How Did Earth Get Its Atmosphere? The Story of Our Planet’s First Air Earth’s atmosphere seems like a permanent part of the planet, but it was not there in its present form when Earth formed about 4.6 billion years ago. The young Earth was extremely hot, and the gases surrounding it were very different from […]
How Did Earth Get Its Atmosphere? The Story of Our Planet’s First Air Read Post »
Why Does the Moon Have So Many Craters? The Moon’s surface is covered with thousands of craters. Most were created when asteroids, meteoroids, and comets struck the lunar surface over billions of years. But impacts alone do not explain why the craters are still so easy to see. The main reason is that the Moon
Why Does the Moon Have So Many Craters? Read Post »
Earth’s Moon is unusually large compared with its planet. For decades, scientists have tried to understand how this close companion formed about 4.5 billion years ago. Several ideas have been proposed, but the giant impact hypothesis is now the leading explanation. It suggests that the young Earth experienced a massive collision, and material thrown into
How Did the Moon Form? The Giant Impact Theory Explained Read Post »
Earth is covered with water today, but it did not begin with oceans. The young planet formed about 4.5 billion years ago in a hot, violent Solar System, and liquid water had to accumulate as Earth cooled. So, how did water come to Earth? Scientists think it was probably a combination of sources and processes.
How Did Water Come to Earth? The Story of Earth’s Oceans Read Post »
Earth formed about 4.5 billion years ago from material left over from the formation of the young Solar System. Dust and rock around the young Sun gradually collided, stuck together, and grew into larger bodies. Over millions of years, these bodies merged through accretion—the gradual buildup of a planet by collecting more material. Eventually, one
How Did Earth Form? A Step-by-Step Look at Earth’s Formation Read Post »
The Sun formed about 4.6 billion years ago from a dense cloud of gas and dust in the Milky Way. Gravity pulled part of this cloud inward, causing it to collapse and form a growing object at its center. As the material collapsed, it began rotating faster and flattened into a disk. Most of the
How Was the Sun Formed? The Story of Our Star’s Birth Read Post »
The Solar System formed about 4.6 billion years ago from a dense cloud of gas and dust. Gravity pulled the cloud together, forming a spinning disk around the young Sun. Within that disk, dust and rock gradually joined to build planets, moons, asteroids and comets. Scientists have reconstructed this process from meteorites, observations of young
How Did the Solar System Form Step by Step? Read Post »
We see the Milky Way as a broad band of stars across the night sky, but the galaxy itself was not created in one event. The Milky Way formed gradually as gravity brought matter together, gas collected, stars formed, and smaller galactic systems merged over billions of years. Its earliest building blocks appeared more than
How Was the Milky Way Formed? From Early Stars to the Galaxy We See Today Read Post »
The universe is expanding, but scientists discovered that its expansion is not slowing down. It is accelerating. So how do scientists know dark energy exists if they cannot see it? The answer comes from measuring how the universe has expanded over time. Distant supernovae, observations of the cosmic microwave background, and measurements of large-scale cosmic
How Do Scientists Know Dark Energy Exists? Read Post »