7 ways the Earth has changed from ancient to modern times

Our Solar System formed some ~4.6 billion years ago.

Although we now believe we understand how the Sun and our Solar System formed, this early view of our past, protoplanetary stage is an illustration only. While many protoplanets existed in the early stages of our system’s formation long ago, today, only eight planets survive. Most of them possess moons, and there are also small rocky, metallic, and icy bodies distributed across various belts and clouds in the Solar System as well.

Eventually, eight planets emerged, with a giant impact creating Earth’s Moon.

When two large bodies collide, as they very likely did between proto-Earth and a hypothesized smaller but still massive world known as Theia in the early Solar System, they’ll generally merge to form one more massive body as a result, but the debris kicked up from the collision can coalesce into one or more large moons. This was likely the case not only for Earth, but for Mars and Pluto and their lunar systems as well, forming our modern Earth and Moon just a few tens of millions of years after the Sun ignited.

Here are 7 ways the Earth has subsequently changed.

Early on, even small-mass planets like Earth had a large hydrogen and helium envelope. Due to their low gravity, solar wind and radiation swiftly stripped that primitive atmosphere away.

1.) Atmospheric composition. Early on, hydrogen and helium dominated.

Volcanic activity present on Earth, including from the earliest times, released large quantities of solid and gaseous material into our atmosphere, including nitrogen, carbon dioxide, and water, which transformed our young hydrogen/helium atmosphere into a nitrogen/CO2/H2O rich atmosphere, which would, later, further be transformed by biological processes.

Volcanic and biological activities were transformative.

Although the exact ratios of the different atmospheric components of Earth are unknown, there were large amounts of methane present in the atmosphere prior to 2.5 billion years ago and virtually no oxygen. With the arrival of oxygen, the methane was destroyed, and the planet’s greatest ice age began.

Today, our nitrogen/oxygen atmosphere has hints of water, argon, and carbon dioxide.

While modern Earth has had plate tectonic activity for at least the past 2 billion and potentially as much as 4.3 billion years or more, the earliest phases of our planet’s history are expected to have lacked plate tectonics, as it only developed once water arrived and enough differentiation had taken place.

2.) Plate tectonics. Early Earth was lava-rich, possessing poorly-differentiated internal layers.

These tiny zircon crystals, which are only as thick as a human hair, are over 4 billion years old and hold an enormous amount of chemical information about early Earth. The silicon, oxygen, and trace element and isotope contents in these zircons and their parental magmas suggest that plate tectonics existed on Earth more than 4 billion years ago. The graphite deposits found within these zircons exhibit remarkable and interesting carbon isotope ratios, suggestive, but not proof of, a biological origin.

With severe energy gradients, a mobile lithosphere, and liquid water, plate tectonics are undeniable today.

Tidal rhythmites, such as the Touchet formation shown here, can allow us to determine what the rate of Earth’s rotation was in the past. During the emergence of the dinosaurs, our day was closer to 23 hours long, not 24. Back billions of years ago, shortly after the formation of the Moon, a day was closer to a mere 6-to-8 hours, rather than the 24 we possess today.

3.) Length of a day. In ancient times, Earth rotated 360° in just 6-8 hours.

The Moon exerts a tidal force on the Earth, which not only causes our tides, but causes braking of the Earth’s rotation, and a subsequent lengthening of the day. The asymmetrical nature of Earth, compounded by the effects of the Moon’s and Sun’s gravitational pulls, causes the Earth to spin more slowly. To compensate and conserve angular momentum, the Moon must spiral outward. It is for this reason that Earth will no longer have total solar eclipses after another 600 million years, and that the length of each day is getting longer as time progresses.

The amount of time a “day” takes continually lengthens, at ~24 hours presently.

A synestia doesn’t just consist of this puffy ring/torus of debris around a joint planetary core, but also rises to temperatures in excess of 1000 K, causing it to emit substantial amounts of its own infrared radiation, with peaks in different parts of the infrared spectrum dependent on the exact temperature and temperature profile of the system in question. The heat from the early Moon, just 24,000 km away initially, would have played a role in heating the lunar-facing side of the Earth.

4.) Distance to the Moon. Upon initially forming, the Moon was just 24,000 km away.

This unfamiliar view shows the size of the Earth and Moon, plus the distance from the Earth to the Moon, to actual scale. The Earth is about 12,700 km in diameter with the Moon being a little over a quarter of the Earth’s size, but the present Earth-Moon distance averages out to an enormous 384,000 km: just over 30 times the Earth’s diameter.

Tidal braking causes outspiraling, leading to its modern distance of 384,000 km.

Artist’s concept of meteors impacting ancient Earth. Some scientists think such impacts may have delivered water, amino acids, and other molecules useful to emerging life on Earth, as the evidence is strong that the impact and cratering rate across the Solar System was much higher than present for the first 0.6-0.7 billion years of our Solar System’s history.

5.) Frequency of impacts. Ancient impacts were ubiquitous across the Solar System.

This two-faced mosaic from NASA’s Lunar Reconnaissance Orbiter shows the near side (L) and the far side (R) of the Moon with modern technology. By looking at the ratios and sizes of craters found on the Moon with respect to the age of that portion of the Moon, Mars, Mercury, and Earth, we can learn how cratering rates have varied over the Solar System’s history.

Martian and lunar data show an incredible decline in crater-causing impacts.

Early on, shortly after the Earth first formed, life likely arose in the waters of our planet. The evidence we have that all life that’s extant today can be traced back to a universal common ancestor is very strong, but many details concerning the early stages of our planet, for perhaps the first 1-to-1.5 billion years, remain largely obscure. While life arose early on, there is no evidence that Earth came into existence with life already on it, with the origin being uncertain to within 100-700 million years after our planet’s formation.

6.) Presence of life. Initially, Earth was completely uninhabited.

This photograph shows chloroplasts within the plant cells of the organism Plagiomnium affine. The photosynthetic conversion of carbon dioxide, water, and sunlight into sugars, producing oxygen as a waste product, is one biological process that has been truly transformative for Earth’s atmosphere and biosphere.

For 3.8+ billion years, however, life has transformed Earth’s biosphere.

Eventually, the evolution of the Sun will be the death of all life on Earth. Long before we reach the red giant stage, stellar evolution will cause the Sun’s luminosity to increase significantly enough to boil Earth’s oceans, which will surely eradicate humanity, if not all life on Earth. The exact rate of increase of the Sun’s size, as well as the details about its mass loss in stages, are still not perfectly known.

7.) Influence of the Sun. Solar luminosity has increased 40% over the past 4.5 billion years.

After the protostar that would become the Sun contracts and cools sufficiently, nuclear fusion initiates, but the Sun’s luminosity and energy output, once settling down to a level value about 50 million years after its formation, gradually increases over time. 4.5 billion years ago, it was only ~70% the luminosity it is today; in the future, over billion year timescales, the Sun’s energy output will continue to increase.

In another 1-2 billion years, Earth’s oceans will unceremoniously boil away.

Today on Earth, ocean water only boils, typically, when lava or some other superheated material enters it. But in the far future, the Sun’s energy will be enough to do it, and on a global scale. After 1-2 billion years of further solar evolution, Earth will lose all of its liquid water to the gaseous phase, triggering a runaway greenhouse effect, and life is expected to end on our world at that time.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words.