present tidal effects is well illustrated by the tidal charts cherished by clam diggers, anglers, and sailors. The daily variations seen in the charts are caused by the interplay of both lunar and solar tides. Both the Moon and the sun...

An Ancient Dichotomy

The gulf between the complexity of a bacterium and the complexity of even the simplest multicellular animal, such as a flatworm like Planaria, is immense. The number of genes in a bacterium can be measured in the thousands, whereas the genes in a large animal number in the tens of thousands. To illustrate this, we can liken a bacterium to a simple toy wooden sailboat. With only three or four very tough parts, the toy boat is virtually indestructible, just as a bacterium is impervious to most...

Habitable Zones of the Universe

Rendezvous with Rama. London Gollancz. Cloud, P. 1987. Oasis in space. New York Norton. De Duve, C. 1995. Vital Dust. New York Basic Books. Dole, S. 1964. Habitable planets for man. New York Blaisdell. Doolittle, W. F. 1999. Phylogenetic classification and the Universal Tree. Science 284 2124-2128. Doyle, L. R. 1996. Circumstellar habitable zones, Proceedings of the First International Conference. Menlo Park, CA Travis House. Forget, F., and Pierrehumbert, G. D. 1997....

Surprising Importance of Plate Tectonics

Imagine that we have a spacecraft capable of swiftly taking us to each planet in the solar system. Our goal on this voyage is to try to determine what features of Earth are essential to animal life. On our voyage, therefore, we are looking for some clue to why animal life has been able to survive on Earth for a time period approaching a billion years. What are those factors that have fostered diversity on Earth We begin our celestial survey with Mercury, a cratered world of great heat on the...

Mass Extinctions and the Rare Earth Hypothesis

Asaro, F. and Michel, H. 1980. Extra-terrestrial cause for the Cretaceous-Tertiary extinction. Science 208 1094-1108. Alvarez, W. 1997. T. Rex and the Crater of Doom. Princeton, NJ Princeton University Press. Annis, J. 1999. Placing a limit on star-fed Kardashev type III civilisations. Journal of the British Interplanetary Society 52 33-36. Bourgeois, J. 1994. Tsunami deposits and the K T boundary A sedimentolo-gist's perspective. Lunar Planetary Institute Cont. 825 16....

The History of Mass Extinctions on Earth Ten Events

Paleontologists have discovered many mass extinction events that occurred since the Cambrian Explosion (that is, in the past 540 million years). Yet other mass extinction events of earlier times are largely unknown to us, because they occurred when organisms rarely made skeletal hard parts and thus rarely became fossils. Perhaps the long period of Earth history prior to the advent of skeletons was punctuated by enormous global catastrophes that decimated the biota of our planet mass extinctions...

Creation of the Elements

Although we understandably date Earth's history from the origin of the planet, a considerable prehistory preceded Earth's formation. one of the most important aspects of this period was the origin of the chemical elements. The elements are the building blocks of both planets and life. Consider that in a sort of cosmic reincarnation, every atom in our bodies resided inside several different stars before the formation of our sun and has been part of perhaps millions of different organisms since...

How Do Plate Tectonics Operate At Luna

Without the Moon there would be no moonbeams, no month, no lunacy, no Apollo program, less poetry, and a world where every night was dark and gloomy. Without the Moon it is also likely that no birds, redwoods, whales, trilobites, or other advanced life would ever have graced Earth. Although there are dozens of moons in the solar system, the familiar ghostly white moon that illuminates our night sky is highly unusual, and its presence appears to have played a surprisingly important role in the...

Lovers of the Extreme

The environments around the deep-ocean volcanic rifts can be described with a single word extreme. Extreme heat, extreme cold, extreme pressure, darkness and toxic-waste waters are conditions seemingly inhospitable to every living thing. Yet over the past two decades, oceanographers and biologists who have braved the perils of the long trip to this depth in their small submarines have made stunning discoveries. The finding of bizarre tubeworms and clams was completely unexpected, but even this...

Plate Tectonics as Global Thermostat

Over and over again we come back to to a common theme the importance of liquid water. For animal life based on DNA to exist and evolve, water must be present and abundant on a planet's surface. Even on the water-rich Earth today, slight differences in water content obviously affect life. In desert regions there is little life in rainforests at the same latitude, life teems in abundance. For complex life to be attained (and then maintained), a planet's water supply (1) must be large enough to...

Lifes First Appearance on Earth

E. 1984. Archaean plate tectonics revisited. 1. Heat flow, spreading rate, and the age of subducting oceanic lithosphere and their effects on the origin and evolution of continents. Tectonics 3 429-448. Bada, J. L. Bigham, C. and Miller, S. L. 1994. Impact melting of frozen oceans on the early Earth Implications for the origin of life. Proceedings of the National Academy of Sciences USA 91 1248-1250. Barns, S. M. Fundyga, R. E. Jeffries, M. W. and Pace, N. R....