6 Things We Learned About Earth From Meteorites and Comets

Besides the Sun, its planets and their moons, our solar system has large amounts of space rocks – fragments left over from the formation of the inner planets.

A large concentration of asteroids forms a vast ring around our Sun, orbiting between Mars and Jupiter. It is aptly called the main asteroid beltComets are icy bodies composed of dust and rock that originate from even more distant regions, such as the Kuiper Belt, beyond Neptune, and the Oort debris cloud surrounding the solar system.

Extraterrestrial rocks come in a wide variety of sizes. In general, asteroids are space rocks larger than one meter in diameter, while smaller ones (from two millimeters to one meter in diameter) are called meteoroids.

Whatever their origin, these foreign rocks, once they reach the surface of the Earth, are called meteorites. But they are much more than just rocks that come from very, very far away.

They have helped us estimate the age of our planet and changed the course of evolution on several occasions. Here are six major ways meteorites and comets have contributed to Earth’s history or our knowledge of it.

1. The age of our planet

About 4.5 billion years ago, a Mars-sized planet collided with proto-Earth, changing the composition of our planet and forming our Moon.

During its first tens of millions of years, Earth was mostly molten. It was too hot to form solid minerals and rocks, so the exact age of our planet remains unknown. But we do know that it is somewhere between the age measured from meteorites and the age of the oldest rocks we have been able to find and date.

The oldest minerals that have been reliably dated on Earth are Tiny zircon grains discovered in Western Australia. The oldest is 4.4 billion years old. However, scientists have also dated calcium and aluminum particles found in meteorites, which gave an older age of 4.56 billion years – the age of our solar system.

So, thanks in part to the oldest age provided by a meteorite, our best estimate is that the Earth formed about 4.54 billion years ago.

2. The building blocks of life

The most plausible theory about the beginning of life on Earth is based on simple organic compounds that formed in space and were brought to Earth by meteorites and other celestial bodies.

During the Late heavy bombinga period between 4.1 and 3.8 billion years ago, when more impact events struck our planet, the Earth’s surface was partially solid.

Amino acids, hydrocarbons and other carbon-based molecules arrived on our planet in carbonaceous chondrites (primitive meteorites, remains of the primitive solar system) and comets.

Once the primitive Earth was enriched with these organic molecules, chemical evolution followed. Finally, life appeared on our planet. The first evidence is a Microbial life 3.8 billion years agoshortly after the last massive bombing.

Regardless of how life arose, all theories agree that there must have been a primitive ocean – or pools of water – that allowed primitive life on Earth to develop.

3. How we got our oceans

Meteorites and comets have also played a major role in the formation of the Earth’s oceans and atmosphere. Large quantities of water have been delivered to our planet during the last heavy bombing.

Additionally, water has been released from the Earth’s interior by volcanic activity during the Hadean Aeonthe first eon in the history of our planet.

Water vapor, along with other gases such as carbon dioxide, methane, ammonia, nitrogen, and sulfur, formed the proto-atmosphere. Rain began to fall when the temperature dropped below the boiling point of water, forming our early ocean.

Yes, the water we drink today is at least partly of extraterrestrial origin.

4. Change the course of evolution

The extinction of the dinosaurs occurred around 66 million years agoIt is linked to the second largest known meteorite impact on Earth, the Chicxulub crater, deep in Mexico.

On the other hand, the Late Devonian Extinction About 380 to 360 million years ago, it is not possible to explain the single impact. Several factors have been proposed as potential causes, including multiple impactsclimate change, oxygen depletion (anoxia) in the oceans and volcanic activity.

At several times throughout Earth’s history, impact events have influenced the survival and evolution of life on our planet.

5. Sampling of the deep mantle and Earth’s core

Scientists use a combination of methods to understand the internal structure of the Earth: crust, mantle, core and their subdivisions. The most important of these is seismology, which studies the propagation of seismic waves generated by earthquakes or artificial sources. through the interior of the Earth.

We have access to samples of rocks from the Earth’s crust and upper mantle, but we will never be able to take samples from the deep mantle or solid core. Even if we had the technology, it would be astronomically expensive, and going to such depths involves extreme pressures and temperatures.

Since direct sampling is impossible, scientists resort to indirect methods.

Pallasites and metallic meteorites are rocks from differentiated asteroids, that is, those with a mantle and a core. These space rocks are what will allow us to sample the deepest parts of our own planet the most. They help us understand its composition.

Pallasites are rare and contain a silicate mineral called olivine embedded in nickel-iron alloys. Pallasites are thought to form at the boundary between the core and mantle-like regions of differentiated asteroids.

Metallic or ferrous meteorites are mainly composed of nickel-iron alloys, kamacite and taenite. They are the fragments of the core of differentiated asteroids, giving us clues about the core of our own planet.

6. Meteorite impacts have given us huge deposits of gold and nickel

The rocks of the Witwatersrand in South Africa are home to the the largest known gold reserves in the worldThis would not be the case without the Vredefort impact crater – the largest known impact structure on Earth – formed around 2.02 billion years ago.

The impact saved these gold deposits from erosion by covering the entire area with ejected material, obscuring the ore-bearing layers below. If an ore deposit erodes, the material will disperse and its extraction would be uneconomic.

The Witwatersrand is the world’s largest gold producing region. This means that the impact of an ancient meteorite has had an indirect and lasting impact on our society through the availability of this precious metal.

But this is not the only event of this type. The third largest known impact crater on Earth is the Sudbury Basin In Canada, this deposit formed 1.85 billion years ago. It contains giant nickel deposits because the impact disrupted the Earth’s crust, partially melting it and allowing magma from the mantle to rise.

This led to the accumulation of nickel, copper, palladium, platinum and other metals, producing one of the richest mining districts on the planet.

The author would like to thank Professor Noel C. White, University of Tasmania, for his helpful comments on this article.