Next Generation Science Standards


NGSS.HS-ESS1-6


Performance Expectation

Apply scientific reasoning and evidence from ancient Earth materials, meteorites, and other planetary surfaces to construct an account of Earth’s formation and early history.

Think of this performance expectation as one that pinpoints whether your students can prove that Col. Mustard murdered his victim in the library with a candlestick.

Well, maybe that's not exactly what it does, but it basically asks whether your fledgling flatfoots and D.A.'s can piece together details of Earth's birth and difficult early childhood from physical evidence that's pretty spotty. A "cold case," as it were.

And once they've pieced those details together, can they convince others? It's a tall order. After all, what self-respecting prosecutor would try a case that hinged on a fistful of strange crystals, moon rocks, some stuff that fell from outer space, and what somebody saw through a telescope?

A logical one, that's who. That's why this expectation is a toughie but goodie: it requires students to rely on scientific reasoning to make sense of far-flung (no kidding!) and bizarre-o clues.

Have your students hone their investigative chops with these activity ideas:

Disciplinary Core Ideas

ESS1.C – The History of Planet Earth: Although active geologic processes, such as plate tectonics and erosion, have destroyed or altered most of the very early rock record on Earth, other objects in the solar system, such as lunar rocks, asteroids, and meteorites, have changed little over billions of years. Studying these objects can provide information about Earth's formation and early history.

To put the pieces together when it comes to figuring out how old Earth is and how it formed, students will first need to understand that rocks are constantly getting recycled here on Earth. Processes like plate tectonics and erosion turn old rocks into new rocks, meaning even when we use techniques like radiometric dating, we're only figuring out how old the new rocks are, not the old ones.

That left scientists with quite a conundrum, and so they started looking at stuff floating around in our solar system for answers. Students should know that meteorites, in particular, but also moon rocks and other debris orbiting the sun, have remained largely unchanged since they were formed, all dating back to 4.6 billion years ago.

Knowing that, students will see how all the clues add up to the Earth and all the other bodies orbiting the sun coming together 4.6 billion years ago, sort of like how a jello salad congeals all at once and traps all the fruity bits into place.

PS1.C – Nuclear Processes: Spontaneous radioactive decays follow a characteristic exponential decay law. Nuclear lifetimes allow radiometric dating to be used to determine the ages of rocks and other materials. (Secondary to HS-ESS1-6)

Students should know the method use to date rocks, and that's radiometric dating. You don't need to get too heavily into the physics of nuclear decay (save that for HS-PS1-8), but students should know that certain large atoms undergo radioactive decay. Similarly, certain isotopes of otherwise stable atoms also undergo radioactive decay. In all cases, this decay happens at a steady, predictable rate.

For example, we know how long it takes for half of rubidium atoms in a meteorite to morph into strontium atoms. And we know how long it takes for half of one of those halves to morph. And so on. That means the ratio of rubidium to strontium atoms found in a meteorite can tell us how old it is.

Science and Engineering Practices

Constructing Explanations and Designing Solutions: Apply scientific reasoning to link evidence to the claims to assess the extent to which the reasoning and data support the explanation or conclusion.

The primary goal for this performance expectation is to let students learn firsthand how scientists were able to determine the age of Earth. By approaching the problem and walking through all the scientific evidence scientists drew upon, they should be able to use reason to put all the pieces together.

Let students do a lot of the initial problem solving in groups or teams, and they'll be able to help each other make sense of radiometric dating, the birth of the solar system, and why Earth is a lousy place to look for clues in rocks.

From there, they can synthesize all their newfound knowledge by doing presentations, peer teaching, posters, or even more creative stuff like comic books or stories that narrate how we determined the age of Earth.

Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena: A scientific theory is a substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment and the science community validates each theory before it is accepted. If new evidence is discovered that the theory does not accommodate, the theory is generally modified in light of this new evidence.

Students should know that theories are mainstays of science, and they always function as explanations for what we observe in the natural world. The second important aspect of a scientific theory is that it not only explains something, but is supported by gobs of evidence.

In the case of dating Earth, the oldest rocks we've been able to find are around 4.4 billion years ago, but we know Earth tends to recycle rocks. So, we instead look to the rest of our solar system. When we date things like meteorites or moon rocks, we find that they're consistently 4.6 billion years old. That's no coincidence, and that provides the empirical evidence used to support the theory of when and how Earth was formed.

Science Models, Laws, Mechanisms, and Theories Explain Natural Phenomena: Models, mechanisms, and explanations collectively serve as tools in the development of a scientific theory.

Students should realize pretty readily what the big hurdle is in trying to figure out when and how Earth was formed: it happened a really, reaaaaally long time ago, and there wasn't anyone around with a GoPro camera to record it. That being the case, scientists have to rely on models to make sense of the evidence they do have.

Make sure that students understand when they're looking at radiometric data or drawing out how the solar system formed that they are using models to make sense of evidence. Models, simply put, are just representations we use as scientists to illustrate whatever we can't see with our own two eyes.

Crosscutting Concepts

Stability and Change: Much of science deals with constructing explanations of how things change and how they remain stable.

Your students should understand that science is all about understanding and explaining the world around us. Since the world around us a hodge-podge of systems in flux and others staying the same, that's what we have to work with.

Earth and the rest of the solar system is a prime example of this. Here on Earth, rocks are constantly recycled thanks to erosion and plate tectonics. Other stuff circling around in our solar system, on the other hand, has hardly changed since the solar system was formed. Knowing that, we can look to those unchanged meteorites and space rocks for evidence about when and how Earth was formed.