YALLALIE IMPACT STRUCTURE
It may look like a simple bowl-shaped depression in the landscape, but this site is most likely the result of a meteoroid on a collision course with Earth around 83 million years ago. It’s hard to believe but at the time the area of impact was a shallow marine environment.
North east of Badgingarra is a bowl-shaped depression in the landscape, around 12km in diameter with a raised area in the centre 3-4km across. It was most likely caused when a meteorite impacted with Earth, but no human alive today saw this happen, so how do we know this?
Geology can help us gather the evidence. Geology is measured on a timescale of millions of years (Ma) and is categorised into eons, eras, then periods. Yallalie lies in the Perth Basin which was formed when India and Australia separated in the Permo-Cretaceous period, around 66 – 252 Ma.
Geologists can determine that this formation is in rocks from the Mesozoic era, so we know the impact happened somewhere between 66 – 201 Ma. A lot of sediment has accumulated since then so it doesn’t resemble the striking ‘crater’ we have come to expect from meteorite impacts elsewhere.
Geology can help further narrow down the timeframe. By drilling deep into the Earth we can uncover layers called strata which read like a time record. There are two drill holes at the site from petroleum exploration and by examining their strata the impact has been dated to around 83 Ma. Hard to imagine now, but the area of impact was most likely a shallow marine environment back then!
Using digital technology we can further inspect the landscape. Geophysical surveys are carried out using a magnetometer on an aircraft. From this a digital elevation model was created which clearly shows the impact area is different to the surrounding landscape. Further image processing shows radial structures extending 40km from the centre of the depression, a bit like the ripples when you throw a stone into water.
To find out more about meteors and meteorites check out the Desert Fireball Network.
Where to find it
North-East of Badgingarra