Yarrabubba (published 3/02/2020)
Figure 1 Meteorite Impact (credit chaostrophic.com)
Two billion, six hundred million years ago, at the beginning of a geologic age named the Siderian Era, the Earth had already been in existence for two billion years. Prior to the Siderian, so much had happened: the Moon formed from its collision with Earth; evidence of the earliest life only a few hundred million years after Earth formed; the planet was pummeled by meteorites during the “Late Heavy Bombardment”; domination of prokaryote single celled bacteria; first evidence for photosynthesis; accumulation of huge iron deposits; first supercontinent appears; the commencement of plate tectonics; and the formation of huge fossil stromatolite beds. Early in the Siderian Era, even though energy from the Sun was 20 percent weaker than today, the Earth was very hot due to an excess of the greenhouse gases methane and carbon dioxide in the atmosphere; there was no ice on Earth, even at the poles.
But the climate began to radically change; here’s how. First the plate tectonic engine began to break up the supercontinent, creating vast shallow seas favorable to the prolific spread of photosynthetic single-celled cyanobacteria. This changed climate patterns resulting in excessive rainfall, which purged great quantities of carbon dioxide from the atmosphere, depositing it into the sea. Cyanobacteria consume carbon dioxide and expel oxygen as a waste product of photosynthesis. Copious amounts of oxygen were in turn pumped into the atmosphere, which then reacted with the methane, the most potent greenhouse gas, breaking it down into water and carbon dioxide. This became known as the Great Oxygen Event (GOE), the first stage of adding oxygen to Earth’s atmosphere. Oxygen is toxic to cyanobacteria; because the ocean became saturated with oxygen, the colonies of cyanobacteria disappeared, leaving the oceans nearly lifeless.
With a dim Sun producing 20 percent less energy, combined with the removal of nearly all of the greenhouse gasses that heated up the planet, Earth rapidly cooled and plunged into its first major ice age. The Huronian period of glaciation would last for nearly three hundred million years. Some cycles within the Huronian were so severe that they became characterized as “Snowball Earths”, covering over 70 percent of the surface with ice. Because ice reflects sunlight, and there were sparse greenhouse gasses to warm the atmosphere, the average surface temperature often hovered around 70 degrees Fahrenheit below zero. Unless the Creator were to intervene, all life on Earth – those gazillions of tiny cells and bacteria - appeared to be doomed!
When it comes to regulating the Earth, sometimes I think of God as having a toolbox. Not anything like my toolbox with hammers and screwdrivers, rather one containing tools like meteorites, bacteria, changing the orbits of planets (e.g. The Grand Tack), and plate tectonics. He does things on a grand scale. One such tool is a discovery made by researchers in 2020 – Yarrabubba.
Yarrabubba is a meteor crater located in a remote desert in southwest Australia about 100 miles north of Perth (see Figure 2).
Figure 2 Location of Yarrabubba Crater (credit sciencenews.org)
It is not the discovery of this crater that is so significant, Yarrabubba has been known about for decades. What is newsworthy is its age; it has recently been accurately dated at 2.229 billion years ago, making it the oldest meteor crater ever discovered on the planet. Next youngest impact craters are Vredefort Dome in South Africa (2.023 billion years old) and Sudbury in Canada (1.85 billion years old). Why is that newsworthy? Because this meteorite struck Earth toward the end of the 300 million-year Huronian Ice Age. Many scientists believe, were it not for this meteorite and the radical changes it made to our climate, life on Earth might never have survived such a long and intense an ice age. God might have had to start creating life all over again.
Figure 3 Yarrabubba Crater Wall (credit ExplorOz)
This begs two questions: 1) how do scientists know how old it is; 2) how could a meteor drastically change the climate? Let’s deal with the first question.
Figure 4 Zircon Crystal from Yarrabubba Rocks (credit dailymail.co.uk)
Zircons (zirconium silicate, ZrSiO4) are the oldest geological time capsules used for radiometric dating. When a zircon crystal first forms, it traps uranium atoms (U-238) and repels lead atoms (Pb-206). Uranium 238 is unstable, and after many phase changes, will convert over to the stable, non-radioactive Lead 206. In 4.5 billion years, exactly half of the U-238 will have converted to Pb-206; that is called its half-life. This makes zircons an accurate clock to date a substance or event. The conversion of U-238 to PB-206 goes through a series of temporary phases called a decay chain; here is a partial list of its phase changes: uranium 238 > thorium 234 (takes 4.5 billion years) > uranium 234 (for 24.5 days) > thorium 230 (for 8,300 years) > radium 226 (for 1,590 years) > radon 222 (for 3.825 days) > polonium 218 (for 3.08 minutes) > bismuth 210 (for 22 years) > polonium 210 (for 140 days) > lead 206. The Yarrabubba impact site is loaded with zircon crystals. The meteorite struck with such force that any lead would have vaporized in the extreme heat and not been trapped by the zircon crystals; thus, the zircon specimens analyzed for age-determination – shock-reset zircons - would have started out with only U – 238 and zero Pb-206 – totally uncontaminated!
Just as a side-note, young earth creationists, to discredit this incredible tool used by geologists to date the earth, have often been critical of radiometric dating methods. But the truth is, the science of radiometric dating is thoroughly proven, reliable, and precise. Also note, a Ga is the designation for billions of years.
Second question: how might Yarrabubba meteorite have ended an ice age? Evidence for the Huronian Ice Age can be found all over the world, but especially in Australia, Canada, and South Africa. Ice covered large portions of our planet for nearly 300 million years, with at least four major peaks of activity; they are: Ramsey (2.45 Ga); Bruce (2.38 Ga); Gowganda (2.33 Ga); and Rietfontein (2.225 Ga). Dating for Yarrabubba (2.229 Ga) coincides almost exactly, within the margin for error, with the Rietfontein (2.225 Ga) date – a match. Based on geologic evidence, scientists have reconstructed the target zone for the meteor. They believe it was a two-mile-thick ice sheet covering a shallow ocean, beneath which was a blanket of carbonate sediments. Yarrabubba, a meteorite of three miles diameter, struck with such force that it created a 43-mile diameter crater. The intense heat generated by the impact shot huge quantities of water vapor and carbon dioxide, potent greenhouse gasses, high into Earth’s atmosphere, where they would remain for decades. Runaway global warming melted all the ice sheets, ending the ice age, and opening the door to a rise in quantity and types of new life forms.
Figure 5 Shungite rock (credit WordPress.com)
Immediately following this meteorite strike, Earth entered into one of the most baffling and unstable periods in its history, the Lomagundi – Jatuli Excursion. From 2.2 to 2.0 Ga, carbon isotopes (C-13) were wildly out of balance, and the atmosphere ballooned to nearly 35 percent oxygen (compare to the 21 percent of today). Oxygen levels skyrocketed because at this time, there were no land creatures to breathe (consume) it. During the same period, shallow water cyanobacteria excreted huge amounts of waste carbon compounds onto the sea floor with very few organisms around to eat it as food. As a result, massive amounts of carbon “sludge” accumulated; over time some of this carbon was compressed into a unique rock called “shungite”, forming strata hundreds of feet thick.
Note: Definition: shungite is a soft, black, lustrous, non-crystalline mineraloid of biological origin consisting of 98 weight percent of carbon; most deposits are found in Russia. For centuries, shungite has been used to purify water, protect against electromagnetic radiation, reduce stress, promote physical healing, and burn as fuel.
