Apart from the Sun, planets and moons, the solar system contains a large number of space rocks, fragments that are in most cases remnants of the formation of the inner planets, including Earth.
Meteorites and comets are much more than just extraterrestrial rocks.
They have allowed us to estimate the age of the Earth, have provided large quantities of water to form the oceans and have influenced the development and evolution of living beings, including us humans.
1. The age of the Earth
About 4.5 billion years ago, Theia, a Mars-sized planet, collided with what was then the proto-Earth. The impact changed the planet’s composition and led to the formation of the Moon.
For the first few 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 uncertain.
However, it has been possible to estimate it by knowing the age of primitive meteorites and the oldest rocks that we have managed to find and date.
The oldest minerals that have been accurately dated on Earth are small zircon grains found in Western Australia.
The oldest is 4.404 billion years old. However, inclusions rich in calcium and aluminum found in primitive meteorites (carbonaceous chondrites), which yielded an oldest age of 4.567 billion years, the age of the solar system.
Thus, the best estimate is that the Earth was formed approximately 4.543 billion years ago.
2. Basic components for the development of life
One of the most widely accepted theories about the origin of life suggests that simple organic compounds formed in space and reached Earth. aboard meteorites and other celestial bodies.
During the period known as the Late Heavy Bombardment, which took place between 4.1 and 3.8 billion years ago, numerous impacts occurred. The Earth’s surface was then partially solid.
In that bombardment, amino acids, hydrocarbons and other carbon-based molecules arrived in carbonaceous chondritesprimitive meteorites remnants of the early solar system and comets.
Once the early Earth was enriched with these organic molecules, according to some hypotheses, the chemical evolution and eventually, life emerged.
The earliest evidence of life They are microorganisms from approximately 3.8 billion yearsrelatively soon after the late heavy bombardment.
3. How the oceans originated
Large amounts of extraterrestrial water also arrived during the Late Heavy Bombardment. And all indications are that meteorites and comets played a role. crucial role in the formation of the Earth’s oceans and atmosphere.
In turn, during the Hadean Eon (from the formation of the Earth until about 4 billion years ago) volcanoes released gases from the interior of the planet.
Water vapor, carbon dioxide, methane, ammonia, nitrogen and sulfur formed the protoatmosphere.
And then came the first rain. It occurred once the temperature on the Earth’s surface dropped below the boiling point of water, thus allowing the formation of a primordial ocean.
Yes, the water we drink today is, at least in part, of extraterrestrial origin.
4. Those who disappeared
The geological record proves the undeniable impact that meteorites have had 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 the 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, is explained by multiple impacts (such as the Alamo craters in the United States, Siljan in Sweden and Woodleigh in Australia), climate change, decreased oxygen in the oceans and volcanic activity.
5. The deep mantle and the Earth’s core
We have access to rock samples from Earth’s crust and upper mantle, but we will not be able to obtain direct samples from the deep mantle or solid core.
However, we can know what is deep inside by studying the pallasites and metallic meteoritesrocks from differentiated asteroids, those that, like the Earth, have a mantle and a core.
Pallasites are rare and contain crystals of olivine, a magnesium-iron silicate, cemented together by nickel-iron alloys. These rocks formed at the boundary between the mantle and the core of differentiated asteroids.
Metallic or iron meteorites are composed primarily of nickel-iron alloys, such as kamacite and taenite. They represent fragments of the cores of differentiated asteroids, rocks equivalent to the core of our own planet.
6. Huge deposits of gold and nickel
The collision of ancient meteorites has had an indirect and lasting impact on our society by influencing the availability of gold and nickel.
The Witwatersrand rocks in South Africa contain the largest known gold reserves in the world. This wealth would not have been possible without the impact of Vredefortwhich produced the largest known meteorite crater on Earth, formed approximately 2.023 billion years ago.
The impact preserved these gold deposits from erosion by covering the region with ejecta, obscuring the mineralized layers beneath.
The third largest known impact crater on Earth is the Sudbury Basin, Canadaformed 1,849 million years ago.
The basin is home to huge deposits of nickelas the impact disturbed the Earth’s crust, partially melting it and allowing magma to rise from the mantle. This led to the accumulation of Nickel, copper, palladium, platinum and other metalsproducing one of the richest mining districts on the planet.
*Francisco José Testa is Professor of Earth Sciences (Mineralogy, Petrology and Geochemistry), University of Tasmania, Australia. The author would like to thank Prof. Noel C. White, University of Tasmania, for his valuable comments on this article.
*This article was first published on The Conversation and is reproduced here under a creative commons license. Click here to read the article in its original version.
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