The question of whether Mars is geologically “older” than Earth is a matter of perspective, as both planets formed at nearly the same time within the solar system’s initial history. The scientific consensus places the origin of the solar system, including the birth of the inner planets, at approximately 4.57 billion years ago. While both Earth and Mars are the same absolute age, their geological histories diverged dramatically shortly after formation. This difference means Mars preserves an ancient record on its surface, giving it a much older geological appearance compared to Earth’s constantly renewed face.
The Timeline of Planetary Formation
The inner planets were built through a rapid process called accretion, where dust and gas in the early solar nebula collided and stuck together, gradually forming planetesimals and then protoplanets. This building phase occurred very quickly. The overall solar system age is estimated at 4.57 billion years, a figure determined by dating the oldest solids found in meteorites.
Scientists use radioisotopic dating, such as the hafnium-tungsten (Hf-W) chronometer, to pin down the timing of core formation, which serves as a proxy for the bulk accretion time of a planet. Hafnium-182 decays into tungsten-182, making it an excellent tool for dating early solar system events. This evidence suggests that the main growth stage for the terrestrial planets was completed within 10 to 30 million years after the first solids formed. Therefore, in terms of their birth dates, Earth and Mars are essentially planetary twins.
Evidence for Mars’s Rapid Early Formation
Mars appears geologically older because it completed its internal evolution and ceased activity very early in its history. Studies of Martian meteorites indicate that the planet may have fully formed its core and crust within the first 10 million years of the solar system’s existence. This rapid accretion was followed by rapid cooling and geological stagnation.
The surface of Mars provides a direct window into the solar system’s deep past, a time period largely erased on Earth. The southern hemisphere is dominated by heavily cratered highlands, remnants of the early intense bombardment that occurred around 4 billion years ago. These ancient features are preserved because Mars, being smaller than Earth, lost its internal heat quickly. The evidence suggests that the planet’s internal engine, the source of geological activity, shut down.
The lack of global plate tectonics on Mars is the primary reason its surface has remained largely unchanged for billions of years. While early Mars may have briefly had processes like crustal recycling, these systems were not sustained. Martian rocks, including ancient zircons found in meteorites, show that a primordial crust existed on the planet as far back as 4.43 billion years ago. This preserved, ancient crust makes the Red Planet a relic of the solar system’s youth.
Comparing Earth’s Ongoing Evolution
Earth, in contrast, has a geologically young surface due to its sustained internal heat and size. While Earth also formed quickly, its greater mass allowed it to retain internal heat for longer, powering continuous geological processes. The most significant of these is plate tectonics, which constantly recycles the planet’s crust.
Subduction and volcanism continuously create new crust and destroy old crust, effectively erasing the evidence of Earth’s earliest history. This constant resurfacing is why the oldest known terrestrial rocks are only about 4.03 billion years old. Most of the surface we walk on is geologically young.
The presence of a thick atmosphere and liquid water also contributes to Earth’s geological youth by driving powerful erosion. Wind, water, and ice relentlessly break down and sculpt surface features. These forces constantly smooth and alter the landscape, preventing the preservation of ancient cratering records seen on Mars. Ultimately, Mars and Earth share the same age of formation, but the Red Planet’s geological history ended shortly after it began, while Earth’s continues.