Science finds many tricks for traveling to the past

Talking about her cover story on what iron-loving elements are telling geologists about the Earth’s deep past, Alexandra Witze likens these rare metals to time travelers. They can tell you, she says, what was happening more than 4.5 billion years ago, during the first 50 million years of our planet’s existence. By then the Earth’s molten interior had begun to settle into its current layer cake form: a dense, solid inner core surrounded by an outer liquid core — both rich in iron and metals such as gold, platinum, ruthenium and others that tend to form alloys with iron. The scarcity of these metals in the outer layers of the planet — the mantle and crust — make them precious to us.
Their high melting points and other properties help them resist change, allowing geoscientists to use them as fingerprints that mark events in the distant past. With new, more precise analytic techniques, scientists can now measure the amounts of these iron-loving metals relative to other elements to deduce what happened to them over eons of time. These traces are found in some very old rocks, Witze reports (SN: 8/6/16, p. 22), such as 3.8-billion-year-old deposits in Greenland. But the metals also show up as ancient time capsules in younger rock. Studying these traces reveals the imperfect mixing of the mantle and can provide insight into outstanding questions, such as why amounts of these metals differ in the mantles of the moon and Earth.
Science is surprisingly adept at this type of virtual time travel. Researchers have repeatedly come up with ways to discover facts about the distant past. In this issue of Science News alone, several new findings illustrate the ability of science to figure out things that would seem impossibly difficult to know. A black hole in a distant galaxy formed over 13 billion years ago, for example, so long ago that it’s hard to even imagine reconstructing the events that led to its birth. But scientists have now pieced together clues, Christopher Crockett reports (SN: 8/6/16, p. 7), that it formed by the direct collapse of a massive gas cloud, rather than from the death of a massive star (the more common origin of black holes).

Reconstructing the evolution of the tail has been stymied by a lack of fossils from creatures that led the transition from water to land. But that hasn’t stopped scientists eager to explore the biomechanics of fishlike animals attempting to hop out of the water and up a slope. Studies of big-tailed fish called mudskippers highlight the utility of a tail in balancing flipper-hops up a sandy incline, Susan Milius reports (SN: 8/6/16, p. 13). To describe the math, scientists built a robot and made it scale an unsteady hill of shifty poppy seeds or plastic bits. Their conclusion: The tail could have been a big assist to flippered creatures emerging on sandy shores several hundred million years ago.

The story on Homo naledi by Bruce Bower (SN: 8/6/16, p. 12) shows why sometimes scientists might just prefer to actually time travel. Efforts to date the bones of this hominid species have proved frustrating; the latest estimate, 912,000 years old, was deduced from evolutionary trees. Knowing how old H. naledi actually is might reveal the diversity of relatively recent hominid species, and perhaps help piece together the story of how Homo sapiens became the sole survivors. That’s some time travel I’d be interested in booking.