Earth’s First Geologists

Earth’s Billion-Year Mystery

When the first geologists explored the Grand Canyon, they discovered a billion-year mystery that we still haven’t solved. John Wesley Powell, on his 1868 expedition, called the mile-high canyon walls the “The Library of the Gods” – where he saw 2 billion years of Earth’s history piled in rock layers one atop the other … Except, he realized, there were hundreds of millions of years of rock layers missing! Later geologists found this great "unconformity" -- a break in the geologic rock record -- everywhere. All around the world, the same billion years of rock was simply … gone. What happened? One hypothesis holds that, long ago, when Earth was repeatedly covered in ice for many millions of years, glaciers slid and moved over continents and abraded them down by a mile or more. Another hypothesis relates to heat. For about half a billion years, all of Earth’s land surface was concentrated in one supercontinent called Rodinia. With fewer outlets for Earth’s mantle heat, Rodinia would have expanded and uplifted by a few miles. Erosion before, during and especially following that uplift could have stripped away a mile of rock. More likely, it was a combination of events that washed billions of tons of eroded minerals into the ocean – to enrich and support the Cambrian Explosion of Life that happened just after. A billion-year mystery that eventually led to ... us.

The Humongous Fungus Among-Us

Beware, there’s a humongous fungus among us! And if you visit the Malheur National Forest in Oregon, you can walk among it—though you might not know it… Unless you notice that many of the spruce trees are sprouting mushrooms. And if you DNA tested them, you’d see that each one is genetically identical—because they’re all part of a single gigantic organism, a clonal colony of Armillaria ostoyae, the honey mushroom. How big is it? Well, the blue whale is the heaviest animal, at 300,000 pounds. We told you on another EarthDate about the heaviest organism, an aspen grove in Utah that weighs 13 million pounds! But in terms of area, the humongous fungus has them beat. This one organism covers more than four square miles—and mostly underground! The fungus is a massive network of black rootlike filaments called rhizomorphs. It spreads in the soil from tree to tree, invading root systems and eventually the trunk, where it digests the live wood. Once it sprouts into mushrooms at the tree base, the damage is already done. When the tree dies, the fungus will digest the dead wood, too. Scientists estimate this one fungus is more than 8,000 years old and still spreading. If you want to help the forest fight back, you can go and pick some honey mushrooms. When cooked correctly, the humongous fungus … is delicious!

Earth’s First Geologists

Four to six thousand years ago, humans invented metallurgy. Until that time—for 99 percent of hominid history—we were living in the Stone Age. The earliest evidence of prehumans using stone tools comes from 3.4 million years ago, with tool marks found on fossil animal bones in East Africa. The earliest, very primitive stone tools come from 3.3 million years ago, probably used by Australopithecus or Homo habilis. Around 1.7 million years ago, our ancestors developed more-advanced tools, chipping flakes off the sides of stones to make a sharp cutting edge. Around 70,000 years ago, and possibly much earlier, toolmakers began to research the properties of rock. In a cave shelter in South Africa, scientists found evidence that early Homo sapiens were testing some types of rock for ease of working and others for durability—could the edge stand up to repeated use. These toolmakers initially preferred quartzite, a hard metamorphic rock that fractures predictably, to make sharp, finely crafted spearpoints. Five thousand years later, they had shifted to making small arrowheads from more fragile silcrete, which shaped easily and may have been designed to break apart in prey, disabling them. These early humans carefully selected their raw stones with an understanding of what tools they could become. You could call them our first geologists!

Mother of Landsat

Have you ever seen those beautiful satellite images of Earth and wondered what camera could take them? The answer is no camera could. They’re produced by a multispectral scanner developed in the 1950s at Hughes Aircraft by a team led by the young MIT scientist Virginia Norwood—known today as the “Mother of Landsat.” Landsat, Earth-imaging satellites, were first launched in 1972 by NASA with the goal to survey the Earth’s surface in real time. The orbital path was set from pole to pole, and they could circle Earth several times a day, taking a full image of Earth every 18 days. But how would they take that image? RCA developed a television-like system using camera lenses recording to early black and white video. But Norwood’s team had a different idea. They captured light reflected from Earth, from within and outside of the visible spectrum, and separated it into multiple electromagnetic bands. They analyzed Earth’s surface using the different properties of each band. Finally, the bands were composited into an image. Early satellites carried RCA’s and Norwood’s systems, but hers quickly won out and became the standard for satellite imaging, now covering Earth every eight days. Norwood continued to advance the field for her entire career, until she retired in 1989—a pioneer whose work is used daily in agriculture, forestry, fisheries, geology, cartography, military applications and many other fields.

Living in Lava Tubes

For thousands of years, humans have found shelter in lava tubes. In the future, they may do the same—on the Moon! A lava tube is a cave. It forms when lava flowing in a channel forms a crust on the upper surface that’s exposed to cooler air. The crust insulates the lava below, which gets superheated and melts a deeper tube-shaped channel as lava continues to flow through it. When the lava runs out, it leaves a tunnel. In places with lots of volcanic activity, there are networks of lava tubes, some of them miles long. Openings to the surface, called skylights, let in rain and sun and have made lava tubes habitable cave environments for wandering humans for millennia. Scientists have evidence that the Moon and Mars also have lava tubes, which could be perfect locations for potential future human colonies, sheltered from cosmic rays and meteorites. In those lower gravity settings, lava tubes should be much wider and taller than on Earth. So large in fact, that they could hold an entire colony. Lava tube networks could also provide routes for roads and perhaps lead to reservoirs of water ice. For these reasons, future missions to the Moon and Mars will use ground-penetrating radar to search for lava tubes. And if humans one day colonize space, they may start in shelters like those that protected their ancient ancestors on Earth.