Olsen and his collaborators, however, believe that Lucas’ footprint interpretations and age estimates are wrong. He prefers an alternative Chinle timeline constructed by William Parker, a National Park Service paleontologist. Parker claims to correct a major error in Lucas’ timeline — the accidental omission of nearly 200 feet of strata. When Parker adds the omitted strata back into his timeline, the overall chronology changes: The upper layers of the Chinle formation are about 5 million years younger — no more than 207 million years old.
Parker’s estimate, if correct, means those Chinle layers lacking prosauropods are young enough to align with strata from high-latitude areas of Pangaea where the fossil record shows prosauropods had become plentiful. This heightens the contrast between dinosaur populations at the high and low latitudes. And it’s just what Irmis and Olsen would expect, since they believe prosauropods and other large dinosaurs thrived for 30 million years at high latitudes before managing to establish in the tropics after a mass extinction 201 million years ago.
Just before dusk, I walk with Olsen away from the roar of the drill site to the edge of the mesa. It overlooks a layer of petrified tree trunks, dusted white with ancient volcanic ash. Volcanoes often sprinkled ash here during the Triassic, and scientists can date that ash by counting uranium and lead atoms caged inside tiny, near-microscopic zircon crystals. The white layer below us has been dated at 210 million years, one of only a dozen or so hard dates obtained for the entire Petrified Forest. Olsen’s collaborators will date thousands more zircons up and down the 1,600-foot core being drilled behind us.
“It would be nice if there’s a smooth progression of ages down the hole,” says Olsen. It would help them line up the Chinle and Newark cores and rebuff Lucas’ criticisms. But ages in the core might also be scrambled, with older zircons layered above younger ones.
It is true in geology that rock equals time, but most rock is made of materials recycled from elsewhere on Earth. The badlands stretching out below Olsen and me originated from ancient mountain ranges in what are now Texas, California and Canada. Those mountains eroded, sending more than 1,000 cubic miles of sediment and older zircons tumbling down rivers and settling in the northern Arizona Chinle region over 200 million years ago, building the rocks we see here. Olsen’s collaborators hope to sort out the zircon age problem by selectively dating ones with sharp rather than battered edges — those that came from the sky rather than a riverbed.
Planets in Motion
If the Chinle cores yield a coherent sequence of dates, and if they agree with the Newark timeline, they could also shed light on the past and future movements of planets in our solar system.
When Olsen studied his Newark cores in the mid-1990s, he noticed something odd. The Milankovitch cycles recorded in the rocks lined up well with those known in today’s world, with one exception: A much longer cycle, marking a subtle gravitational tug-of-war between Mars and Earth, was off. Instead of 2.4 million years (as it is today), Olsen’s cores showed the cycle lasted 1.75 million years. It was a hint that the movement of planets in our solar system hasn’t always been what it is today.
When Olsen presented these results at a meeting in 1999, the man who followed him at the podium was visibly excited by what he had just seen. “That was exactly what I was proposing to do,” he told the audience.
The man was Jacques Laskar, an astronomer at the Institute for Celestial Mechanics in Paris. He had spent a decade working on a 200-year-old problem: whether the planets’ orbits are stable, or if they drift unpredictably over time.
Laskar’s theoretical calculations for Mercury, Venus, Earth and Mars suggested the latter — that orbital deviations of just 50 feet will propagate to 240 million miles over 100 million years due to tiny shifts caused by gravitational tides in the planets’ interiors and other factors. Now, Olsen had unexpectedly provided evidence that it could be true. The implications were breathtaking.
Laskar’s analysis suggests that 1 billion to 3 billion years from now, Mercury could be tossed from its orbit, whereupon it might crash into the sun, slam into Venus or possibly even sling Mars onto a collision course with Earth, mashing our planet into a glob of molten rock.
The chances appear remote; Laskar’s simulations show Mercury tossed from its orbit only 1 percent of the time. But other outcomes could still prove disastrous. Venus could go awry and crash into Mercury, unleashing millions of large fragments, some potentially colliding with Earth. And a near miss between Earth and Mars could cause much of the Martian crust to be ripped off by Earth’s gravity, pulling thousands of meteors onto our planet.
This scary talk is speculative, but if the Chinle results match what Olsen and his team saw in Newark, those data on orbital variations could help Laskar better quantify the risk.
All of this remains a work in progress. The Chinle cores have already undergone CT scans to map their internal structure, and in February, Olsen and his colleagues began examining them in detail by eye — the first step in detecting evidence of Milankovitch cycles. Lucas, for his part, is surveying amphibian, crocodilian and dinosaur fossils found at over 800 sites across the western U.S. to refine his own timeline of when species appeared and vanished during the late Triassic.
Whichever timeline wins out — Olsen’s or Lucas’ — one thing is clear: Finding a way to measure deep time will shed light on all manner of questions from evolution to astronomy to eschatology, many of them not yet asked.
[This article originally appeared in print as "Sands of Time."]