An asteroid may have wiped out the dinosaurs 65 million years ago, but an earlier one probably allowed the rise of the giant creatures, who dominated the planet for 135 million years. After their demise, mammals took over and eventually evolved into humans, so our domination was caused by an asteroid as well. Will asteroids also bring about the end of human civilization?

Experts have decided that a huge impact wiped out most of the plants and crocodile-type creatures that ruled the world during the Triassic era. “Our research adds to the speculation that there was a comet or asteroid impact about 200 million years ago, followed relatively quickly by the rising dominance of dinosaur populations of the Jurassic period,” says Dennis Kent, a geology professor at Rutgers University in New Jersey. “Dinosaurs went on to dominate for the next 135 million years.”

Lacking competition, dinosaurs were free to evolve into bigger and bigger versions. “They replaced a whole suite of other kinds of carnivores that, for the most part, are remotely related to living crocodilians,” says Paul Olsen of Columbia University in New York. Looking at footprints and fossilized bones from nearly 80 different sites, Olsen’s team concluded that it only took about 50,000 years for dinosaurs to start growing really big.

Before the Jurassic, the biggest dinosaur around was probably something likeplateosaurus, a long-necked, two-legged vegetarian about 20 feet long. Afterwards, giant carnivores such as tyrannosaurus reached lengths of 41 feet and more. Argentina’s giganotosaurus was more than 45 feet long. “You want to get as large as you can so you can eat what you want,” Olsen says. Living examples include the Komodo monitor lizards of Indonesia and a similar creature that lived in Australia until humans arrived and wiped them out.

Scientists once thought it took millions of years for dinosaurs to get so large, but Olsen says the evidence points to a quick explosion of size and diversity among dinosaurs. Humans haven?t grown much in size?our evolution has been concentrated on developing big brains.

Other fossil evidence shows plants have changed too. A huge asteroid hit would have sent up a plume of dust and smoke that obscured the sun for centuries, killing off plants and the animals that depended on them.

Most scientists agree about the asteroid hit, but they haven?t yet located the crater, although there are candidates in Canada and Australia. Olsen points out it took 15 years to find a 65 million-year-old crater in the Yucatan and says, “We don’t actually have an impact structure yet.”

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The first meteorite from Mercury has been found in the Moroccan Sahara. It clearly has a molten past and was formed from lighter materials than most meteorites, so it was probably once been part of a much larger planetary body.

It was originally thought to be from the asteroid Vesta, but NWA 011 has an oxygen isotope ratio that indicates it came from a body larger than an asteroid. Now researchers think it?s the first known meteorite from our Solar System’s innermost planet, Mercury.

Rocks blasted off Mercury by a large asteroid would have a difficult journey to reach the Earth, but it?s not impossible. Such rocks would be extremely rare on Earth.

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