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Researcher Mark Harvey says he was looking for evidence of pre-human civilisation when he made a discovery which has cast new light on the extinction of the dinosaurs.
"In my naivety, I used to think it was possible there may have been an advanced civilisation before human beings,"
he said.
Mr Harvey, from Piha, was studying for a masters degree in geology at Indiana University in the United States when he found evidence that the giant asteroid thought to have wiped out dinosaurs 65 million years ago may have done it by vapourising an oil deposit.
The research was published this week in the international scientific journal Geology.
Mr Harvey said he took up the study of geology after gaining a BSc in biology at Auckland University, because he thought that a pre-human civilisation might have left microscopic traces in the sediment record.
He was searching sediment samples for cenospheres - microscopic carbon beads regarded as signs of industrial activity - and found them at the end of the age of dinosaurs.
Accepting the dinosaurs did not have coal smelters or diesel injectors to produce the cenospheres, he investigated how they might have occurred.
His research suggests a huge asteroid hit oil or coal deposits when its impact made the 200km-wide Chicxulub crater, just west of Mexico's Yucatan Peninsula.
It struck with such force that some of the buried carbon liquefied, rocketed skyward, and formed tiny droplets that rained down around the planet among the soot from the impact. Some of the biggest cenospheres, from Canada, were 20 to 30 microns in diameter and golden brown in colour.
Mr Harvey said this may mean the carbon deposit struck by the asteroid was from an "immature" oilfield where hydrocarbons had not yet "cooked" into oil.
The boundary between the Cretaceous and Tertiary epochs 65 million years ago is identified by markers in the geological record - a layer of a mineral called iridium which is rare on Earth's surface but more common in asteroids, and a layer of soot.
Until now many geologists thought the carbon particles resulting from the impact were ash from global forest fires, but Mr Harvey's research has overturned that assumption.
Now a scientist working on geothermal energy for the Sinclair Knight Merz consultancy, Mr Harvey is the lead author for a team of researchers from Britain, the United States and Italy.
They examined carbon in rock samples from eight marine sediments in New Zealand, Italy, Denmark and Spain, and carbon-rich particles from five non-marine locations in the US and Canada.
The NZ sample came from Woodside Creek, in Marlborough.
Mr Harvey's team has estimated the total mass of carbon cenospheres ejected by the asteroid collision was 900 billion tonnes.
The cenospheres became smaller the further the sample site was from the Chicxulub crater - consistent with the heavier particles produced by the asteroid impact falling to earth sooner than lighter particles.
The most distant samples, in New Zealand, were only 3 or 4 microns wide - a micron is just one thousandth of a millimetre and an average human hair measures 60 microns in diameter.
- NZPA
