If you look back to the hazy enough prehistory, forgotten world, the making strange things.
Like beaten surface of the Moon, our own planet is covered by craters: scar heritage & # 39; & # 39 million; year & # 39; brutal impacts and asteroids indelible. What is strange, though, once you look back about 300 million years, evidence & # 39; this attack seems almost has disappeared.
For a long time, scientists assumed that the comparative rarity of impact craters that go beyond 300 million years ago Earth was linked to erosion; environmental processes such as weather or tektonika activity were b & # 39; some way removed the slate clean, and created what is known as & # 39; bias & # 39; Preservation & # 39; in the scientific record.
Not so, according to a new study, which suggests a simpler reason for invisible asteroids.
It's not that our terrestrial record & # 39; impacts & # 39; the asteroid ended after the fact. Rather, there was not as asteroids hitting us – or the Moon, for that matter – way back when.
Since then, however, we were caught in & # 39; epic increased activity & # 39; the asteroid, where two to three times the number of & # 39; rain space rocks on the Earth and its satellite reliable.
"Our research provides evidence for a dramatic change in the rate of & # 39; asteroid impacts both on Earth and on the Moon that occurred at the end of Paleozoika era", explains planetary scientist Sara Mazrouei from the University & # 39; Toronto, the first author & # 39; a new paper about the discovery.
"The implication is that by that time we have been in & # 39; period & # 39; relatively high rate of & # 39; impacts & # 39; the asteroid which is 2.6 times higher than it was before 290 million years ago . "
To reach this finding, researchers Mazrouei and colleagues analyzed data from the Lunar Orbiter Lunar Reconnaissance (LRO) NASA, space probe was orbitalment examine the Moon for nearly a decade.
One of the tools for this monitoring is called a diviner – thermal radiometer can & # 39; feels the heat of things on the lunar surface.
Because of this, it is able to date the b & # 39; effectively the age of craters on the Moon, by measuring the heat collecting rocks around smaller craters.
By the time the aging eminently, those larger rocks, called ejecta, milling & # 39; below in moundust dust cooler (due to the constant barrage of & # 39; meteor mini scale & # 39; time & # 39; & # 39 million; year).
Thanks to the LRO, this difference can & # 39; new observed between the powers of the two heat seized substances – known as thermal inertia – provides a way to measure how long those vast craters all over the Moon.
"Simple analogy to the concept of & # 39; thermal inertia is the rocks and sand at the beach", explains Mazrouei 2007 The Conversation.
"During the day both the rock great and the sand is hot. However, as the sun comes, the sand cool. The rock great to have a higher thermal inertia, however, remains & # 39; hot for longer. "
In their study, the team used this distinction to assess the age of 111 craters impact on the Moon smaller than a billion years.
What they found is that the vast majority of & # 39; those giant pockmarks were produced in the last 290 million years – an incredible replication of the prevalence of & # 39; comparisons in the last 300 million years or so of the World (and lack of & # 39; & # 39 comparative existence; impacts before).
"The Moon is like a time capsule, and help us understand the Earth," says one of the researchers, the planetary scientist William Bottke of the Institute of Southeast Asian Research.
"We found that the Moon had a similar history & # 39; bombing, which meant the response to the rate of & # 39; the impact of the World was thoroughly protects everyone in the face."
But if the Earth and the Moon began to be affected by a surge in local asteroids around 290 million years ago, which force issued this barrage?
Nobody really knows, but the researchers suggest crash or breakdown in asteroid belt located between the orbits of & # 39; Mars and Jupiter could & # 39; Waste flying around space in our direction.
Such an event can & # 39; produces "increases & # 39; long life in the flow of & # 39; impact as the fragments are driven way to escape routes from non-gravity forces", researchers explain in their paper.
"Models & # 39; evolution & # 39; the asteroid suggest that the contribution of & # 39; the impactor & # 39; size kilometers from major disruptions between the parents and the body would reach the level their again in a few tens of & # 39; million & # 39; years of the event (s) & # 39; rubble, in the wake of & # 39; maybe doing bodies decreases after hundreds of millions of years . "
If true, we can move towards the end of the wave phase. Or we can be well in the middle of a storm, or still in its infancy – it is impossible to say for sure.
What seems likely, however, is that this increase has helped to shape the course of & # 39; evolution (and sunset) on this planet, perhaps included the Chicxulub event helped to write off the dinosaurs from the planet's surface.
"Perhaps it is fair to say that was a date with destiny for dinosaurs," says one of the team, the Earth scientist Thomas Gernon from the University & # 39; Southampton in the UK.
"The drop their & # 39; was somewhat inevitable because of the increase of & # 39; big space rocks are asteroids World."
The – findings are reported in & # 39 ;. T science.