But perhaps the clearest example of life shaping Earth’s land, sea, and air is much more recent — and, in fact, currently playing out. “I’d say humans are among the dominant forces of change on the planet,” Mustard says. Much of his career has been dedicated to observing how Earth’s surface changes in response to both natural and human forces. And there are plenty of human forces at work.
We remove or replace vegetation. We exhaust or reroute water supplies. We populate and reshape coastlines. And we produce or release massive amounts of atmosphere-altering gases. Many of these effects can be observed with relatively coarse data and commercially available software, Chojnacki says.
Fortunately, earth science is different from other planetary science in one final, fundamentally important way: Earth science is actionable science. By monitoring the changes our host planet undergoes, we can make choices and take actions that reduce or alter our effect on the landscape.
“What we learn from spaceborne measurements can have very practical applications to human society — e.g., wildfire management, forest management, disaster management, improving agriculture, managing air pollution, managing biodiversity, etc.,” Margolis says. And Chojnacki notes that the same remote-sensing techniques researchers use to determine how humans are affecting the planet can also show us how well mitigation efforts are progressing.
Earth and Venus: Separated at birth
Venus and Earth are stunningly similar; in fact, Venus is often called Earth’s sister planet. At first glance, it’s easy to see why: Earth is a mere 1.1 times as wide and 1.2 times as massive as Venus, and they’re made up of largely the same material in equal amounts.
Yet, the two look vastly different. It’s an experiment in how small initial differences can snowball into huge effects further down the line, leading one planet to become the lush, water-filled paradise we enjoy today, while the other becomes a broiling, toxic wasteland. But research suggests both may have started out with roughly the same amount of water. So, what happened? That’s the million-dollar question.
We do know that Venus rotates retrograde, or backward, compared to its orbital motion around the Sun — the only planet to do so. Although its core is still hot, like Earth’s, Venus has no plate tectonics. Its oppressively thick atmosphere is about 96 percent carbon dioxide, 4 percent nitrogen, and less than 0.1 percent other gases. Earth has a comparatively light atmosphere consisting of 78 percent nitrogen, 21 percent oxygen, and 1 percent other gases.
Despite these differences, Earth’s strange sister still has much to offer. Venus doesn’t look much like modern-day Earth, but scientists think the two were much more similar shortly after formation, potentially making Venus a good analogue for a younger Earth.
“Venus is the only planet that can teach us both about early Earth and the birth of both plate tectonics and continents — two processes that have profoundly shaped life on Earth,” says Suzanne Smrekar, principal investigator of the Venus Emissivity, Radio Science, InSAR, Topography & Spectroscopy (VERITAS) mission, which is currently under consideration for NASA funding. Smrekar also worked on the Magellan spacecraft that orbited Venus in the early 1990s.
“On Earth, plate tectonics is the fundamental process that links the interior heat engine to surface geology and releases (and recycles) volatiles from the interior to create the atmosphere,” Smrekar says. “Yet this process began billions of years ago, leaving only vague clues about how it started. There are many models but little data. By going to Venus … we have a chance to see processes that shaped the birth of our home planet in action!” — A.K.