Presumably, after the dinosaur killing asteroid, there was a 10 year winter, and it was this that preserved, like a fridge, the dead plant/animal material. This allowed the surviving small mammals to have a source of food until photosynthesis could restart the food chain?
The asteroid impact at the end of the Cretaceous period, about 66 million years ago, triggered a global "impact winter" due to massive amounts of dust, soot, and sulfur aerosols ejected into the atmosphere, blocking sunlight and causing widespread darkness and cooling. Recent modeling based on fine silicate dust from the Chicxulub crater suggests this atmospheric blockage persisted for around 15 years, with global temperatures dropping by up to 15°C (59°F). Photosynthesis was severely disrupted or halted entirely for nearly 2 years in many regions, leading to a collapse of primary production and the base of the food chain. Earlier estimates varied, with some suggesting the most intense cooling and darkness lasted months to decades, but the 10-year figure you mentioned aligns broadly with the decade-scale blackout described in several analyses. Your idea about the cold preserving dead plant and animal material "like a fridge" is a reasonable inference, though not always explicitly framed that way in the literature. The drastic cooling would have slowed microbial decomposition, allowing organic detritus (dead vegetation, carcasses, and other biomass) to persist longer as a food source in the absence of fresh plant growth. This detritus-based food web likely played a key role in sustaining survivors during the initial years of recovery, before ecosystems could rebound. Small mammals (our distant ancestors) were among the groups that endured, but their survival rate was low—only about 7% of mammalian species made it through the Cretaceous-Paleogene (K-Pg) boundary. Key factors in their success included: Small body size: Most survivors were rat- or mouse-sized, requiring less food and energy. This allowed them to burrow underground or shelter in protected microhabitats, shielding them from immediate post-impact effects like infrared radiation pulses, wildfires, and tsunamis. Generalist diets: Unlike specialized herbivores or carnivores that perished, surviving mammals were often omnivorous, able to scavenge detritus, seeds, fungi, insects, and decaying matter. This flexibility was crucial when live plants and prey were scarce. Habitat preferences: Ground-dwelling or semi-arboreal species fared better than fully tree-dependent ones, as the impact devastated forests globally through fires, acid rain, and blocked sunlight. Once the dust settled and sunlight returned, photosynthesis gradually restarted, enabling plant recovery and the rebuilding of food chains. In the ensuing Paleogene period, mammals rapidly diversified, increasing in size, species richness, and ecological roles—eventually leading to the dominance we see today. This opportunistic explosion filled niches left vacant by extinct dinosaurs and other groups.