"Why don't we see new species emerging now?" Charles Darwin faced this question nearly 150 years ago when he proposed the theory of evolution. His answer–all Earth's habitats are full.
Whether or not his reply made sense then, it certainly doesn't hold up today. During the human era thousands of extinctions have emptied multiple environmental niches, and these habitats remain unfilled by new genera.
Darwin was right about one thing, however. He recognized the reality of both extinction events and speciation events in the fossil record. Recent research has amplified the reasons for, as well as the benefits of, the extinction events.
Astronomers recognize that conditions in the solar system have changed dramatically since life began. For example, the sun's brightness initially decreased and then began a steady, ongoing increase, and Earth's rotation rate has slowed. Such changes impact life.
When certain species can no longer help compensate for such changes,1 those species must be removed to make way for others that can. But if this removal were random, total ecological collapse could occur. At the just-right moment, the outdated species–usually a whole cluster of species that serve together in a particular ecological role–must be taken away and quickly replaced.
These targeted extinctions require events that selectively, and with precise timing, remove the outdated species and their ecological support system. New data shows that asteroid and comet collisions ideally provide for such extinctions.2 Earth happens to be optimally located within the solar system's layout to receive the just-right number and kind of extinction-causing impacts. If Earth were much nearer to Mars' orbit, asteroid and comet collisions would be too frequent and too extreme. If Earth were much nearer to Venus' orbit, collisions would occur too seldom and be too weak to bring about the necessary extinctions.
Prior to these findings, astronomers defined "habitable" zones around stars by two criteria:
1) the distance range where surface liquid water can be present on a planet and 2) the distance range in which the just-right quantity and kind of ultraviolet radiation can reach the planet's surface.
Now a third criterion must be added: a just-right death zone, the distance range in which the just-right frequency and intensity of asteroid and comet collisions can occur.
For life to be sustained long-term, a planet must simultaneously reside in all three zones–a very restrictive region indeed.
This analysis supports RTB's message that the more scientists learn, the more evidence accumulates for the supernatural, super-intelligent design of the cosmos and Earth for humanity's benefit. The psalmist anticipated such work by 3,000 years when he worshipped God in these words:
These [creatures] all look to you to give them their food at the proper time . . . when you take away their breath, they die and return to the dust. When you send your Spirit, they are created, and you renew the face of the earth.3