How the Flora Family of Asteroids Shaped the History of Life

How the Flora Family of Asteroids Shaped the History of Life

The solar system has asteroid/comet belts like no other known planetary system. The great majority of known planetary systems have had their comet/asteroid belts completely eradicated by the inward drift of their ice and gas giant planets. The remaining few known planetary systems have had no significant inward drift of ice and gas giant planets. This lack of significant drift has left these planetary systems with comet/asteroid belts that are hundreds to thousands of times larger than the solar system’s. As I wrote about in chapters 5 and 6 of my book Improbable Planet,1 only our solar system, out of more than 2,700 planetary systems discovered so far,2 has the just-right comet/asteroid belts to make advanced life possible.

The problem with planetary systems devoid of comets and asteroids is that there would be 1) no natural means to replace the atmosphere and oceans lost through the advanced-life-essential Moon-forming event, 2) no natural means to salt an Earth-twin planet with concentrated valuable metals, 3) no natural means to replace the very gradual erosion of water and other volatiles from an Earth-twin planet, and 4) no natural means to regularly remove whole ecosystems of life that no longer are capable of compensating for the host star’s increasing luminosity. The problem with planetary systems with comet/asteroid belts that are hundreds to thousands of times bigger than the solar system’s is that an Earth-twin planet in such a system would be so heavily bombarded by comets and asteroids as to make the existence of advanced life impossible. Again, see Improbable Planet for just how miraculously fine-tuned our solar system’s asteroid/comet belts are for the existence of advanced life and advanced civilization.

Our solar system has five belts of asteroids and comets.3 They are:

  1. the Main Belt (between Mars and Jupiter)
  2. the Centaurus Belt (between Jupiter and Neptune)
  3. the Scattered Belt (from Uranus to twenty billion miles from the Sun)
  4. the Kuiper Belt (from four to six billion miles from the Sun)
  5. the Oort Cloud (from ten billion to two trillion miles from the Sun)

For comparison, Jupiter, Uranus, and Neptune orbit 0.482, 1.782, and 2.791 billion miles from the Sun.

Even though the Main Belt is the smallest of the solar system’s asteroid/comet belts, because it is the closest one of the five belts to Earth it currently poses the greatest risk of a civilization-destroying or civilization-disrupting impact event. As I explained in Improbable Planet, thanks to the exquisitely fine-tuned dynamical history of the solar system’s original two gas giant planets and three ice giant planets, the inner part of the Main Belt was depleted.4 This depletion was critical for making the existence of human beings and their civilization possible.

Now, a new study5 reveals that the remaining innermost family of asteroids, the Flora Family, also possesses design features making possible our existence at this time in Earth’s history. Thanks to the Sloan Digital Sky Survey and the Wide-field Infrared Survey Explorer, more than 100,000 Main Belt asteroids are now known to exist. Of these 100,000+, only several thousand belong to the Flora Family. The new study employed eight different dynamical and observational tools to determine for the first time an accurate age for the formation of the Flora Family of asteroids. One of those tools involved the analysis of high-resolution images of the largest Flora Family asteroid, Gaspra, to determine its cratering history (see featured image). The age deduced from the eight tools = 1.5–1.6 billion years ago.

These dynamical and observational tools also reveal that Earth received the greatest number of large impactors from the Flora Family 100–300 million years after its formation. The Flora Family filled the near-Earth-orbit space with nearly 1,000 bodies greater than 1 kilometer in size. Within the first 300 million years after the formation of the Flora Family, “700–950 and 35–47 kilometer-sized asteroids struck the Earth and Moon respectively.”6 Today, only 35–50 kilometer-sized asteroids in the Flora Family remain that are even capable of entering near-Earth orbits.

At least four conclusions can be drawn from the new study that are relevant to the history of life on Earth.

  1. The dynamical history of the solar system’s ice and gas giants eliminated the inner part of the Main Belt, the most dangerous to life asteroids, before the origin of life on Earth.
  2. The innermost part of what remained of the Main Belt was more than 95% depleted by one billion years ago. This depletion occurred 400 million years before the appearance of the first animals on Earth.
  3. The early depletion of the Flora Family helps explain what paleontologists refer to as the Boring Billion, a reference to the period in Earth’s history 1.6–0.6 billion years ago during which no major new phyla of life appear. However, as I explained in Improbable Planet,7 the Boring Billion actually was not boring at all, in that several major geological and chemical events were preparing Earth’s surface for the entrance of animals and large plants.
  4. Enough members of the Flora Family survived the early depletion to explain the relatively recent impact events in Ontario, Canada and in eastern South Africa that are responsible for most of the high-quality nickel and gold ores that have been mined.

We have much to thank God for, including the way he designed the solar system’s five asteroid/comet belts. We now have several more reasons for the way God designed the innermost Main Belt asteroids, namely the Flora Family, for our benefit. This recent study of the Flora Family yields yet more proof that the more we study the realm of nature, the more evidence we will uncover for the supernatural handiwork of God.

  1. Hugh Ross, Improbable Planet: How Earth Became Humanity’s Home (Grand Rapids: Baker, 2016), 44–48, 57–60, 63–76.
  2. Exoplanet TEAM, The Extrasolar Planets Encyclopedia (April 20, 2017).
  3. Hugh Ross, “Thank God for the Solar System’s Asteroid Belts,” Today’s New Reason to Believe (blog), Reasons to Believe, January 9, 2014,
  4. Ross, Improbable Planet, 71.
  5. David Vokrouhlicky, William F. Bottke, and David Nesvorny, “Forming the Flora Family: Implications for the Near-Earth Asteroid Population and Large Terrestrial Planet Impactors,” Astronomical Journal 153 (April 2017): id. 172, doi:10.3847/1538-3881/aa64dc.
  6. Vokrouhilicky, Bottke, and Nesvorny, “Forming the Flora Family,” page 1 of their paper.
  7. Ross, Improbable Planet, 127–142.