Chemistry Shows Dinosaur Killing Asteroid Wasn't From Around Here

Using advanced technology, scientists determine Earth's most famous asteroid came from beyond our solar system

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We humans rule the world now, but a different group of animals ruled long before us — the Dinosaurs. We Homo sapiens have been around for a few hundred thousand years, but the dinosaurs ruled for 140 million years. They likely would have reigned for millions more, but an asteroid smashing into Earth around 65 million years ago abruptly ended the dinosaur dynasty.

If there’s one thing we humans love, it’s a good story — and the dinosaurs have a great one. We’ve been piecing it together bit by bit ever since the first dinosaur fossil was documented in 1677. But despite how many species paleontologists identify or what we learn about them, it’s their demise that captures our imagination most. Now, researchers have more information about the asteroid responsible.

Chemistry of Asteroids

Before we get to the new research, let’s review some basic science. Many objects are flying around space, including rocky asteroids and icy comets. Then there are meteors and meteorites, which are smaller chunks of either asteroids or comets that sometimes create shooting stars in the night sky as they burn in Earth’s atmosphere. But today, asteroids are the star (metaphorically speaking).

As Jupiter formed in our early solar system, its gravity ended the formation of planetary bodies in our little corner of space. Any remaining smaller bodies floating around collided, fragmenting into the asteroids we see today. Most of these asteroids orbit our Sun between Jupiter and Mars in the asteroid belt.

Composition

While all asteroids are rocky, they come in many shapes and sizes, and each contains chemical compositions that scientists can use to determine where in space they came from. So far, three broad categories of asteroid chemical compositions exist: C-, S-, and M- types.

1. C-type, or chondrite, asteroids are the most common, accounting for roughly 86 percent of all meteorite falls. They seem to consist of clay and silicate rock. There are many varieties of chondrite, with differences in mineralogy that tell scientists the type of asteroid the meteorite came from. Still, they are some of the oldest objects in the solar system.

2. S-types, or stony asteroids, are a mixture of silicate material and nickel-iron and form in the inner solar system. This group is the second most common type of asteroid, accounting for about 17 percent of asteroids in the solar system. They dominate the asteroid belt but become more rare farther out.

3. M-types, or metallic, asteroids are mostly made of metals like nickel and iron, but their compositional differences depend on how close they were to the Sun when they formed. The Sun’s high temperatures can melt the metals in M-type asteroids, so they sink to the center, forcing volcanic lava (which forms basaltic rock) to its surface.

Regardless of material, most asteroids in our solar system are in stable orbits, so there is nothing we need to worry about. But sometimes, Jupiter’s massive gravity can pull asteroids from their orbits and fling them in all directions across space, including into the orbits of other planets.

And, sometimes, stray asteroid fragments are hurled right into planets, including Earth, remaining intact as they blow through the atmosphere and slam into the planet’s surface, forever changing the geological history of planets and the evolution of Life on Earth.

Just ask the dinosaurs.

Asteroid > Dinosaurs

The Chicxulub crater, named after a nearby town, is over 93 miles (150 kilometers) wide and was first discovered in the late 1970s by a UC Berkley physicist and Nobel laureate Luis Alvarez and his son Walter, a UC Berkeley geologist.

The crater, the second largest on Earth, was made by an asteroid estimated to be about 6 to 9 miles (10 to 15 kilometers) across that was traveling about 15.5 miles (almost 25 kilometers) per second when it slammed into the coast of today’s Yucatán peninsula in Mexico about 66 million years ago (mya).

According to NASA, the Chicxulub impact was about 10,000 times the global nuclear arsenal. It would have plunged the world into an immediate nuclear winter, including a megatsunami with mile-high waves, wiping out nearly all the dinosaurs and about three-quarters of Earth’s plant and animal species.

When the asteroid hit, it vaporized massive quantities of earth rock, causing tiny dust particles to fly into Earth’s stratosphere. These particles blocked sunlight and halted photosynthetic activities for years.

Over time, the dust particles from the impact fell to the ground, forming a layer of sediment around the globe. This layer marks the boundary between the Cretaceous (145 to 66 mya) and Paleogene (66 to 23 mya) periods. It also contains high levels of iridium, a metal from the asteroid that is extremely rare in earth rocks.

Now, a similar metal called ruthenium was discovered in the same boundary layer. Like iridium, ruthenium is rare in Earth’s crust but found in asteroids and meteorites, and its existence in the boundary layer gives experts a clue as to where the dinosaur-killing asteroid came from.