def convert_types(record):
    """Converts string values to their appropriate type."""
    # Only the year part of the datetime string is significant
    record['year'] = int(record['year'][:4])

    record['mass'] = float(record['mass']) if 'mass' in record else None

    geolocation = record['geolocation']
    geolocation['latitude'] = float(geolocation['latitude'])
    geolocation['longitude'] = float(geolocation['longitude'])

    return record