Six Discoveries About Earth That We Owe to Meteorites and Comets
In addition to the Sun, planets and moons, the Solar System contains a large number of space rocks, fragments that in most cases are remnants of the formation of the inner planets, including the Earth.
Meteorites and comets are much more than just extraterrestrial rocks. They have allowed us to estimate the age of the Earth, provided large amounts of water to form the oceans, and influenced the development and evolution of living things, including us humans.
1. The Age of the Earth
About 4.5 billion years ago, Theia, a planet the size of Mars, collided with what was then called the proto-Earth. The impact changed the planet’s composition and led to the formation of the Moon.
For the first tens of millions of years, the Earth was in a predominantly molten state. In this environment of extreme temperatures, the formation of minerals and rocks was impossible, so the exact age of our planet is unknown. However, it was possible to estimate it, knowing the age of primitive meteorites and the oldest rocks that we were able to find and date.
The oldest minerals accurately dated on Earth are small grains of zircon found in Western Australia. The oldest is 4.404 million years old. However, calcium- and aluminum-rich inclusions found in primitive meteorites (carbonaceous chondrites) have also been dated, giving an even older age of 4.567 million years, the age of the solar system.
Thus, the best estimate is that the Earth formed approximately 4.543 million years ago.
Shiny Things/Flickr, CC BY-NC
2. The main components of life development
One of the most common theories of the origin of life suggests that simple organic compounds formed in space and arrived on Earth aboard meteorites and other celestial bodies.
During a period known as the Late Heavy Bombardment, which occurred between 4.1 and 3.8 billion years ago, there were numerous impacts. The Earth’s surface was then partially solid.
This bombardment injected amino acids, hydrocarbons, and other carbon molecules into carbonaceous chondrites, primitive meteorites left over from the early solar system, and comets.
According to some hypotheses, once the early Earth was enriched with these organic molecules, chemical evolution began and, eventually, life arose.
The earliest evidence of life is microorganisms, which appeared about 3.8 billion years ago, relatively soon after the Late Intensive Bombardment.
Francisco Testa/From the author’s personal collection.
3. How the oceans were formed
During the last intense bombardment, large quantities of extraterrestrial water also arrived. And all indications are that meteorites and comets played a decisive role in the formation of the Earth’s oceans and atmosphere.
In turn, during the Hadic eon (from the formation of the Earth until about 4 billion years ago), volcanoes emitted gases from the bowels of the planet.
Water vapor, carbon dioxide, methane, ammonia, nitrogen and sulfur formed the proto-atmosphere.
And the first rain fell. This happened when the temperature on the Earth’s surface dropped below the boiling point of water, allowing the formation of the primordial ocean.
Yes, the water we drink today is, at least in part, of extraterrestrial origin.
4. Those who disappeared
Geological evidence proves the undeniable influence of meteorites on the survival and evolution of life on our planet.
The extinction of the dinosaurs occurred about 66 million years ago. Their disappearance is linked to the impact of a meteorite that formed the Chicxulub crater, the second largest known impact on Earth, buried deep in Mexico.
In contrast, the Late Devonian extinction, which occurred between 380 and 360 million years ago, has been attributed to multiple impacts (such as the Alamo craters in the United States, Siljan in Sweden, and Woodley in Australia), climate change, deoxygenation of the oceans, and volcanic activity.
Wikimedia Commons, CC BY
5. The deep mantle and core of the Earth.
We have access to samples of rocks from the Earth’s crust and upper mantle, but we won’t be able to get direct samples of the deep mantle or the solid core. We can, however, learn what’s deep inside by studying pallasites and metallic meteorites, rocks from individual asteroids that, like Earth, have a mantle and core.
Francisco Testa/From the author’s personal collection.
Pallasites are rare and contain crystals of olivine, a magnesium-iron silicate cemented by nickel-iron alloys. These rocks formed at the mantle-core boundary of individual asteroids.
Metallic, or iron, meteorites are mostly nickel-iron alloys such as kamacite and taenite. They are fragments of differentiated asteroid cores, rocks equivalent to our own planet’s core.
Francisco Testa/From the author’s personal collection.
6. Huge deposits of gold and nickel
The ancient meteorite impacts had an indirect and lasting impact on our society by affecting the availability of gold and nickel.
The rocks of the Witwatersrand in South Africa contain the largest known gold reserves in the world. Such wealth would not have been possible without the Vredefort impact, which created the largest known meteorite crater on Earth, formed approximately 2,023 million years ago.
The impact protected these gold deposits from erosion by covering the region with ejecta, hiding the mineralized layers underneath.
The third largest known impact crater on Earth is the Sudbury Basin in Canada, which formed 1,849 million years ago. The basin contains huge deposits of nickel because the impact disrupted the Earth’s crust, partially melting it and allowing magma to rise from the mantle. This led to a buildup of nickel, copper, palladium, platinum and other metals, creating one of the richest mining areas on the planet.
The author would like to thank Prof. Noel K. White, University of Tasmania, for helpful comments on this article.