LIFE × EARTH

Life's Ingredients Fell from the Sky

~4.3 billion years ago

Hadean

Meteorites rich in carbon carry amino acids and, in far smaller traces, the sugar ribose and the bases that spell out the genetic alphabet: parts for proteins, RNA and DNA. Every one of these molecules was put together in space, with nothing alive involved. The same kind of material rained onto the young Earth, brought in by asteroids, comets and the dust that drifts between the planets.

Why it matters

The chemistry life runs on did not have to be invented from scratch on each planet: part of it arrives already made. Whatever assembled the first living things had a stock of parts to draw on, and nothing about that delivery is particular to Earth.

Dating & uncertainty

These molecules are measured in meteorites that fell recently, and their birth beyond Earth is signed twice over: the carbon isotopes of the sugars have the wrong mix for anything grown here, and the amino acids come in equal amounts of left- and right-handed forms, a balance living chemistry never keeps. The quantities are minute and very unequal, parts per billion for the rarer amino acids and a thousand times lower still for the nucleobases. What stays a deduction is how much of it reached the ground intact through the early atmosphere.

Sources

1. Meierhenrich et al. (2004), PNAS · Identification of diamino acids in the Murchison meteorite
2. Koga & Naraoka (2017), Scientific Reports · A new family of extraterrestrial amino acids in the Murchison meteorite
3. Furukawa et al. (2019), PNAS · Extraterrestrial ribose and other sugars in primitive meteorites
4. Oba et al. (2022), Nature Communications · Identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites

Earth history as one day

01:16:0722 h 44 min before midnight

if Earth’s 4.54 billion years were compressed into a single day